An analytical model for highly seperated flow on airfoils at low speeds

NASA Technical Reports Server (NTRS)

Zunnalt, G. W.; Naik, S. N.

1977-01-01

A computer program was developed to solve the low speed flow around airfoils with highly separated flow. A new flow model included all of the major physical features in the separated region. Flow visualization tests also were made which gave substantiation to the validity of the model. The computation involves the matching of the potential flow, boundary layer and flows in the separated regions. Head's entrainment theory was used for boundary layer calculations and Korst's jet mixing analysis was used in the separated regions. A free stagnation point aft of the airfoil and a standing vortex in the separated region were modelled and computed.

Simultaneous visualization of transonic buffet on a rocket faring model using unsteady PSP measurement and Schlieren method

NASA Astrophysics Data System (ADS)

Nakakita, K.

2017-02-01

Simultaneous visualization technique of the combination of the unsteady Pressure-Sensitive Paint and the Schlieren measurement was introduced. It was applied to a wind tunnel test of a rocket faring model at the JAXA 2mx2m transonic wind tunnel. Quantitative unsteady pressure field was acquired by the unsteady PSP measurement, which consisted of a high-speed camera, high-power laser diode, and so on. Qualitative flow structure was acquired by the Schlieren measurement using a high-speed camera and Xenon lamp with a blue optical filter. Simultaneous visualization was achieved 1.6 kfps frame rate and it gave the detailed structure of unsteady flow fields caused by the unsteady shock wave oscillation due to shock-wave/boundary-layer interaction around the juncture between cone and cylinder on the model. Simultaneous measurement results were merged into a movie including surface pressure distribution on the rocket faring and spatial structure of shock wave system concerning to transonic buffet. Constructed movie gave a timeseries and global information of transonic buffet flow field on the rocket faring model visually.

The effect of tip speed ratio on a vertical axis wind turbine at high Reynolds numbers

NASA Astrophysics Data System (ADS)

Parker, Colin M.; Leftwich, Megan C.

2016-05-01

This work visualizes the flow surrounding a scaled model vertical axis wind turbine at realistic operating conditions. The model closely matches geometric and dynamic properties—tip speed ratio and Reynolds number—of a full-size turbine. The flow is visualized using particle imaging velocimetry (PIV) in the midplane upstream, around, and after (up to 4 turbine diameters downstream) the turbine, as well as a vertical plane behind the turbine. Time-averaged results show an asymmetric wake behind the turbine, regardless of tip speed ratio, with a larger velocity deficit for a higher tip speed ratio. For the higher tip speed ratio, an area of averaged flow reversal is present with a maximum reverse flow of -0.04U_∞. Phase-averaged vorticity fields—achieved by syncing the PIV system with the rotation of the turbine—show distinct structures form from each turbine blade. There were distinct differences in results by tip speed ratios of 0.9, 1.3, and 2.2 of when in the cycle structures are shed into the wake—switching from two pairs to a single pair of vortices being shed—and how they convect into the wake—the middle tip speed ratio vortices convect downstream inside the wake, while the high tip speed ratio pair is shed into the shear layer of the wake. Finally, results show that the wake structure is much more sensitive to changes in tip speed ratio than to changes in Reynolds number.

Interior flow and near-nozzle spray development in a marine-engine diesel fuel injector

NASA Astrophysics Data System (ADS)

Hult, J.; Simmank, P.; Matlok, S.; Mayer, S.; Falgout, Z.; Linne, M.

2016-04-01

A consolidated effort at optically characterising flow patterns, in-nozzle cavitation, and near-nozzle jet structure of a marine diesel fuel injector is presented. A combination of several optical techniques was employed to fully transparent injector models, compound metal-glass and full metal injectors. They were all based on a common real-scale dual nozzle hole geometry for a marine two-stroke diesel engine. In a stationary flow rig, flow velocities in the sac-volume and nozzle holes were measured using PIV, and in-nozzle cavitation visualized using high-resolution shadowgraphs. The effect of varying cavitation number was studied and results compared to CFD predictions. In-nozzle cavitation and near-nozzle jet structure during transient operation were visualized simultaneously, using high-speed imaging in an atmospheric pressure spray rig. Near-nozzle spray formation was investigated using ballistic imaging. Finally, the injector geometry was tested on a full-scale marine diesel engine, where the dynamics of near-nozzle jet development was visualized using high-speed shadowgraphy. The range of studies focused on a single common geometry allows a comprehensive survey of phenomena ranging from first inception of cavitation under well-controlled flow conditions to fuel jet structure at real engine conditions.

TOWARD QUANTITATIVE OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY: Visualizing Blood Flow Speeds in Ocular Pathology Using Variable Interscan Time Analysis.

PubMed

Ploner, Stefan B; Moult, Eric M; Choi, WooJhon; Waheed, Nadia K; Lee, ByungKun; Novais, Eduardo A; Cole, Emily D; Potsaid, Benjamin; Husvogt, Lennart; Schottenhamml, Julia; Maier, Andreas; Rosenfeld, Philip J; Duker, Jay S; Hornegger, Joachim; Fujimoto, James G

2016-12-01

Currently available optical coherence tomography angiography systems provide information about blood flux but only limited information about blood flow speed. The authors develop a method for mapping the previously proposed variable interscan time analysis (VISTA) algorithm into a color display that encodes relative blood flow speed. Optical coherence tomography angiography was performed with a 1,050 nm, 400 kHz A-scan rate, swept source optical coherence tomography system using a 5 repeated B-scan protocol. Variable interscan time analysis was used to compute the optical coherence tomography angiography signal from B-scan pairs having 1.5 millisecond and 3.0 milliseconds interscan times. The resulting VISTA data were then mapped to a color space for display. The authors evaluated the VISTA visualization algorithm in normal eyes (n = 2), nonproliferative diabetic retinopathy eyes (n = 6), proliferative diabetic retinopathy eyes (n = 3), geographic atrophy eyes (n = 4), and exudative age-related macular degeneration eyes (n = 2). All eyes showed blood flow speed variations, and all eyes with pathology showed abnormal blood flow speeds compared with controls. The authors developed a novel method for mapping VISTA into a color display, allowing visualization of relative blood flow speeds. The method was found useful, in a small case series, for visualizing blood flow speeds in a variety of ocular diseases and serves as a step toward quantitative optical coherence tomography angiography.

The Aeroacoustics and Aerodynamics of High-Speed Coanda Devices, Part 1: Conventional Arrangement of Exit Nozzle and Surface

NASA Astrophysics Data System (ADS)

Carpenter, P. W.; Green, P. N.

1997-12-01

The literature on high-speed Coanda flows and its applications is reviewed. The lack of basic information for design engineers is noted. The present paper is based on an investigation of the aeroacoustics and aerodynamics of the high-speed Coanda flow that is formed when a supersonic jet issues from a radial nozzle and adheres to a tulip-shaped body of revolution. Schlieren and other flow visualization techniques together with theoretical methods are used to reveal the various features of this complex flow field. The acoustic characteristics were obtained from measurements with an array of microphones in an anechoic chamber. The emphasis is placed on those features of the aerodynamics and aeroacoustics which may be of general interest.

Visual regulation of ground speed and headwind compensation in freely flying honey bees (Apis mellifera L.).

PubMed

Barron, Andrew; Srinivasan, Mandyam V

2006-03-01

There is now increasing evidence that honey bees regulate their ground speed in flight by holding constant the speed at which the image of the environment moves across the eye (optic flow). We have investigated the extent to which ground speed is affected by headwinds. Honey bees were trained to enter a tunnel to forage at a sucrose feeder placed at its far end. Ground speeds in the tunnel were recorded while systematically varying the visual texture of the tunnel, and the strength of headwinds experienced by the flying bees. We found that in a flight tunnel bees used visual cues to maintain their ground speed, and adjusted their air speed to maintain a constant rate of optic flow, even against headwinds which were, at their strongest, 50% of a bee's maximum recorded forward velocity. Manipulation of the visual texture revealed that headwind is compensated almost fully even when the optic flow cues are very sparse and subtle, demonstrating the robustness of this visual flight control system. We discuss these findings in the context of field observations of flying bees.

Development of a Pulsed Combustion Actuator For High-Speed Flow Control

NASA Technical Reports Server (NTRS)

Cutler, Andrew D.; Beck, B. Terry; Wilkes, Jennifer A.; Drummond, J. Philip; Alderfer, David W.; Danehy, Paul M.

2005-01-01

This paper describes the flow within a prototype actuator, energized by pulsed combustion or detonations, that provides a pulsed jet suitable for flow control in high-speed applications. A high-speed valve, capable of delivering a pulsed stream of reactants a mixture of H2 and air at rates of up to 1500 pulses per second, has been constructed. The reactants burn in a resonant chamber, and the products exit the device as a pulsed jet. High frequency pressure transducers have been used to monitor the pressure fluctuations in the device at various reactant injection frequencies, including both resonant and off-resonant conditions. The combustion chamber has been constructed with windows, and the flow inside it has been visualized using Planar Laser-Induced Fluorescence (PLIF). The pulsed jet at the exit of the device has been observed using schlieren.

Visualization of various working fluids flow regimes in gravity heat pipe

NASA Astrophysics Data System (ADS)

Nemec, Patrik

Heat pipe is device working with phase changes of working fluid inside hermetically closed pipe at specific pressure. The phase changes of working fluid from fluid to vapour and vice versa help heat pipe to transport high heat flux. Amount of heat flux transferred by heat pipe, of course depends on kind of working fluid. The article deal about visualization of various working fluids flow regimes in glass gravity heat pipe by high speed camera and processes casing inside during heat pipe operation. Experiment working fluid flow visualization is performed with two glass heat pipes with different inner diameter (13 mm and 22 mm) filled with water, ethanol and fluorinert FC 72. The working fluid flow visualization explains the phenomena as a working fluid boiling, nucleation of bubbles, and vapour condensation on the wall, vapour and condensate flow interaction, flow down condensate film thickness on the wall occurred during the heat pipe operation.

A high-speed photographic system for flow visualization in a steam turbine

NASA Technical Reports Server (NTRS)

Barna, G. J.

1973-01-01

A photographic system was designed to visualize the moisture flow in a steam turbine. Good performance of the system was verified using dry turbine mockups in which an aerosol spray simulated, in a rough way, the moisture flow in the turbine. Borescopes and fiber-optic light tubes were selected as the general instrumentation approach. High speed motion-picture photographs of the liquid flow over the stator blade surfaces were taken using stroboscopic lighting. Good visualization of the liquid flow was obtained. Still photographs of drops in flight were made using short duration flash sources. Drops with diameters as small as 30 micrometers (0.0012 in.) could be resolved. In addition, motion pictures of a spray of water simulating the spray off the rotor blades and shrouds were taken at normal framing rates. Specially constructed light tubes containing small tungsten-halogen lamps were used. Sixteen millimeter photography was used in all cases. Two potential problems resulting from the two-phase turbine flow (attenuation and scattering of light by the fog present and liquid accumulation on the borescope mirrors) were taken into account in the photographic system design but not evaluated experimentally.

Videos and images from 25 years of teaching compressible flow

NASA Astrophysics Data System (ADS)

Settles, Gary

2008-11-01

Compressible flow is a very visual topic due to refractive optical flow visualization and the public fascination with high-speed flight. Films, video clips, and many images are available to convey this in the classroom. An overview of this material is given and selected examples are shown, drawn from educational films, the movies, television, etc., and accumulated over 25 years of teaching basic and advanced compressible-flow courses. The impact of copyright protection and the doctrine of fair use is also discussed.

Simultaneous high-speed schlieren and OH chemiluminescence imaging in a hybrid rocket combustor at elevated pressures

NASA Astrophysics Data System (ADS)

Miller, Victor; Jens, Elizabeth T.; Mechentel, Flora S.; Cantwell, Brian J.; Stanford Propulsion; Space Exploration Group Team

2014-11-01

In this work, we present observations of the overall features and dynamics of flow and combustion in a slab-type hybrid rocket combustor. Tests were conducted in the recently upgraded Stanford Combustion Visualization Facility, a hybrid rocket combustor test platform capable of generating constant mass-flux flows of oxygen. High-speed (3 kHz) schlieren and OH chemiluminescence imaging were used to visualize the flow. We present imaging results for the combustion of two different fuel grains, a classic, low regression rate polymethyl methacrylate (PMMA), and a high regression rate paraffin, and all tests were conducted in gaseous oxygen. Each fuel grain was tested at multiple free-stream pressures at constant oxidizer mass flux (40 kg/m2s). The resulting image sequences suggest that aspects of the dynamics and scaling of the system depend strongly on both pressure and type of fuel.

Experimental study of thermoacoustic effects on a single plate Part I: Temperature fields

NASA Astrophysics Data System (ADS)

Wetzel, M.; Herman, C.

The thermal interaction between a heated solid plate and the acoustically driven working fluid was investigated by visualizing and quantifying the temperature fields in the neighbourhood of the solid plate. A combination of holographic interferometry and high-speed cinematography was applied in the measurements. A better knowledge of these temperature fields is essential to develop systematic design methodologies for heat exchangers in oscillatory flows. The difference between heat transfer in oscillatory flows with zero mean velocity and steady-state flows is demonstrated in the paper. Instead of heat transfer from a heated solid surface to the colder bulk fluid, the visualized temperature fields indicated that heat was transferred from the working fluid into the stack plate at the edge of the plate. In the experiments, the thermoacoustic effect was visualized through the temperature measurements. A novel evaluation procedure that accounts for the influence of the acoustic pressure variations on the refractive index was applied to accurately reconstruct the high-speed, two-dimensional oscillating temperature distributions.

Flow Visualization Techniques in Wind Tunnel Tests of a Full-Scale F/A-18 Aircraft

NASA Technical Reports Server (NTRS)

Lanser, Wendy R.; Botha, Gavin J.; James, Kevin D.; Bennett, Mark; Crowder, James P.; Cooper, Don; Olson, Lawrence (Technical Monitor)

1994-01-01

The proposed paper presents flow visualization performed during experiments conducted on a full-scale F/A-18 aircraft in the 80- by 120-Foot Wind-Tunnel at NASA Ames Research Center. The purpose of the flow-visualization experiments was to document the forebody and leading edge extension (LEX) vortex interaction along with the wing flow patterns at high angles of attack and low speed high Reynolds number conditions. This investigation used surface pressures in addition to both surface and off-surface flow visualization techniques to examine the flow field on the forebody, canopy, LEXS, and wings. The various techniques used to visualize the flow field were fluorescent tufts, flow cones treated with reflective material, smoke in combination with a laser light sheet, and a video imaging system for three-dimension vortex tracking. The flow visualization experiments were conducted over an angle of attack range from 20 deg to 45 deg and over a sideslip range from -10 deg to 10 deg. The various visualization techniques as well as the pressure distributions were used to understand the flow field structure. The results show regions of attached and separated flow on the forebody, canopy, and wings as well as the vortical flow over the leading-edge extensions. This paper will also present flow visualization comparisons with the F-18 HARV flight vehicle and small-scale oil flows on the F-18.

Minimum viewing angle for visually guided ground speed control in bumblebees.

PubMed

Baird, Emily; Kornfeldt, Torill; Dacke, Marie

2010-05-01

To control flight, flying insects extract information from the pattern of visual motion generated during flight, known as optic flow. To regulate their ground speed, insects such as honeybees and Drosophila hold the rate of optic flow in the axial direction (front-to-back) constant. A consequence of this strategy is that its performance varies with the minimum viewing angle (the deviation from the frontal direction of the longitudinal axis of the insect) at which changes in axial optic flow are detected. The greater this angle, the later changes in the rate of optic flow, caused by changes in the density of the environment, will be detected. The aim of the present study is to examine the mechanisms of ground speed control in bumblebees and to identify the extent of the visual range over which optic flow for ground speed control is measured. Bumblebees were trained to fly through an experimental tunnel consisting of parallel vertical walls. Flights were recorded when (1) the distance between the tunnel walls was either 15 or 30 cm, (2) the visual texture on the tunnel walls provided either strong or weak optic flow cues and (3) the distance between the walls changed abruptly halfway along the tunnel's length. The results reveal that bumblebees regulate ground speed using optic flow cues and that changes in the rate of optic flow are detected at a minimum viewing angle of 23-30 deg., with a visual field that extends to approximately 155 deg. By measuring optic flow over a visual field that has a low minimum viewing angle, bumblebees are able to detect and respond to changes in the proximity of the environment well before they are encountered.

Filming the invisible - time-resolved visualization of compressible flows

NASA Astrophysics Data System (ADS)

Kleine, H.

2010-04-01

Essentially all processes in gasdynamics are invisible to the naked eye as they occur in a transparent medium. The task to observe them is further complicated by the fact that most of these processes are also transient, often with characteristic times that are considerably below the threshold of human perception. Both difficulties can be overcome by combining visualization methods that reveal changes in the transparent medium, and high-speed photography techniques that “stop” the motion of the flow. The traditional approach is to reconstruct a transient process from a series of single images, each taken in a different experiment at a different instant. This approach, which is still widely used today, can only be expected to give reliable results when the process is reproducible. Truly time-resolved visualization, which yields a sequence of flow images in a single experiment, has been attempted for more than a century, but many of the developed camera systems were characterized by a high level of complexity and limited quality of the results. Recent advances in digital high-speed photography have changed this situation and have provided the tools to investigate, with relative ease and in sufficient detail, the true development of a transient flow with characteristic time scales down to one microsecond. This paper discusses the potential and the limitations one encounters when using density-sensitive visualization techniques in time-resolved mode. Several examples illustrate how this approach can reveal and explain a number of previously undetected phenomena in a variety of highly transient compressible flows. It is demonstrated that time-resolved visualization offers numerous advantages which normally outweigh its shortcomings, mainly the often-encountered loss in resolution. Apart from the capability to track the location and/or shape of flow features in space and time, adequate time-resolved visualization allows one to observe the development of deliberately introduced near-isentropic perturbation wavelets. This new diagnostic tool can be used to qualitatively and quantitatively determine otherwise inaccessible thermodynamic properties of a compressible flow.

Tools for 3D scientific visualization in computational aerodynamics

NASA Technical Reports Server (NTRS)

Bancroft, Gordon; Plessel, Todd; Merritt, Fergus; Watson, Val

1989-01-01

The purpose is to describe the tools and techniques in use at the NASA Ames Research Center for performing visualization of computational aerodynamics, for example visualization of flow fields from computer simulations of fluid dynamics about vehicles such as the Space Shuttle. The hardware used for visualization is a high-performance graphics workstation connected to a super computer with a high speed channel. At present, the workstation is a Silicon Graphics IRIS 3130, the supercomputer is a CRAY2, and the high speed channel is a hyperchannel. The three techniques used for visualization are post-processing, tracking, and steering. Post-processing analysis is done after the simulation. Tracking analysis is done during a simulation but is not interactive, whereas steering analysis involves modifying the simulation interactively during the simulation. Using post-processing methods, a flow simulation is executed on a supercomputer and, after the simulation is complete, the results of the simulation are processed for viewing. The software in use and under development at NASA Ames Research Center for performing these types of tasks in computational aerodynamics is described. Workstation performance issues, benchmarking, and high-performance networks for this purpose are also discussed as well as descriptions of other hardware for digital video and film recording.

Surface-Streamline Flow Visualization

NASA Technical Reports Server (NTRS)

Langston, L.; Boyle, M.

1985-01-01

Matrix of ink dots covers matte surface of polyester drafting film. Film placed against wind-tunnel wall. Layer of methyl salicylate (oil of wintergreen) sprayed over dotted area. Ink dot streaklines show several characteristics of flow, including primary saddle point of separations, primary horseshoe vortex and smaller vortex at cylinder/ endwall junction. Surface streamline flow visualization technique suitable for use in low-speed windtunnels or other low-speed gas flows.

Three-Dimensional Interactions and Vortical Flows with Emphasis on High Speeds

DTIC Science & Technology

1980-07-01

experimental studies ui.ilizing oil-streak flow-visualization techniques. If a flow-visualization -indicator on a wind-tunnel model is very thin, it has...present study . At a saddle point ’Fig. 10c), there are only two particular lines, CC and DD, that pass through the singular point. The directions on ... case the vortex filament emanating from the focus remains distinct ("tornado-like") and is sean as a separate entity on crossflow planes downstream

An experimental facility for the visual study of turbulent flows.

NASA Technical Reports Server (NTRS)

Brodkey, R. S.; Hershey, H. C.; Corino, E. R.

1971-01-01

An experimental technique which allows visual observations of the wall area in turbulent pipe flow is described in detail. It requires neither the introduction of any injection or measuring device into the flow nor the presence of a two-phase flow or of a non-Newtonian fluid. The technique involves suspending solid MgO particles of colloidal size in trichloroethylene and photographing their motions near the wall with a high speed movie camera moving with the flow. Trichloroethylene was chosen in order to eliminate the index of refraction problem in a curved wall. Evaluation of the technique including a discussion of limitations is included. Also the technique is compared with previous methods of visual observations of turbulent flow.

How humans use visual optic flow to regulate stepping during walking.

PubMed

Salinas, Mandy M; Wilken, Jason M; Dingwell, Jonathan B

2017-09-01

Humans use visual optic flow to regulate average walking speed. Among many possible strategies available, healthy humans walking on motorized treadmills allow fluctuations in stride length (L n ) and stride time (T n ) to persist across multiple consecutive strides, but rapidly correct deviations in stride speed (S n =L n /T n ) at each successive stride, n. Several experiments verified this stepping strategy when participants walked with no optic flow. This study determined how removing or systematically altering optic flow influenced peoples' stride-to-stride stepping control strategies. Participants walked on a treadmill with a virtual reality (VR) scene projected onto a 3m tall, 180° semi-cylindrical screen in front of the treadmill. Five conditions were tested: blank screen ("BLANK"), static scene ("STATIC"), or moving scene with optic flow speed slower than ("SLOW"), matched to ("MATCH"), or faster than ("FAST") walking speed. Participants took shorter and faster strides and demonstrated increased stepping variability during the BLANK condition compared to the other conditions. Thus, when visual information was removed, individuals appeared to walk more cautiously. Optic flow influenced both how quickly humans corrected stride speed deviations and how successful they were at enacting this strategy to try to maintain approximately constant speed at each stride. These results were consistent with Weber's law: healthy adults more-rapidly corrected stride speed deviations in a no optic flow condition (the lower intensity stimuli) compared to contexts with non-zero optic flow. These results demonstrate how the temporal characteristics of optic flow influence ability to correct speed fluctuations during walking. Copyright © 2017 Elsevier B.V. All rights reserved.

Selective Use of Optical Variables to Control Forward Speed

NASA Technical Reports Server (NTRS)

Johnson, Walter W.; Awe, Cynthia A.; Hart, Sandra G. (Technical Monitor)

1994-01-01

Previous work on the perception and control of simulated vehicle speed has examined the contributions of optical flow rate (angular visual speed) and texture, or edge rate (frequency of passing terrain objects or markings) on the perception and control of forward speed. However, these studies have not examined the ability to selectively use edge rate or flow rate. The two studies reported here show that subjects found it very difficult to arbitrarily direct attention to one or the other of these variables; but that the ability to selectively use these variables is linked to the visual contextual information about the relative validity (linkage with speed) of the two variables. The selectivity also resulted in different velocity adaptation levels for events in which flow rate and edge rate specified forward speed. Finally, the role of visual context in directing attention was further buttressed by the finding that the incorrect perception of changes in ground texture density tended to be coupled with incorrect perceptions of changes in forward speed.

Study on Fins' Effect of Boiling Flow in Millimeter Channel Heat Exchanger

NASA Astrophysics Data System (ADS)

Watanabe, Satoshi

2005-11-01

Recently, a lot of researches about compact heat exchangers with mini-channels have been carried out with the hope of obtaining a high-efficiency heat transfer, due to the higher ratio of surface area than existing heat exchangers. However, there are many uncertain phenomena in fields such as boiling flow in mini-channels. Thus, in order to understand the boiling flow in mini-channels to design high-efficiency heat exchangers, this work focused on the visualization measurement of boiling flow in a millimeter channel. A transparent acrylic channel (heat exchanger form), high-speed camera (2000 fps at 1024 x 1024 pixels), and halogen lamp (backup light) were used as the visualization system. The channel's depth is 2 mm, width is 30 mm, and length is 400 mm. In preparation for commercial use, two types of channels were experimented on: a fins type and a normal slit type (without fins). The fins are circular cylindrical obstacles (diameter is 5 mm) to promote heat transfer, set in a triangular array (distance between each center point is 10 mm). Especially in this work, boiling flow and heat transfer promotion in the millimeter channel heat exchanger with fins was evaluated using a high-speed camera.

Vortex rope instabilities in a model of conical draft tube

NASA Astrophysics Data System (ADS)

Skripkin, Sergey; Tsoy, Mikhail; Kuibin, Pavel; Shtork, Sergey

2017-10-01

We report on experimental studies of the formation of vortex ropes in a laboratory simplified model of hydroturbine draft tube. Work is focused on the observation of various flow patterns at the different rotational speed of turbine runner at fixed flow rate. The measurements involve high-speed visualization and pressure pulsations recordings. Draft tube wall pressure pulsations are registered by pressure transducer for different flow regimes. Vortex rope precession frequency were calculated using FFT transform. The experiments showed interesting features of precessing vortex rope like twin spiral and formation of vortex ring.

Effect of travel speed on the visual control of steering toward a goal.

PubMed

Chen, Rongrong; Niehorster, Diederick C; Li, Li

2018-03-01

Previous studies have proposed that people can use visual cues such as the instantaneous direction (i.e., heading) or future path trajectory of travel specified by optic flow or target visual direction in egocentric space to steer or walk toward a goal. In the current study, we examined what visual cues people use to guide their goal-oriented locomotion and whether their reliance on such visual cues changes as travel speed increases. We presented participants with optic flow displays that simulated their self-motion toward a target at various travel speeds under two viewing conditions in which we made target egocentric direction available or unavailable for steering. We found that for both viewing conditions, participants did not steer along a curved path toward the target such that the actual and the required path curvature to reach the target would converge when approaching the target. At higher travel speeds, participants showed a faster and larger reduction in target-heading angle and more accurate and precise steady-state control of aligning their heading specified by optic flow with the target. These findings support the claim that people use heading and target egocentric direction but not path for goal-oriented locomotion control, and their reliance on heading increases at higher travel speeds. The increased reliance on heading for goal-oriented locomotion control could be due to an increased reliability in perceiving heading from optic flow as the magnitude of flow increases with travel speed. (PsycINFO Database Record (c) 2018 APA, all rights reserved).

Flow visualization of unsteady phenomena in the hypersonic regime using high-speed video camera

NASA Astrophysics Data System (ADS)

Hashimoto, Tokitada; Saito, Tsutomu; Takayama, Kazuyoshi

2004-02-01

Flows over double cones and wedges featured with a large shock induced separation zone are representative of many parts of hypersonic vehicle geometries. To be practically important at shock interactions is phenomena that the shock wave produced from another objects carries out incidence to bow shock around a blunt body in the hypersonic flows, the two shock waves interact each other and various shock interactions occur according to the intensity of the shock wave and depending on the case of the local maximum of pressure and heat flux is locally produced on the body surface. The six types of shock interactions are classified, and particularly in the Type IV, a shear layer generated from the intersection of the two shock reached on the body surface, and locally anomalous pressure increase and aerodynamic heating occurred experimentally. In the present study, unsteady shock oscillations and periodically separation flows were visualized by means of high-speed video camera. Particularly, sequential observations with combination of schlieren methods are very effective because of flow unsteadiness.

An experimental investigation of vortex breakdown on a delta wing

NASA Technical Reports Server (NTRS)

Payne, F. M.; Nelson, R. C.

1986-01-01

An experimental investigation of vortex breakdown on delta wings at high angles is presented. Thin delta wings having sweep angles of 70, 75, 80 and 85 degrees are being studied. Smoke flow visualization and the laser light sheet technique are being used to obtain cross-sectional views of the leading edge vortices as they break down. At low tunnel speeds (as low as 3 m/s) details of the flow, which are usually imperceptible or blurred at higher speeds, can be clearly seen. A combination of lateral and longitudinal cross-sectional views provides information on the three dimensional nature of the vortex structure before, during and after breakdown. Whereas details of the flow are identified in still photographs, the dynamic characteristics of the breakdown process were recorded using high speed movies. Velocity measurements were obtained using a laser Doppler anemometer with the 70 degree delta wing at 30 degrees angle of attack. The measurements show that when breakdown occurs the core flow transforms from a jet-like flow to a wake-like flow.

Background-Oriented Schlieren for Large-Scale and High-Speed Aerodynamic Phenomena

NASA Technical Reports Server (NTRS)

Mizukaki, Toshiharu; Borg, Stephen; Danehy, Paul M.; Murman, Scott M.; Matsumura, Tomoharu; Wakabayashi, Kunihiko; Nakayama, Yoshio

2015-01-01

Visualization of the flow field around a generic re-entry capsule in subsonic flow and shock wave visualization with cylindrical explosives have been conducted to demonstrate sensitivity and applicability of background-oriented schlieren (BOS) for field experiments. The wind tunnel experiment suggests that BOS with a fine-pixel imaging device has a density change detection sensitivity on the order of 10(sup -5) in subsonic flow. In a laboratory setup, the structure of the shock waves generated by explosives have been successfully reconstructed by a computed tomography method combined with BOS.

Wind tunnel investigation of vortex flows on F/A-18 configuration at subsonic through transonic speed

NASA Technical Reports Server (NTRS)

Erickson, Gary E.

1991-01-01

A wind tunnel experiment was conducted in the David Taylor Research Center 7- by 10-Foot Transonic Tunnel of the wing leading-edge extension (LEX) and forebody vortex flows at subsonic and transonic speeds about a 0.06-scale model of the F/A-18. The primary goal was to improve the understanding and control of the vortical flows, including the phenomena of vortex breakdown and vortex interactions with the vertical tails. Laser vapor screen flow visualizations, LEX, and forebody surface static pressures, and six-component forces and moments were obtained at angles of attack of 10 to 50 degrees, free-stream Mach numbers of 0.20 to 0.90, and Reynolds numbers based on the wing mean aerodynamic chord of 0.96 x 10(exp 6) to 1.75 x 10(exp 6). The wind tunnel results were correlated with in-flight flow visualizations and handling qualities trends obtained by NASA using an F-18 High-Alpha Research Vehicle (HARV) and by the Navy and McDonnell Douglas on F-18 aircraft with LEX fences added to improve the vertical tail buffet environment. Key issues that were addressed include the sensitivity of the vortical flows to the Reynolds number and Mach number; the reduced vertical tail excitation, and the corresponding flow mechanism, in the presence of the LEX fence; the repeatability of data obtained during high angle-of-attack wind tunnel testing of F-18 models; the effects of particle seeding for flow visualization on the quantitative model measurements; and the interpretation of off-body flow visualizations obtained using different illumination and particle seeding techniques.

Schlieren visualization of flow-field modification over an airfoil by near-surface gas-density perturbations generated by a nanosecond-pulse-driven plasma actuator

NASA Astrophysics Data System (ADS)

Komuro, Atsushi; Takashima, Keisuke; Konno, Kaiki; Tanaka, Naoki; Nonomura, Taku; Kaneko, Toshiro; Ando, Akira; Asai, Keisuke

2017-06-01

Gas-density perturbations near an airfoil surface generated by a nanosecond dielectric-barrier-discharge plasma actuator (ns-DBDPA) are visualized using a high-speed Schlieren imaging method. Wind-tunnel experiments are conducted for a wind speed of 20 m s-1 with an NACA0015 airfoil whose chord length is 100 mm. The results show that the ns-DBDPA first generates a pressure wave and then stochastic perturbations of the gas density near the leading edge of the airfoil. Two structures with different characteristics are observed in the stochastic perturbations. One structure propagates along the boundary between the shear layer and the main flow at a speed close to that of the main flow. The other propagates more slowly on the surface of the airfoil and causes mixing between the main and shear flows. It is observed that these two heated structures interact with each other, resulting in a recovery in the negative pressure coefficient at the leading edge of the airfoil.

Physics on Tap

ERIC Educational Resources Information Center

Wheeler, Andrew P. S.

2012-01-01

This article aims to describe how to visualize surface tension effects in liquid jets. A simple experiment is proposed using the liquid jet flow from a mains water tap/faucet. Using a modern digital camera with a high shutter speed, it is possible to visualize the instabilities (capillary waves) that form within the jet due to the action of…

NASA low-speed centrifugal compressor for 3-D viscous code assessment and fundamental flow physics research

NASA Technical Reports Server (NTRS)

Hathaway, M. D.; Wood, J. R.; Wasserbauer, C. A.

1991-01-01

A low speed centrifugal compressor facility recently built by the NASA Lewis Research Center is described. The purpose of this facility is to obtain detailed flow field measurements for computational fluid dynamic code assessment and flow physics modeling in support of Army and NASA efforts to advance small gas turbine engine technology. The facility is heavily instrumented with pressure and temperature probes, both in the stationary and rotating frames of reference, and has provisions for flow visualization and laser velocimetry. The facility will accommodate rotational speeds to 2400 rpm and is rated at pressures to 1.25 atm. The initial compressor stage being tested is geometrically and dynamically representative of modern high-performance centrifugal compressor stages with the exception of Mach number levels. Preliminary experimental investigations of inlet and exit flow uniformly and measurement repeatability are presented. These results demonstrate the high quality of the data which may be expected from this facility. The significance of synergism between computational fluid dynamic analysis and experimentation throughout the development of the low speed centrifugal compressor facility is demonstrated.

The selective use of functional optical variables in the control of forward speed

NASA Technical Reports Server (NTRS)

Johnson, Walter W.; Awe, Cynthia A.

1994-01-01

Previous work on the perception and control of simulated vehicle speed has examined the contributions of optical flow rate (angular visual speed) and texture, or edge rate (frequency of passing terrain objects or markings) on the perception and control of forward speed. However, these studies have not examined the ability to selectively use edge rate or flow rate. The two studies presented here show that this ability is far greater for pilots than non-pilots, as would be expected since pilots must control vehicular speed over a variety of altitudes where flow rates change independently of forward speed. These studies also show that this ability to selectively use these variables is linked to the visual contextual information about the relative validity (linkage with speed) of the two variables. Subjective judgment data also indicated that awareness of altitude and ground texture density did not mediate ground speed awareness.

Off-surface infrared flow visualization

NASA Technical Reports Server (NTRS)

Manuel, Gregory S. (Inventor); Obara, Clifford J. (Inventor); Daryabeigi, Kamran (Inventor); Alderfer, David W. (Inventor)

1993-01-01

A method for visualizing off-surface flows is provided. The method consists of releasing a gas with infrared absorbing and emitting characteristics into a fluid flow and imaging the flow with an infrared imaging system. This method allows for visualization of off-surface fluid flow in-flight. The novelty of this method is found in providing an apparatus for flow visualization which is contained within the aircraft so as not to disrupt the airflow around the aircraft, is effective at various speeds and altitudes, and is longer-lasting than previous methods of flow visualization.

Geometric Optimization for Non-Thrombogenicity of a Centrifugal Blood Pump through Flow Visualization

NASA Astrophysics Data System (ADS)

Toyoda, Masahiro; Nishida, Masahiro; Maruyama, Osamu; Yamane, Takashi; Tsutsui, Tatsuo; Sankai, Yoshiyuki

A monopivot centrifugal blood pump, whose impeller is supported with a pivot bearing and a passive magnetic bearing, is under development for implantable artificial heart. The hemolysis level is less than that of commercial centrifugal pumps and the pump size is as small as 160 mL in volume. To solve a problem of thrombus caused by fluid dynamics, flow visualization experiments and animal experiments have been undertaken. For flow visualization a three-fold scale-up model, high-speed video system, and particle tracking velocimetry software were used. To verify non-thrombogenicity one-week animal experiments were conducted with sheep. The initially observed thrombus around the pivot was removed through unifying the separate washout holes to a small centered hole to induce high shear around the pivot. It was found that the thrombus contours corresponded to the shear rate of 300s-1 for red thrombus and 1300-1700s-1 for white thrombus, respectively. Thus flow visualization technique was found to be a useful tool to predict thrombus location.

Vortex shedding within laminar separation bubbles forming over an airfoil

NASA Astrophysics Data System (ADS)

Kirk, Thomas M.; Yarusevych, Serhiy

2017-05-01

Vortex shedding within laminar separation bubbles forming over the suction side of a NACA 0018 airfoil is studied through a combination of high-speed flow visualization and boundary layer measurements. Wind tunnel experiments are performed at a chord-based Reynolds number of 100,000 and four angles of attack. The high-speed flow visualization is complemented by quantitative velocity and surface pressure measurements. The structures are shown to originate from the natural amplification of small-amplitude disturbances, and the shear layer roll-up is found to occur coherently across the span. However, significant cycle-to-cycle variations are observed in vortex characteristics, including shedding period and roll-up location. The formation of the roll-up vortices precedes the later stages of transition, during which these structures undergo significant deformations and breakdown to smaller scales. During this stage of flow development, vortex merging is also observed. The results provide new insight into the development of coherent structures in separation bubbles and their relation to the overall bubble dynamics and mean bubble topology.

Synchronization trigger control system for flow visualization

NASA Technical Reports Server (NTRS)

Chun, K. S.

1987-01-01

The use of cinematography or holographic interferometry for dynamic flow visualization in an internal combustion engine requires a control device that globally synchronizes camera and light source timing at a predefined shaft encoder angle. The device is capable of 0.35 deg resolution for rotational speeds of up to 73 240 rpm. This was achieved by implementing the shaft encoder signal addressed look-up table (LUT) and appropriate latches. The developed digital signal processing technique achieves 25 nsec of high speed triggering angle detection by using direct parallel bit comparison of the shaft encoder digital code with a simulated angle reference code, instead of using angle value comparison which involves more complicated computation steps. In order to establish synchronization to an AC reference signal whose magnitude is variant with the rotating speed, a dynamic peak followup synchronization technique has been devised. This method scrutinizes the reference signal and provides the right timing within 40 nsec. Two application examples are described.

Visual control of flight speed in Drosophila melanogaster.

PubMed

Fry, Steven N; Rohrseitz, Nicola; Straw, Andrew D; Dickinson, Michael H

2009-04-01

Flight control in insects depends on self-induced image motion (optic flow), which the visual system must process to generate appropriate corrective steering maneuvers. Classic experiments in tethered insects applied rigorous system identification techniques for the analysis of turning reactions in the presence of rotating pattern stimuli delivered in open-loop. However, the functional relevance of these measurements for visual free-flight control remains equivocal due to the largely unknown effects of the highly constrained experimental conditions. To perform a systems analysis of the visual flight speed response under free-flight conditions, we implemented a 'one-parameter open-loop' paradigm using 'TrackFly' in a wind tunnel equipped with real-time tracking and virtual reality display technology. Upwind flying flies were stimulated with sine gratings of varying temporal and spatial frequencies, and the resulting speed responses were measured from the resulting flight speed reactions. To control flight speed, the visual system of the fruit fly extracts linear pattern velocity robustly over a broad range of spatio-temporal frequencies. The speed signal is used for a proportional control of flight speed within locomotor limits. The extraction of pattern velocity over a broad spatio-temporal frequency range may require more sophisticated motion processing mechanisms than those identified in flies so far. In Drosophila, the neuromotor pathways underlying flight speed control may be suitably explored by applying advanced genetic techniques, for which our data can serve as a baseline. Finally, the high-level control principles identified in the fly can be meaningfully transferred into a robotic context, such as for the robust and efficient control of autonomous flying micro air vehicles.

Visualization of fluid dynamics at NASA Ames

NASA Technical Reports Server (NTRS)

Watson, Val

1989-01-01

The hardware and software currently used for visualization of fluid dynamics at NASA Ames is described. The software includes programs to create scenes (for example particle traces representing the flow over an aircraft), programs to interactively view the scenes, and programs to control the creation of video tapes and 16mm movies. The hardware includes high performance graphics workstations, a high speed network, digital video equipment, and film recorders.

Accuracy and Tuning of Flow Parsing for Visual Perception of Object Motion During Self-Motion

PubMed Central

Niehorster, Diederick C.

2017-01-01

How do we perceive object motion during self-motion using visual information alone? Previous studies have reported that the visual system can use optic flow to identify and globally subtract the retinal motion component resulting from self-motion to recover scene-relative object motion, a process called flow parsing. In this article, we developed a retinal motion nulling method to directly measure and quantify the magnitude of flow parsing (i.e., flow parsing gain) in various scenarios to examine the accuracy and tuning of flow parsing for the visual perception of object motion during self-motion. We found that flow parsing gains were below unity for all displays in all experiments; and that increasing self-motion and object motion speed did not alter flow parsing gain. We conclude that visual information alone is not sufficient for the accurate perception of scene-relative motion during self-motion. Although flow parsing performs global subtraction, its accuracy also depends on local motion information in the retinal vicinity of the moving object. Furthermore, the flow parsing gain was constant across common self-motion or object motion speeds. These results can be used to inform and validate computational models of flow parsing. PMID:28567272

DOE Office of Scientific and Technical Information (OSTI.GOV)

Balakumar, B J; Chavez - Alarcon, Ramiro; Shu, Fangjun

The aerodynamics of a flight-worthy, radio controlled ornithopter is investigated using a combination of Particle-Image Velocimetry (PIV), load cell measurements, and high-speed photography of smoke visualizations. The lift and thrust forces of the ornithopter are measured at various flow speeds, flapping frequencies and angles of attack to characterize the flight performance. These direct force measurements are then compared with forces estimated using control volume analysis on PIV data. High-speed photography of smoke streaks is used to visualize the evolution of leading edge vortices, and to qualitatively infer the effect of wing deformation on the net downwash. Vortical structures in themore » wake are compared to previous studies on root flapping, and direct measurements of flapping efficiency are used to argue that the current ornithopter operates sub-optimally in converting the input energy into propulsive work.« less

Matching optical flow to motor speed in virtual reality while running on a treadmill.

PubMed

Caramenti, Martina; Lafortuna, Claudio L; Mugellini, Elena; Abou Khaled, Omar; Bresciani, Jean-Pierre; Dubois, Amandine

2018-01-01

We investigated how visual and kinaesthetic/efferent information is integrated for speed perception in running. Twelve moderately trained to trained subjects ran on a treadmill at three different speeds (8, 10, 12 km/h) in front of a moving virtual scene. They were asked to match the visual speed of the scene to their running speed-i.e., treadmill's speed. For each trial, participants indicated whether the scene was moving slower or faster than they were running. Visual speed was adjusted according to their response using a staircase until the Point of Subjective Equality (PSE) was reached, i.e., until visual and running speed were perceived as equivalent. For all three running speeds, participants systematically underestimated the visual speed relative to their actual running speed. Indeed, the speed of the visual scene had to exceed the actual running speed in order to be perceived as equivalent to the treadmill speed. The underestimation of visual speed was speed-dependent, and percentage of underestimation relative to running speed ranged from 15% at 8km/h to 31% at 12km/h. We suggest that this fact should be taken into consideration to improve the design of attractive treadmill-mediated virtual environments enhancing engagement into physical activity for healthier lifestyles and disease prevention and care.

Effects of Passive Porosity on Interacting Vortex Flows At Supersonic Speeds

NASA Technical Reports Server (NTRS)

Erickson, Gary E.

2000-01-01

A wind tunnel experiment was conducted in the NASA Langley Research Center (LaRC) Unitary Plan Wind Tunnel (UPWT) to determine the effects of passive surface porosity on vortex flow interaction about a general research fighter configuration at supersonic speeds. Optical flow measurement and flow visualization techniques were used and included pressure-sensitive paint (PSP), schlieren, and laser vapor screen (LVS) These techniques were combined with force and moment and conventional electronically-scanned pressure (ESP) measurements to quantify and to visualize the effects of flow-through porosity applied to a wing leading-edge extension (LEX) mounted to a 65 deg cropped delta wing model.

Matching optical flow to motor speed in virtual reality while running on a treadmill

PubMed Central

Lafortuna, Claudio L.; Mugellini, Elena; Abou Khaled, Omar

2018-01-01

We investigated how visual and kinaesthetic/efferent information is integrated for speed perception in running. Twelve moderately trained to trained subjects ran on a treadmill at three different speeds (8, 10, 12 km/h) in front of a moving virtual scene. They were asked to match the visual speed of the scene to their running speed–i.e., treadmill’s speed. For each trial, participants indicated whether the scene was moving slower or faster than they were running. Visual speed was adjusted according to their response using a staircase until the Point of Subjective Equality (PSE) was reached, i.e., until visual and running speed were perceived as equivalent. For all three running speeds, participants systematically underestimated the visual speed relative to their actual running speed. Indeed, the speed of the visual scene had to exceed the actual running speed in order to be perceived as equivalent to the treadmill speed. The underestimation of visual speed was speed-dependent, and percentage of underestimation relative to running speed ranged from 15% at 8km/h to 31% at 12km/h. We suggest that this fact should be taken into consideration to improve the design of attractive treadmill-mediated virtual environments enhancing engagement into physical activity for healthier lifestyles and disease prevention and care. PMID:29641564

The construction and operation of a water tunnel in application to flow visualization studies of an oscillating airfoil

NASA Technical Reports Server (NTRS)

Olsen, J. H.; Liu, H. T.

1973-01-01

The water tunnel which was constructed at the NASA Ames Research Center is described along with the flow field adjacent to an oscillating airfoil. The design and operational procedures of the tunnel are described in detail. Hydrogen bubble and thymol blue techniques are used to visualize the flow field. Results of the flow visualizations are presented in a series of still pictures and a high speed movie. These results show that time stall is more complicated than simple shedding from the leading edge or the trailing edge, particularly at relatively low frequency oscillations comparable to those of a helicopter blade. Therefore, any successful theory for predicting the stall loads on the helicopter blades must treat an irregular separated region rather than a discrete vortex passing over each blade surface.

Synchronizing Photography For High-Speed-Engine Research

NASA Technical Reports Server (NTRS)

Chun, K. S.

1989-01-01

Light flashes when shaft reaches predetermined angle. Synchronization system facilitates visualization of flow in high-speed internal-combustion engines. Designed for cinematography and holographic interferometry, system synchronizes camera and light source with predetermined rotational angle of engine shaft. 10-bit resolution of absolute optical shaft encoder adapted, and 2 to tenth power combinations of 10-bit binary data computed to corresponding angle values. Pre-computed angle values programmed into EPROM's (erasable programmable read-only memories) to use as angle lookup table. Resolves shaft angle to within 0.35 degree at rotational speeds up to 73,240 revolutions per minute.

Self-synchronizing Schlieren photography and interferometry for the visualization of unsteady transonic flows

NASA Technical Reports Server (NTRS)

Kadlec, R.

1979-01-01

The use of self synchronizing stroboscopic Schlieren and laser interferometer systems to obtain quantitative space time measurements of distinguished flow surfaces, steakline patterns, and the density field of two dimensional flows that exhibit a periodic content was investigated. A large field single path stroboscopic Schlieren system was designed, constructed and successfully applied to visualize four periodic flows: near wake behind an oscillating airfoil; edge tone sound generation; 2-D planar wall jet; and axisymmetric pulsed sonic jet. This visualization technique provides an effective means of studying quasi-periodic flows in real time. The image on the viewing screen is a spatial signal average of the coherent periodic motion rather than a single realization, the high speed motion of a quasi-periodic flow can be reconstructed by recording photographs of the flow at different fixed time delays in one cycle. The preliminary design and construction of a self synchronizing stroboscopic laser interferometer with a modified Mach-Zehnder optical system is also reported.

Neural basis of forward flight control and landing in honeybees.

PubMed

Ibbotson, M R; Hung, Y-S; Meffin, H; Boeddeker, N; Srinivasan, M V

2017-11-06

The impressive repertoire of honeybee visually guided behaviors, and their ability to learn has made them an important tool for elucidating the visual basis of behavior. Like other insects, bees perform optomotor course correction to optic flow, a response that is dependent on the spatial structure of the visual environment. However, bees can also distinguish the speed of image motion during forward flight and landing, as well as estimate flight distances (odometry), irrespective of the visual scene. The neural pathways underlying these abilities are unknown. Here we report on a cluster of descending neurons (DNIIIs) that are shown to have the directional tuning properties necessary for detecting image motion during forward flight and landing on vertical surfaces. They have stable firing rates during prolonged periods of stimulation and respond to a wide range of image speeds, making them suitable to detect image flow during flight behaviors. While their responses are not strictly speed tuned, the shape and amplitudes of their speed tuning functions are resistant to large changes in spatial frequency. These cells are prime candidates not only for the control of flight speed and landing, but also the basis of a neural 'front end' of the honeybee's visual odometer.

Non-Intrusive Optical Diagnostic Methods for Flowfield Characterization

NASA Technical Reports Server (NTRS)

Tabibi, Bagher M.; Terrell, Charles A.; Spraggins, Darrell; Lee, Ja. H.; Weinstein, Leonard M.

1997-01-01

Non-intrusive optical diagnostic techniques such as Electron Beam Fluorescence (EBF), Laser-Induced Fluorescence (LIF), and Focusing Schlieren (FS) have been setup for high-speed flow characterization and large flowfield visualization, respectively. Fluorescence emission from the First Negative band of N2(+) with the (0,0) vibration transition (at lambda =391.44 nm) was obtained using the EBF technique and a quenching rate of N2(+)* molecules by argon gas was reported. A very high sensitivity FS system was built and applied in the High-Speed Flow Generator (HFG) at NASA LaRC. A LIF system is available at the Advanced Propulsion Laboratory (APL) on campus and a plume exhaust velocity measurement, measuring the Doppler shift from lambda = 728.7 nm of argon gas, is under way.

Influence of shock waves from plasma actuators on transonic and supersonic airflow

NASA Astrophysics Data System (ADS)

Mursenkova, I. V.; Znamenskaya, I. A.; Lutsky, A. E.

2018-03-01

This paper presents experimental and numerical investigations of high-current sliding surface discharges of nanosecond duration and their effect on high-speed flow as plasma actuators in a shock tube. This study deals with the effectiveness of a sliding surface discharge at low and medium air pressure. Results cover the electrical characteristics of the discharge and optical visualization of the discharge and high-speed post-discharge flow. A sliding surface discharge is first studied in quiescent air conditions and then in high-speed flow, being initiated in the boundary layer at a transverse flow velocity of 50-950 m s-1 behind a flat shock wave in air of density 0.04-0.45 kg m-3. The discharge is powered by a pulse voltage of 25-30 kV and the electric current is ~0.5 kA. Shadow imaging and particle image velocimetry (PIV) are used to measure the flow field parameters after the pulse surface discharge. Shadow imaging reveals shock waves originating from the channels of the discharge configurations. PIV is used to measure the velocity field resulting from the discharge in quiescent air and to determine the homogeneity of energy release along the sliding discharge channel. Semicylindrical shock waves from the channels of the sliding discharge have an initial velocity of more than 600 m s-1. The shock-wave configuration floats in the flow along the streamlined surface. Numerical simulation based on the equations of hydrodynamics matched with the experiment showed that 25%-50% of the discharge energy is instantly transformed into heat energy in a high-speed airflow, leading to the formation of shock waves. This energy is comparable to the flow enthalpy and can result in significant modification of the boundary layer and the entire flow.

2011 IEEE Visualization Contest winner: Visualizing unsteady vortical behavior of a centrifugal pump.

PubMed

Otto, Mathias; Kuhn, Alexander; Engelke, Wito; Theisel, Holger

2012-01-01

In the 2011 IEEE Visualization Contest, the dataset represented a high-resolution simulation of a centrifugal pump operating below optimal speed. The goal was to find suitable visualization techniques to identify regions of rotating stall that impede the pump's effectiveness. The winning entry split analysis of the pump into three parts based on the pump's functional behavior. It then applied local and integration-based methods to communicate the unsteady flow behavior in different regions of the dataset. This research formed the basis for a comparison of common vortex extractors and more recent methods. In particular, integration-based methods (separation measures, accumulated scalar fields, particle path lines, and advection textures) are well suited to capture the complex time-dependent flow behavior. This video (http://youtu.be/oD7QuabY0oU) shows simulations of unsteady flow in a centrifugal pump.

Fast visual prediction and slow optimization of preferred walking speed.

PubMed

O'Connor, Shawn M; Donelan, J Maxwell

2012-05-01

People prefer walking speeds that minimize energetic cost. This may be accomplished by directly sensing metabolic rate and adapting gait to minimize it, but only slowly due to the compounded effects of sensing delays and iterative convergence. Visual and other sensory information is available more rapidly and could help predict which gait changes reduce energetic cost, but only approximately because it relies on prior experience and an indirect means to achieve economy. We used virtual reality to manipulate visually presented speed while 10 healthy subjects freely walked on a self-paced treadmill to test whether the nervous system beneficially combines these two mechanisms. Rather than manipulating the speed of visual flow directly, we coupled it to the walking speed selected by the subject and then manipulated the ratio between these two speeds. We then quantified the dynamics of walking speed adjustments in response to perturbations of the visual speed. For step changes in visual speed, subjects responded with rapid speed adjustments (lasting <2 s) and in a direction opposite to the perturbation and consistent with returning the visually presented speed toward their preferred walking speed, when visual speed was suddenly twice (one-half) the walking speed, subjects decreased (increased) their speed. Subjects did not maintain the new speed but instead gradually returned toward the speed preferred before the perturbation (lasting >300 s). The timing and direction of these responses strongly indicate that a rapid predictive process informed by visual feedback helps select preferred speed, perhaps to complement a slower optimization process that seeks to minimize energetic cost.

Vapor-screen technique for flow visualization in the Langley Unitary Plan Wind Tunnel

NASA Technical Reports Server (NTRS)

Morris, O. A.; Corlett, W. A.; Wassum, D. L.; Babb, C. D.

1985-01-01

The vapor-screen technique for flow visualization, as developed for the Langley Unitary Plan Wind Tunnel, is described with evaluations of light sources and photographic equipment. Test parameters including dew point, pressure, and temperature were varied to determine optimum conditions for obtaining high-quality vapor-screen photographs. The investigation was conducted in the supersonic speed range for Mach numbers from 1.47 to 4.63 at model angles of attack up to 35 deg. Vapor-screen photographs illustrating various flow patterns are presented for several missile and aircraft configurations. Examples of vapor-screen results that have contributed to the understanding of complex flow fields and provided a basis for the development of theoretical codes are presented with reference to other research.

Visualization of polymer relaxation in viscoelastic turbulent micro-channel flow.

PubMed

Tai, Jiayan; Lim, Chun Ping; Lam, Yee Cheong

2015-11-13

In micro-channels, the flow of viscous liquids e.g. water, is laminar due to the low Reynolds number in miniaturized dimensions. An aqueous solution becomes viscoelastic with a minute amount of polymer additives; its flow behavior can become drastically different and turbulent. However, the molecules are typically invisible. Here we have developed a novel visualization technique to examine the extension and relaxation of polymer molecules at high flow velocities in a viscoelastic turbulent flow. Using high speed videography to observe the fluorescein labeled molecules, we show that viscoelastic turbulence is caused by the sporadic, non-uniform release of energy by the polymer molecules. This developed technique allows the examination of a viscoelastic liquid at the molecular level, and demonstrates the inhomogeneity of viscoelastic liquids as a result of molecular aggregation. It paves the way for a deeper understanding of viscoelastic turbulence, and could provide some insights on the high Weissenberg number problem. In addition, the technique may serve as a useful tool for the investigations of polymer drag reduction.

Visualization of polymer relaxation in viscoelastic turbulent micro-channel flow

NASA Astrophysics Data System (ADS)

Tai, Jiayan; Lim, Chun Ping; Lam, Yee Cheong

2015-11-01

In micro-channels, the flow of viscous liquids e.g. water, is laminar due to the low Reynolds number in miniaturized dimensions. An aqueous solution becomes viscoelastic with a minute amount of polymer additives; its flow behavior can become drastically different and turbulent. However, the molecules are typically invisible. Here we have developed a novel visualization technique to examine the extension and relaxation of polymer molecules at high flow velocities in a viscoelastic turbulent flow. Using high speed videography to observe the fluorescein labeled molecules, we show that viscoelastic turbulence is caused by the sporadic, non-uniform release of energy by the polymer molecules. This developed technique allows the examination of a viscoelastic liquid at the molecular level, and demonstrates the inhomogeneity of viscoelastic liquids as a result of molecular aggregation. It paves the way for a deeper understanding of viscoelastic turbulence, and could provide some insights on the high Weissenberg number problem. In addition, the technique may serve as a useful tool for the investigations of polymer drag reduction.

Visualization of polymer relaxation in viscoelastic turbulent micro-channel flow

PubMed Central

Tai, Jiayan; Lim, Chun Ping; Lam, Yee Cheong

2015-01-01

In micro-channels, the flow of viscous liquids e.g. water, is laminar due to the low Reynolds number in miniaturized dimensions. An aqueous solution becomes viscoelastic with a minute amount of polymer additives; its flow behavior can become drastically different and turbulent. However, the molecules are typically invisible. Here we have developed a novel visualization technique to examine the extension and relaxation of polymer molecules at high flow velocities in a viscoelastic turbulent flow. Using high speed videography to observe the fluorescein labeled molecules, we show that viscoelastic turbulence is caused by the sporadic, non-uniform release of energy by the polymer molecules. This developed technique allows the examination of a viscoelastic liquid at the molecular level, and demonstrates the inhomogeneity of viscoelastic liquids as a result of molecular aggregation. It paves the way for a deeper understanding of viscoelastic turbulence, and could provide some insights on the high Weissenberg number problem. In addition, the technique may serve as a useful tool for the investigations of polymer drag reduction. PMID:26563615

Speed but not amplitude of visual feedback exacerbates force variability in older adults.

PubMed

Kim, Changki; Yacoubi, Basma; Christou, Evangelos A

2018-06-23

Magnification of visual feedback (VF) impairs force control in older adults. In this study, we aimed to determine whether the age-associated increase in force variability with magnification of visual feedback is a consequence of increased amplitude or speed of visual feedback. Seventeen young and 18 older adults performed a constant isometric force task with the index finger at 5% of MVC. We manipulated the vertical (force gain) and horizontal (time gain) aspect of the visual feedback so participants performed the task with the following VF conditions: (1) high amplitude-fast speed; (2) low amplitude-slow speed; (3) high amplitude-slow speed. Changing the visual feedback from low amplitude-slow speed to high amplitude-fast speed increased force variability in older adults but decreased it in young adults (P < 0.01). Changing the visual feedback from low amplitude-slow speed to high amplitude-slow speed did not alter force variability in older adults (P > 0.2), but decreased it in young adults (P < 0.01). Changing the visual feedback from high amplitude-slow speed to high amplitude-fast speed increased force variability in older adults (P < 0.01) but did not alter force variability in young adults (P > 0.2). In summary, increased force variability in older adults with magnification of visual feedback was evident only when the speed of visual feedback increased. Thus, we conclude that in older adults deficits in the rate of processing visual information and not deficits in the processing of more visual information impair force control.

Flow Visualization in Supersonic Turbulent Boundary Layers.

NASA Astrophysics Data System (ADS)

Smith, Michael Wayne

This thesis is a collection of novel flow visualizations of two different flat-plate, zero pressure gradient, supersonic, turbulent boundary layers (M = 2.8, Re _theta ~ 82,000, and M = 2.5, Re_ theta ~ 25,000, respectively). The physics of supersonic shear flows has recently drawn increasing attention with the renewed interest in flight at super and hypersonic speeds. This work was driven by the belief that the study of organized, Reynolds -stress producing turbulence structures will lead to improved techniques for the modelling and control of high-speed boundary layers. Although flow-visualization is often thought of as a tool for providing qualitative information about complex flow fields, in this thesis an emphasis is placed on deriving quantitative results from image data whenever possible. Three visualization techniques were applied--'selective cut-off' schlieren, droplet seeding, and Rayleigh scattering. Two experiments employed 'selective cut-off' schlieren. In the first, high-speed movies (40,000 fps) were made of strong density gradient fronts leaning downstream at between 30^circ and 60^ circ and travelling at about 0.9U _infty. In the second experiment, the same fronts were detected with hot-wires and imaged in real time, thus allowing the examination of the density gradient fronts and their associated single-point mass -flux signals. Two experiments employed droplet seeding. In both experiments, the boundary layer was seeded by injecting a stream of acetone through a single point in the wall. The acetone is atomized by the high shear at the wall into a 'fog' of tiny (~3.5mu m) droplets. In the first droplet experiment, the fog was illuminated with copper-vapor laser sheets of various orientations. The copper vapor laser pulses 'froze' the fog motion, revealing a variety of organized turbulence structures, some with characteristic downstream inclinations, others with large-scale roll-up on the scale of delta. In the second droplet experiment, high-speed movies were made of the fog under general illumination, thus providing information about the streamwise evolution of the structures seen in the planar stills. Rayleigh scattering from a laser sheet was used to create instantaneous density cross-sections in the M = 2.5 boundary layer. The Rayleigh scattering experiment represents the first measurement of the instantaneous 2-D field of an intrinsic fluid property in any boundary layer. Imaged by an intensified UV camera, scattering from the Argon-Fluoride laser (193 nm) revealed density structures with sharp interfaces between high and low-density fluid. These pictures were also used to generated quantitative turbulence information. Density pdf profiles, intermittency values, density correlations, and structure shape data were derived with standard digital image-processing techniques.

Developments in flow visualization methods for flight research

NASA Technical Reports Server (NTRS)

Holmes, Bruce J.; Obara, Clifford J.; Manuel, Gregory S.; Lee, Cynthia C.

1990-01-01

With the introduction of modern airplanes utilizing laminar flow, flow visualization has become an important diagnostic tool in determining aerodynamic characteristics such as surface flow direction and boundary-layer state. A refinement of the sublimating chemical technique has been developed to define both the boundary-layer transition location and the transition mode. In response to the need for flow visualization at subsonic and transonic speeds and altitudes above 20,000 feet, the liquid crystal technique has been developed. A third flow visualization technique that has been used is infrared imaging, which offers non-intrusive testing over a wide range of test conditions. A review of these flow visualization methods and recent flight results is presented for a variety of modern aircraft and flight conditions.

Background-Oriented Schlieren used in a hypersonic inlet test at NASA GRC

NASA Technical Reports Server (NTRS)

Clem, Michelle; Woike, Mark; Saunders, John

2016-01-01

Background Oriented Schlieren (BOS) is a derivative of the classical schlieren technology, which is used to visualize density gradients, such as shock wave structures in a wind tunnel. Changes in refractive index resulting from density gradients cause light rays to bend, resulting in apparent motion of a random background pattern. The apparent motion of the pattern is determined using cross-correlation algorithms (between no-flow and with-flow image pairs) producing a schlieren-like image. One advantage of BOS is its simplified setup which enables a larger field-of-view (FOV) than traditional schlieren systems. In the present study, BOS was implemented into the Combined Cycle Engine Large-Scale Inlet Mode Transition Experiment (CCE LIMX) in the 10x10 Supersonic Wind Tunnel at NASA Glenn Research Center. The model hardware for the CCE LIMX accommodates a fully integrated turbine based combined cycle propulsion system. To date, inlet mode transition between turbine and ramjet operation has been successfully demonstrated. High-speed BOS was used to visualize the behavior of the flow structures shock waves during unsteady inlet unstarts, a phenomenon known as buzz. Transient video images of inlet buzz were recorded for both the ramjet flow path (high speed inlet) and turbine flow path (low speed inlet). To understand the stability limits of the inlet, operation was pushed to the point of unstart and buzz. BOS was implemented in order to view both inlets simultaneously, since the required FOV was beyond the capability of the current traditional schlieren system. An example of BOS data (Images 1-6) capturing inlet buzz are presented.

Hemodynamic flow visualization of early embryonic great vessels using μPIV.

PubMed

Goktas, Selda; Chen, Chia-Yuan; Kowalski, William J; Pekkan, Kerem

2015-01-01

Microparticle image velocimetry (μPIV) is an evolving quantitative methodology to closely and accurately monitor the cardiac flow dynamics and mechanotransduction during vascular morphogenesis. While PIV technique has a long history, contemporary developments in advanced microscopy have significantly expanded its power. This chapter includes three new methods for μPIV acquisition in selected embryonic structures achieved through advanced optical imaging: (1) high-speed confocal scanning of transgenic zebrafish embryos, where the transgenic erythrocytes act as the tracing particles; (2) microinjection of artificial seeding particles in chick embryos visualized with stereomicroscopy; and (3) real-time, time-resolved optical coherence tomography acquisition of vitelline vessel flow profiles in chick embryos, tracking the erythrocytes.

Optic flow-based collision-free strategies: From insects to robots.

PubMed

Serres, Julien R; Ruffier, Franck

2017-09-01

Flying insects are able to fly smartly in an unpredictable environment. It has been found that flying insects have smart neurons inside their tiny brains that are sensitive to visual motion also called optic flow. Consequently, flying insects rely mainly on visual motion during their flight maneuvers such as: takeoff or landing, terrain following, tunnel crossing, lateral and frontal obstacle avoidance, and adjusting flight speed in a cluttered environment. Optic flow can be defined as the vector field of the apparent motion of objects, surfaces, and edges in a visual scene generated by the relative motion between an observer (an eye or a camera) and the scene. Translational optic flow is particularly interesting for short-range navigation because it depends on the ratio between (i) the relative linear speed of the visual scene with respect to the observer and (ii) the distance of the observer from obstacles in the surrounding environment without any direct measurement of either speed or distance. In flying insects, roll stabilization reflex and yaw saccades attenuate any rotation at the eye level in roll and yaw respectively (i.e. to cancel any rotational optic flow) in order to ensure pure translational optic flow between two successive saccades. Our survey focuses on feedback-loops which use the translational optic flow that insects employ for collision-free navigation. Optic flow is likely, over the next decade to be one of the most important visual cues that can explain flying insects' behaviors for short-range navigation maneuvers in complex tunnels. Conversely, the biorobotic approach can therefore help to develop innovative flight control systems for flying robots with the aim of mimicking flying insects' abilities and better understanding their flight. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

NASA Low-Speed Centrifugal Compressor for Fundamental Research

NASA Technical Reports Server (NTRS)

Wood, J. R.; Adam, P. W.; Buggele, A. E.

1983-01-01

A centrifugal compressor facility being built by the NASA Lewis Research Center is described; its purpose is to obtain benchmark experimental data for internal flow code verification and modeling. The facility will be heavily instrumented with standard pressure and temperature probes and have provisions for flow visualization and laser Doppler velocimetry. The facility will accommodate rotational speeds to 2400 rpm and will be rated at pressures to 1.25 atm. The initial compressor stage for testing is geometrically and dynamically representative of modern high-performance stages with the exception of Mach number levels. Design exit tip speed for the initial stage is 500 ft/sec with a pressure ratio of 1.17. The rotor exit backsweep is 55 deg from radial.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kiss, L.I.; Bui, R.T.; Charette, A.

The flow structure inside round furnaces with various numbers of burners, burner arrangement, and exit conditions has been studied experimentally with the purpose of improving the flow conditions and the resulting heat transfer. Small-scale transparent models were built according to the laws of geometric and dynamic similarity. Various visualization and experimental techniques were applied. The flow pattern in the near-surface regions was visualized by the fluorescent minituft and popcorn techniques; the flow structure in the bulk was analyzed by smoke injection and laser sheet illumination. For the study of the transient effects, high-speed video photography was applied. The effects ofmore » the various flow patterns, like axisymmetric and rotational flow, on the magnitude and uniformity of the residence time, as well as on the formation of stagnation zones, were discussed. Conclusions were drawn and have since been applied for the improvement of furnace performance.« less

Flow visualization of CFD using graphics workstations

NASA Technical Reports Server (NTRS)

Lasinski, Thomas; Buning, Pieter; Choi, Diana; Rogers, Stuart; Bancroft, Gordon

1987-01-01

High performance graphics workstations are used to visualize the fluid flow dynamics obtained from supercomputer solutions of computational fluid dynamic programs. The visualizations can be done independently on the workstation or while the workstation is connected to the supercomputer in a distributed computing mode. In the distributed mode, the supercomputer interactively performs the computationally intensive graphics rendering tasks while the workstation performs the viewing tasks. A major advantage of the workstations is that the viewers can interactively change their viewing position while watching the dynamics of the flow fields. An overview of the computer hardware and software required to create these displays is presented. For complex scenes the workstation cannot create the displays fast enough for good motion analysis. For these cases, the animation sequences are recorded on video tape or 16 mm film a frame at a time and played back at the desired speed. The additional software and hardware required to create these video tapes or 16 mm movies are also described. Photographs illustrating current visualization techniques are discussed. Examples of the use of the workstations for flow visualization through animation are available on video tape.

Hot gas ingestion testing of an advanced STOVL concept in the NASA Lewis 9- by 15-foot low speed wind tunnel with flow visualization

NASA Technical Reports Server (NTRS)

Johns, Albert L.; Flood, Joseph D.; Strock, Thomas W.; Amuedo, Kurt C.

1988-01-01

Advanced Short Takeoff/Vertical Landing (STOVL) aircraft capable of operating from remote sites, damaged runways, and small air capable ships are being pursued for deployment around the turn of the century. To achieve this goal, it is important that the technologies critical to this unique class of aircraft be developed. Recognizing this need, NASA Lewis Research Center, McDonnell Douglas Aircraft, and DARPA defined a cooperative program for testing in the NASA Lewis 9- by 15-Foot Low Speed Wind Tunnel (LSWT) to establish a database for hot gas ingestion, one of the technologies critical to STOVL. Results from a test program are presented along with a discussion of the facility modifications allowing this type of testing at model scale. These modifications to the tunnel include a novel ground plane, an elaborate model support which included 4 degrees of freedom, heated high pressure air for nozzle flow, a suction system exhaust for inlet flow, and tunnel sidewall modifications. Several flow visualization techniques were employed including water mist in the nozzle flows and tufts on the ground plane. Headwind (free-stream) velocity was varied from 8 to 23 knots.

Fiber-optic-based laser vapor screen flow visualization system for aerodynamic research in larger scale subsonic and transonic wind tunnels

NASA Technical Reports Server (NTRS)

Erickson, Gary E.; Inenaga, Andrew S.

1994-01-01

Laser vapor screen (LVS) flow visualization systems that are fiber-optic based were developed and installed for aerodynamic research in the Langley 8-Foot Transonic Pressure Tunnel and the Langley 7- by 10-Foot High Speed Tunnel. Fiber optics are used to deliver the laser beam through the plenum shell that surrounds the test section of each facility and to the light-sheet-generating optics positioned in the ceiling window of the test section. Water is injected into the wind tunnel diffuser section to increase the relative humidity and promote condensation of the water vapor in the flow field about the model. The condensed water vapor is then illuminated with an intense sheet of laser light to reveal features of the flow field. The plenum shells are optically sealed; therefore, video-based systems are used to observe and document the flow field. Operational experience shows that the fiber-optic-based systems provide safe, reliable, and high-quality off-surface flow visualization in smaller and larger scale subsonic and transonic wind tunnels. The design, the installation, and the application of the Langley Research Center (LaRC) LVS flow visualization systems in larger scale wind tunnels are highlighted. The efficiency of the fiber optic LVS systems and their insensitivity to wind tunnel vibration, the tunnel operating temperature and pressure variations, and the airborne contaminants are discussed.

Wire-mesh sensor, ultrasound and high-speed videometry applied for the characterization of horizontal gas-liquid slug flow

NASA Astrophysics Data System (ADS)

Ofuchi, C. Y.; Morales, R. E. M.; Arruda, L. V. R.; Neves, F., Jr.; Dorini, L.; do Amaral, C. E. F.; da Silva, M. J.

2012-03-01

Gas-liquid flows occur in a broad range of industrial applications, for instance in chemical, petrochemical and nuclear industries. Correct understating of flow behavior is crucial for safe and optimized operation of equipments and processes. Thus, measurement of gas-liquid flow plays an important role. Many techniques have been proposed and applied to analyze two-phase flows so far. In this experimental research, data from a wire-mesh sensor, an ultrasound technique and high-speed camera are used to study two-phase slug flows in horizontal pipes. The experiments were performed in an experimental two-phase flow loop which comprises a horizontal acrylic pipe of 26 mm internal diameter and 9 m length. Water and air were used to produce the two-phase flow and their flow rates are separately controlled to produce different flow conditions. As a parameter of choice, translational velocity of air bubbles was determined by each of the techniques and comparatively evaluated along with a mechanistic flow model. Results obtained show good agreement among all techniques. The visualization of flow obtained by the different techniques is also presented.

Capillary test specimen, system, and methods for in-situ visualization of capillary flow and fillet formation

DOEpatents

Hall, Aaron C.; Hosking, F. Michael ,; Reece, Mark

2003-06-24

A capillary test specimen, method, and system for visualizing and quantifying capillary flow of liquids under realistic conditions, including polymer underfilling, injection molding, soldering, brazing, and casting. The capillary test specimen simulates complex joint geometries and has an open cross-section to permit easy visual access from the side. A high-speed, high-magnification camera system records the location and shape of the moving liquid front in real-time, in-situ as it flows out of a source cavity, through an open capillary channel between two surfaces having a controlled capillary gap, and into an open fillet cavity, where it subsequently forms a fillet on free surfaces that have been configured to simulate realistic joint geometries. Electric resistance heating rapidly heats the test specimen, without using a furnace. Image-processing software analyzes the recorded images and calculates the velocity of the moving liquid front, fillet contact angles, and shape of the fillet's meniscus, among other parameters.

High angle-of-attack aerodynamic characteristics of crescent and elliptic wings

NASA Technical Reports Server (NTRS)

Vandam, C. P.

1989-01-01

Static longitudinal and lateral-directional forces and moments were measured for elliptic- and crescent-wing models at high angles-of-attack in the NASA Langley 14 by 22-Ft Subsonic Tunnel. The forces and moments were obtained for an angle-of-attack range including stall and post-stall conditions at a Reynolds number based on the average wing chord of about 1.8 million. Flow-visualization photographs using a mixture of oil and titanium-dioxide were also taken for several incidence angles. The force and moment data and the flow-visualization results indicated that the crescent wing model with its highly swept tips produced much better high angle-of-attack aerodynamic characteristics than the elliptic model. Leading-edge separation-induced vortex flow over the highly swept tips of the crescent wing is thought to produce this improved behavior at high angles-of-attack. The unique planform design could result in safer and more efficient low-speed airplanes.

High-Speed PLIF Imaging of Hypersonic Transition over Discrete Cylindrical Roughness

NASA Technical Reports Server (NTRS)

Danehy, P. M.; Ivey, C. B.; Inman, J. A.; Bathel, B. F.; Jones, S. B.; McCrea, A. C.; Jiang, N.; Webster, M.; Lempert, W.; Miller, J.;

Control of Interacting Vortex Flows at Subsonic and Transonic Speeds Using Passive Porosity

NASA Technical Reports Server (NTRS)

Erickson, Gary E.

2003-01-01

A wind tunnel experiment was conducted in the NASA Langley Research Center (LaRC) 8-foot Transonic Pressure Tunnel (TPT) to determine the effects of passive surface porosity on vortex flow interactions about a general research fighter configuration at subsonic and transonic speeds. Flow- through porosity was applied to a wind leading-edge extension (LEX) mounted to a 65 deg cropped delta wind model to promote large nose-down pitching moment increments at high angles of attack. Porosity decreased the vorticity shed from the LEX, which weakened the LEX vortex and altered the global interactions of the LEX and wing vortices at high angles of attack. Six-component forces and moments and wing upper surface static pressure distributions were obtained at free- stream Mach numbers of 0.50, 0.85, and 1.20, Reynolds number of 2.5(10(exp-6) per foot, angles of attack up to 30 deg and angles of sideslip to plus or minus 8 deg. The off-surface flow field was visualized in selected cross-planes using a laser vapor screen flow visualization technique. Test data were obtained with a centerline vertical tail and with alternate twin, wing-mounted vertical fins having 0 deg and 30 deg cant angles. In addition, the porosity of the LEX was compartmentalized to determine the sensitivity of the vortex- dominated aerodynamics to the location and level of porosity applied to the LEX.

Control of Interacting Vortex Flows at Subsonic and Transonic Speeds Using Passive Porosity

NASA Technical Reports Server (NTRS)

Erickson, Gary E.

2003-01-01

A wind tunnel experiment was conducted in the NASA Langley Research Center (LaRC) 8-Foot Transonic Pressure Tunnel (TPT) to determine the effects of passive surface porosity on vortex flow interactions about a general research fighter configuration at subsonic and transonic speeds. Flow-through porosity was applied to a wing leading-edge extension (LEX) mounted to a 65 deg cropped delta wing model to promote large nose-down pitching moment increments at high angles of attack. Porosity decreased the vorticity shed from the LEX, which weakened the LEX vortex and altered the global interactions of the LEX and wing vortices at high angles of attack. Six-component forces and moments and wing upper surface static pressure distributions were obtained at free-stream Mach numbers of 0.50, 0.85, and 1.20, Reynolds number of 2.5(10(exp 6)) per foot, angles of attack up to 30 deg, and angles of sideslip to +/- 8 deg. The off-surface flow field was visualized in selected cross-planes using a laser vapor screen flow visualization technique. Test data were obtained with a centerline vertical tail and with alternate twin, wing-mounted vertical fins having 0 deg and 30 deg cant angles. In addition, the porosity of the LEX was compartmentalized to determine the sensitivity of the vortex-dominated aerodynamics to the location and level of porosity applied to the LEX.

Magnus effects at high angles of attack and critical Reynolds numbers

NASA Technical Reports Server (NTRS)

Seginer, A.; Ringel, M.

1983-01-01

The Magnus force and moment experienced by a yawed, spinning cylinder were studied experimentally in low speed and subsonic flows at high angles of attack and critical Reynolds numbers. Flow-field visualization aided in describing a flow model that divides the Magnus phenomenon into a subcritical region, where reverse Magnus loads are experienced, and a supercritical region where these loads are not encountered. The roles of the spin rate, angle of attack, and crossflow Reynolds number in determining the boundaries of the subcritical region and the variations of the Magnus loads were studied.

Visualization of airflow growing soap bubbles

NASA Astrophysics Data System (ADS)

Al Rahbi, Hamood; Bock, Matthew; Ryu, Sangjin

2016-11-01

Visualizing airflow inside growing soap bubbles can answer questions regarding the fluid dynamics of soap bubble blowing, which is a model system for flows with a gas-liquid-gas interface. Also, understanding the soap bubble blowing process is practical because it can contribute to controlling industrial processes similar to soap bubble blowing. In this study, we visualized airflow which grows soap bubbles using the smoke wire technique to understand how airflow blows soap bubbles. The soap bubble blower setup was built to mimic the human blowing process of soap bubbles, which consists of a blower, a nozzle and a bubble ring. The smoke wire was placed between the nozzle and the bubble ring, and smoke-visualized airflow was captured using a high speed camera. Our visualization shows how air jet flows into the growing soap bubble on the ring and how the airflow interacts with the soap film of growing bubble.

A Visualization Study of Secondary Flows in Cascades

NASA Technical Reports Server (NTRS)

Herzig, Howard Z; Hansen, Arthur G; Costello, George R

1954-01-01

Flow-visualization techniques are employed to ascertain the streamline patterns of the nonpotential secondary flows in the boundary layers of cascades, and thereby to provide a basis for more extended analyses in turbomachines. The three-dimensional deflection of the end-wall boundary layer results in the formation of a vortex within each cascade passage. The size and tightness of the vortex generated depend upon the main-flow turning in the cascade passage. Once formed, a vortex resists turning in subsequent blade rows, with consequent unfavorable angles of attack and possible flow disturbances on the pressure surfaces of subsequent blade rows when the vortices impinge on these surfaces. Two major tip-clearance effects are observed, the formation of a tip-clearance vortex and the scraping effect of a blade with relative motion past the wall boundary layer. The flow patterns indicate methods for improving the blade tip-loading characteristics of compressors and of low- and high-speed turbulence.

The flow of a thin liquid film on a stationary and rotating disk. I - Experimental analysis and flow visualization

NASA Technical Reports Server (NTRS)

Thomas, S.; Faghri, A.; Hankey, W.

1990-01-01

The mean thickness of a thin liquid film of deionized water with a free surface on a stationary and rotating horizontal disk has been measured with a nonobtrusive capacitance technique. The measurements were taken when the rotational speed was 0-300 RPM and the flow rate was 7.0-15.0 LPM. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. When the disk was stationary, a circular hydraulic jump was present on the disk. Surface waves were found in the supercritical and subcritical regions at all flow rates studied. When the rotational speed of the disk is low, a standing wave at the edge of the disk was present. As the rotational speed increased, the surface waves changed from the wavy-laminar region to a region in which the waves ran nearly radially across the disk on top of a thin substrate of fluid.

Effects of optic flow on spontaneous overground walk-to-run transition.

PubMed

De Smet, Kristof; Malcolm, P; Lenoir, M; Segers, V; De Clercq, D

2009-03-01

Perturbations of optic flow can induce changes in walking speed since subjects modulate their speed with respect to the speed perceived from optic flow. The purpose of this study was to examine the effects of optic flow on steady-state as well as on non steady-state locomotion, i.e. on spontaneous overground walk-to-run transitions (WRT) during which subjects were able to accelerate in their preferred way. In this experiment, while subjects moved along a specially constructed hallway, a series of stripes projected on the side walls and ceiling were made to move backward (against the locomotion direction) at an absolute speed of -2 m s(-1) (condition B), or to move forward at an absolute speed of +2 m s(-1) (condition F), or to remain stationary (condition C). While condition B and condition F entailed a decrease and an increase in preferred walking speed, respectively, the spatiotemporal characteristics of the spontaneous walking acceleration prior to reaching WRT were not influenced by modified visual information. However, backward moving stripes induced a smaller speed increase when making the actual transition to running. As such, running speeds after making the WRT were lower in condition B. These results indicate that the walking acceleration prior to reaching the WRT is more robust against visual perturbations compared to walking at preferred walking speed. This could be due to a higher contribution from spinal control during the walking acceleration phase. However, the finding that subjects started to run at a lower running speed when experiencing an approaching optic flow faster than locomotion speed shows that the actual realization of the WRT is not totally independent of external cues.

NASA low-speed centrifugal compressor for fundamental research

NASA Technical Reports Server (NTRS)

Wood, J. R.; Adam, P. W.; Buggele, A. E.

1983-01-01

A new centrifugal compressor facility being built by the NASA Lewis Research Center is described; its purpose is to obtain 'benchmark' experimental data for internal flow code verification and modeling. The facility will be heavily instrumented with standard pressure and temperature probes and have provisions for flow visualization and laser Doppler velocimetry. The facility will accommodate rotational speeds to 2400 rpm and will be rated at pressures to 1.25 atm. The initial compressor stage for testing is geometrically and dynamically representative of modern high-performance stages with the exception of Mach number levels. Design exit tip speed for the initial stage is 500 ft/sec with a pressure ratio of 1.17. The rotor exit backsweep is 55 deg from radial. The facility is expected to be operational in the first half of 1985.

Application of holography to the determination of flow conditions within the rotating blade row of a compressor

NASA Technical Reports Server (NTRS)

Hantman, R. G.; Burr, R. J.; Alwang, W. G.; Williams, M. C.

1973-01-01

The double-pulse, double-exposure holography technique was applied to visualize the flow field within a transonic compressor rotor with a tip speed of 1800 ft/sec. The principal objective was to visualize the shock waves created in the flow field which was supersonic relative to the rotating blade row. The upstream rotor blade bow shocks and, at high speed, the outermost portion of the leading edge passage shock were successfully observed in the holograms. Techniques were devised for locating these shocks in three dimensions, and the results were compared with theoretical predictions. Density changes between the two pulses due to motion of the shocks were large and, therefore, it was not possible to resolve the fringe systems in detail for the 100% speed conditions. However, gross features of the shocks were easily observed, and the upstream shocks were well displayed. In all cases the shock angles were somewhat larger than predicted by theory, and a distinct increase in angle near the outer wall was observed, which may be attributed to endwall boundary layer effects. The location and orientation of the observed leading edge passage shocks were in good agreement with static pressure contours obtained from measurements in the outer casing over the rotor tip.

Does manipulating the speed of visual flow in virtual reality change distance estimation while walking in Parkinson's disease?

PubMed

Ehgoetz Martens, Kaylena A; Ellard, Colin G; Almeida, Quincy J

2015-03-01

Although dopaminergic replacement therapy is believed to improve sensory processing in PD, while delayed perceptual speed is thought to be caused by a predominantly cholinergic deficit, it is unclear whether sensory-perceptual deficits are a result of corrupt sensory processing, or a delay in updating perceived feedback during movement. The current study aimed to examine these two hypotheses by manipulating visual flow speed and dopaminergic medication to examine which influenced distance estimation in PD. Fourteen PD and sixteen HC participants were instructed to estimate the distance of a remembered target by walking to the position the target formerly occupied. This task was completed in virtual reality in order to manipulate the visual flow (VF) speed in real time. Three conditions were carried out: (1) BASELINE: VF speed was equal to participants' real-time movement speed; (2) SLOW: VF speed was reduced by 50 %; (2) FAST: VF speed was increased by 30 %. Individuals with PD performed the experiment in their ON and OFF state. PD demonstrated significantly greater judgement error during BASELINE and FAST conditions compared to HC, although PD did not improve their judgement error during the SLOW condition. Additionally, PD had greater variable error during baseline compared to HC; however, during the SLOW conditions, PD had significantly less variable error compared to baseline and similar variable error to HC participants. Overall, dopaminergic medication did not significantly influence judgement error. Therefore, these results suggest that corrupt processing of sensory information is the main contributor to sensory-perceptual deficits during movement in PD rather than delayed updating of sensory feedback.

Mixing Process in Ejector Nozzles Studied at Lewis' Aero-Acoustic Propulsion Laboratory

NASA Technical Reports Server (NTRS)

1996-01-01

The NASA Lewis Research Center has been studying mixing processes in ejector nozzles for its High Speed Research (HSR) Program. This work is directed at finding ways to minimize the noise of a future supersonic airliner. Much of the noise such an airplane would generate would come from the nozzle, where a hot, high-speed jet exits the engine. Several different nozzle configurations were used to produce nozzle systems with different acoustical and aerodynamic characteristics. The acoustical properties were measured by an array of microphones in an anechoic chamber, and the aerodynamics were measured by traditional pressure and temperature instruments as well as by Laser Doppler Velocimetry (LDV), a technique for visualizing the airflow pattern without disturbing it. These measurements were put together and compared for different configurations to examine the relationships between mixing and noise generation. The mixer-ejector nozzle with the installed flow-visualization windows (foreground), the optical equipment and the supporting structure for the Laser Doppler Velocimetry flow visualization (midfield), and the sound-absorbing wedges used to create an anechoic environment for acoustic testing (background) is shown. The High Speed Research Program is a NASA-funded effort, in cooperation with the U.S. aerospace industry, to develop enabling technologies for a future supersonic airliner. One of the technological barriers being addressed is noise generated during near-airport operation. The mixer-ejector nozzle concept is being examined as a way to reduce jet noise while maintaining thrust. Ambient air is mixed with the high-velocity engine exhaust to reduce the jet velocity and hence the noise generated by the jet. The model was designed and built by Pratt & Whitney under NASA contract. The test, completed in June 1995, was conducted in Lewis' Aero-Acoustic Propulsion Laboratory.

Experimental analysis of the flow pattern of a pump turbine model in pump mode

NASA Astrophysics Data System (ADS)

Guggenberger, Mark; Senn, Florian; Jaberg, Helmut; Gehrer, Arno; Sallaberger, Manfred; Widmer, Christian

2016-11-01

Reversible pump turbines are the only means to store primary energy in an highly efficient way. Within a short time their operation can be switched between the different operational regimes thus enhancing the stabilization of the electric grid. These qualities in combination with the operation even at off-design conditions offer a high flexibility to the energy market. However, pump turbines pass through operational regimes where their behaviour becomes unstable. One of these effects occurs when the flowrate is decreased continuously down to a minimum. This point is the physical limitation of the pump operation and is very difficult to predict properly by numerical design without a model test. The purpose of the present study is to identify the fluid mechanical phenomena leading to the occurrence of instabilities of pump turbines in pump mode. A reduced scale model of a ANDRITZ pump turbine was installed on a 4-quadrant test rig for the experimental investigation of unstable conditions in pump mode. The performed measurements are based on the IEC60193-standard. Characteristic measurements at a single guide vane opening were carried out to get a detailed insight into the instabilities in pump mode. The interaction between runner and guide vane was analysed by Particle Image Velocimetry. Furthermore, high-speed visualizations of the suction side part load flow and the suction recirculation were performed. Like never before the flow pattern in the draft tube cone became visible with the help of a high-speed camera by intentionally caused cavitation effects which allow a qualitative view on the flow pattern in the draft tube cone. Suction recirculation is observed in form of single vortices separating from each runner blade and stretching into the draft tube against the main flow direction. To find an explanation for the flow phenomena responsible for the appearance of the unstable head curve also characteristic velocity distributions on the pressure side were combined with high-speed visualizations on the suction side of the pump turbine model. The results enhance the comprehension of the physical background leading to the instability and improve the numerical predictability of the instability in pump mode.

Engine flow visualization using a copper vapor laser

NASA Technical Reports Server (NTRS)

Regan, Carolyn A.; Chun, Kue S.; Schock, Harold J., Jr.

1987-01-01

A flow visualization system has been developed to determine the air flow within the combustion chamber of a motored, axisymmetric engine. The engine has been equipped with a transparent quartz cylinder, allowing complete optical access to the chamber. A 40-Watt copper vapor laser is used as the light source. Its beam is focused down to a sheet approximately 1 mm thick. The light plane is passed through the combustion chamber, and illuminates oil particles which were entrained in the intake air. The light scattered off of the particles is recorded by a high speed rotating prism movie camera. A movie is then made showing the air flow within the combustion chamber for an entire four-stroke engine cycle. The system is synchronized so that a pulse generated by the camera triggers the laser's thyratron. The camera is run at 5,000 frames per second; the trigger drives one laser pulse per frame. This paper describes the optics used in the flow visualization system, the synchronization circuit, and presents results obtained from the movie. This is believed to be the first published study showing a planar observation of airflow in a four-stroke piston-cylinder assembly. These flow visualization results have been used to interpret flow velocity measurements previously obtained with a laser Doppler velocimetry system.

High-Speed Rainbow Schlieren Visualization of an Oscillating Helium Jet Undergoing Gravitational Change

NASA Technical Reports Server (NTRS)

Leptuch, Peter A.; Agrawal, Ajay K.

2005-01-01

Rainbow schlieren deflectometry combined with high-speed digital imaging was used to study buoyancy effects on flow structure of a helium jet discharged vertically into air. The experimental data were taken using the 2.2-sec drop tower facility at the NASA John H. Glenn Research Center in Cleveland, Ohio. The test conditions pertained to jet Reynolds number of 490 and jet Richardson number of 0.11, for which buoyancy is often considered unimportant. Experimental results show global oscillations at a frequency of 27 Hz in Earth gravity. In microgravity, the jet oscillations vanished and the jet width increased. Results provide a direct physical evidence of the importance of buoyancy on the flow structure of low-density gas jets at a Richardson number considered too small to account for gravity.

FliMax, a novel stimulus device for panoramic and highspeed presentation of behaviourally generated optic flow.

PubMed

Lindemann, J P; Kern, R; Michaelis, C; Meyer, P; van Hateren, J H; Egelhaaf, M

2003-03-01

A high-speed panoramic visual stimulation device is introduced which is suitable to analyse visual interneurons during stimulation with rapid image displacements as experienced by fast moving animals. The responses of an identified motion sensitive neuron in the visual system of the blowfly to behaviourally generated image sequences are very complex and hard to predict from the established input circuitry of the neuron. This finding suggests that the computational significance of visual interneurons can only be assessed if they are characterised not only by conventional stimuli as are often used for systems analysis, but also by behaviourally relevant input.

Horizontal Two Phase Flow Regime Identification: Comparison of Pressure Signature, Electrical Capacitance Tomography (ECT) and High Speed Visualization (Postprint)

DTIC Science & Technology

2012-11-01

W., and Mudawar , I., "Measurement and Correlation of Critical Heat Flux in Two-Phase Micro-Channel Heat Sinks," International Journal of Heat and...Mass Transfer, Vol. 47, No. 10-11, 2004, pp. 2045-2059. 3 Zhang, H., Mudawar , I., and Hasan, M. M., "Photographic Study of High-Flux Subcooled Flow...component Fow in Pipes," Chemical Engineering Progress, Vol. 45, 1949, pp. 39-48. 34 Qu, W., and Mudawar , I., "Measurement and Prediction of Pressure

A visual study of radial inward choked flow of liquid nitrogen.

NASA Technical Reports Server (NTRS)

Hendricks, R. C.; Simoneau, R. J.; Hsu, Y. Y.

1973-01-01

Data and high speed movies were acquired on pressurized subcooled liquid nitrogen flowing radially inward through a 0.0076 cm gap. The stagnation pressure ranged from 0.7 to 4 MN/sq m. Steady radial inward choked flow appears equivalent to steady choked flow through axisymmetric nozzles. Transient choked flows through the radial gap are not uniform and the discharge pattern appears as nonuniform impinging jets. The critical mass flow rate data for the transient case appear different from those for the steady case. On the mass flow rate vs pressure map, the slope and separation of the isotherms appear to be less for transient than for steady radial choked flow.

Heat and mass transfer and hydrodynamics in swirling flows (review)

NASA Astrophysics Data System (ADS)

Leont'ev, A. I.; Kuzma-Kichta, Yu. A.; Popov, I. A.

2017-02-01

Research results of Russian and foreign scientists of heat and mass transfer in whirling flows, swirling effect, superficial vortex generators, thermodynamics and hydrodynamics at micro- and nanoscales, burning at swirl of the flow, and technologies and apparatuses with the use of whirling currents for industry and power generation were presented and discussed at the "Heat and Mass Transfer in Whirling Currents" 5th International Conference. The choice of rational forms of the equipment flow parts when using whirling and swirling flows to increase efficiency of the heat-power equipment and of flow regimes and burning on the basis of deep study of the flow and heat transfer local parameters was set as the main research prospect. In this regard, there is noticeable progress in research methods of whirling and swirling flows. The number of computational treatments of swirling flows' local parameters has been increased. Development and advancement of the up to date computing models and national productivity software are very important for this process. All experimental works are carried out with up to date research methods of the local thermoshydraulic parameters, which enable one to reveal physical mechanisms of processes: PIV and LIV visualization techniques, high-speed and infrared photography, high speed registration of parameters of high-speed processes, etc. There is a problem of improvement of researchers' professional skills in the field of fluid mechanics to set adequately mathematics and physics problems of aerohydrodynamics for whirling and swirling flows and numerical and pilot investigations. It has been pointed out that issues of improvement of the cooling system and thermal protection effectiveness of heat-power and heat-transfer equipment units are still actual. It can be solved successfully using whirling and swirling flows as simple low power consumption exposing on the flow method and heat transfer augmentation.

Experimental parametric study of jet vortex generators for flow separation control

NASA Technical Reports Server (NTRS)

Selby, Gregory

1991-01-01

A parametric wind-tunnel study was performed with jet vortex generators to determine their effectiveness in controlling flow separation associated with low-speed turbulence flow over a two-dimensional rearward-facing ramp. Results indicate that flow-separation control can be accomplished, with the level of control achieved being a function of jet speed, jet orientation (with respect to the free-stream direction), and orifice pattern (double row of jets vs. single row). Compared to slot blowing, jet vortex generators can provide an equivalent level of flow control over a larger spanwise region (for constant jet flow area and speed). Dye flow visualization tests in a water tunnel indicated that the most effective jet vortex generator configurations produced streamwise co-rotating vortices.

Supersonic Coaxial Jet Experiment for CFD Code Validation

NASA Technical Reports Server (NTRS)

Cutler, A. D.; Carty, A. A.; Doerner, S. E.; Diskin, G. S.; Drummond, J. P.

1999-01-01

A supersonic coaxial jet facility has been designed to provide experimental data suitable for the validation of CFD codes used to analyze high-speed propulsion flows. The center jet is of a light gas and the coflow jet is of air, and the mixing layer between them is compressible. Various methods have been employed in characterizing the jet flow field, including schlieren visualization, pitot, total temperature and gas sampling probe surveying, and RELIEF velocimetry. A Navier-Stokes code has been used to calculate the nozzle flow field and the results compared to the experiment.

Visualization of leading edge vortices on a series of flat plate delta wings

NASA Technical Reports Server (NTRS)

Payne, Francis M.; Ng, T. Terry; Nelson, Robert C.

1991-01-01

A summary of flow visualization data obtained as part of NASA Grant NAG2-258 is presented. During the course of this study, many still and high speed motion pictures were taken of the leading edge vortices on a series of flat plate delta wings at varying angles of attack. The purpose is to present a systematic collection of photographs showing the state of vortices as a function of the angle of attack for the four models tested.

A study of high speed flows in an aircraft transition duct. Ph.D. Thesis - Iowa State Univ.

NASA Technical Reports Server (NTRS)

Reichert, Bruce A.

1991-01-01

The study of circular-to-rectangular transition duct flows with and without inlet swirl is presented. A method was devised to create a swirling, solid body rotational flow with minimal associated disturbances. Details of the swirl generator design and construction are discussed. Coefficients based on velocities and total and static pressures measured in cross stream planes at four axial locations within the transition duct along with surface static pressures and surface oil film visualization are presented for both nonswirling and swirling incoming flows. A method was developed to acquire trace gas measurements within the transition duct at high flow velocities. Statistical methods are used to help interpret the trace gas results.

An experimental investigation of a Mach 3.0 high-speed civil transport at supersonic speeds

NASA Technical Reports Server (NTRS)

Hernandez, Gloria; Covell, Peter F.; Mcgraw, Marvin E., Jr.

1993-01-01

An experimental study was conducted to determine the aerodynamic characteristics of a proposed high speed civil transport. This configuration was designed to cruise at Mach 3.0 and sized to carry 250 passengers for 6500 n.mi. The configuration consists of a highly blended wing body and features a blunt parabolic nose planform, a highly swept inboard wing panel, a moderately swept outboard wing panel, and a curved wingtip. Wind tunnel tests were conducted in the Langley Unitary Plan Wind Tunnel on a 0.0098-scale model. Force, moment, and pressure data were obtained for Mach numbers ranging from 1.6 to 3.6 and at angles of attack ranging from -4 to 10 deg. Extensive flow visualization studies (vapor screen and oil flow) were obtained in the experimental program. Both linear and advanced computational fluid dynamics (CFD) theoretical comparisons are shown to assess the ability to predict forces, moments, and pressures on configurations of this type. In addition, an extrapolation of the wind tunnel data, based on empirical principles, to full-scale conditions is compared with the theoretical aerodynamic predictions.

Performance and Near-Wake Flow field of A Marine Hydrokinetic Turbine Operating in Free surface Proximity

NASA Astrophysics Data System (ADS)

Banerjee, Arindam; Kolekar, Nitin

2015-11-01

The current experimental investigation aims at understanding the effect of free surface proximity and associated blockage on near-wake flow-field and performance of a three bladed horizontal axis marine hydrokinetic turbine. Experiments were conducted on a 0.14m radius, three bladed constant chord turbine in a 0.61m ×0.61m test section water channel. The turbine was subjected to various rotational speeds, flow speeds and depths of immersion. Experimental data was acquired through a submerged in-line thrust-torque sensor that was corrected to an unblocked dataset with a blockage correction using measured thrust data. A detailed comparison is presented between blocked and unblocked datasets to identify influence of Reynolds number and free surface proximity on blockage effects. The percent change in Cp was found to be dependent on flow velocity, rotational speed and free surface to blade tip clearance. Further, flow visualization using a stereoscopic particle image velocimetry was carried out in the near-wake region of turbine to understand the mechanism responsible for variation of Cp with rotational speed and free surface proximity. Results revealed presence of slower wake at higher rotational velocities and increased asymmetry in the wake at high free surface proximity.

Local statistics of retinal optic flow for self-motion through natural sceneries.

PubMed

Calow, Dirk; Lappe, Markus

2007-12-01

Image analysis in the visual system is well adapted to the statistics of natural scenes. Investigations of natural image statistics have so far mainly focused on static features. The present study is dedicated to the measurement and the analysis of the statistics of optic flow generated on the retina during locomotion through natural environments. Natural locomotion includes bouncing and swaying of the head and eye movement reflexes that stabilize gaze onto interesting objects in the scene while walking. We investigate the dependencies of the local statistics of optic flow on the depth structure of the natural environment and on the ego-motion parameters. To measure these dependencies we estimate the mutual information between correlated data sets. We analyze the results with respect to the variation of the dependencies over the visual field, since the visual motions in the optic flow vary depending on visual field position. We find that retinal flow direction and retinal speed show only minor statistical interdependencies. Retinal speed is statistically tightly connected to the depth structure of the scene. Retinal flow direction is statistically mostly driven by the relation between the direction of gaze and the direction of ego-motion. These dependencies differ at different visual field positions such that certain areas of the visual field provide more information about ego-motion and other areas provide more information about depth. The statistical properties of natural optic flow may be used to tune the performance of artificial vision systems based on human imitating behavior, and may be useful for analyzing properties of natural vision systems.

Measurement of liquid film flow on nuclear rod bundle in micro-scale by using very high speed camera system

NASA Astrophysics Data System (ADS)

Pham, Son; Kawara, Zensaku; Yokomine, Takehiko; Kunugi, Tomoaki

2012-11-01

Playing important roles in the mass and heat transfer as well as the safety of boiling water reactor, the liquid film flow on nuclear fuel rods has been studied by different measurement techniques such as ultrasonic transmission, conductivity probe, etc. Obtained experimental data of this annular two-phase flow, however, are still not enough to construct the physical model for critical heat flux analysis especially at the micro-scale. Remain problems are mainly caused by complicated geometry of fuel rod bundles, high velocity and very unstable interface behavior of liquid and gas flow. To get over these difficulties, a new approach using a very high speed digital camera system has been introduced in this work. The test section simulating a 3×3 rectangular rod bundle was made of acrylic to allow a full optical observation of the camera. Image data were taken through Cassegrain optical system to maintain the spatiotemporal resolution up to 7 μm and 20 μs. The results included not only the real-time visual information of flow patterns, but also the quantitative data such as liquid film thickness, the droplets' size and speed distributions, and the tilt angle of wavy surfaces. These databases could contribute to the development of a new model for the annular two-phase flow. Partly supported by the Global Center of Excellence (G-COE) program (J-051) of MEXT, Japan.

Hot gas ingestion test results of a two-poster vectored thrust concept with flow visualization in the NASA Lewis 9- x 15-foot low speed wind tunnel

NASA Technical Reports Server (NTRS)

Johns, Albert L.; Neiner, George; Bencic, Timothy J.; Flood, Joseph D.; Amuedo, Kurt C.; Strock, Thomas W.

1990-01-01

A 9.2 percent scale Short Takeoff and Vertical Landing (STOVL) hot gas ingestion model was designed and built by McDonnell Douglas Corporation (MCAIR) and tested in the Lewis Research Center 9 x 15 foot Low Speed Wind Tunnel (LSWT). Hot gas ingestion, the entrainment of heated engine exhaust into the inlet flow field, is a key development issure for advanced short takeoff and vertical landing aircraft. Flow visualization from the Phase 1 test program, which evaluated the hot ingestion phenomena and control techniques, is covered. The Phase 2 test program evaluated the hot gas ingestion phenomena at higher temperatures and used a laser sheet to investigate the flow field. Hot gas ingestion levels were measured for the several forward nozzle splay configurations and with flow control/life improvement devices (LIDs) which reduced the hot gas ingestion. The model support system had four degrees of freedom - pitch, roll, yaw, and vertical height variation. The model support system also provided heated high-pressure air for nozzle flow and a suction system exhaust for inlet flow. The test was conducted at full scale nozzle pressure ratios and inlet Mach numbers. Test and data analysis results from Phase 2 and flow visualization from both Phase 1 and 2 are documented. A description of the model and facility modifications is also provided. Headwind velocity was varied from 10 to 23 kn. Results are presented over a range of nozzle pressure ratios at a 10 kn headwind velocity. The Phase 2 program was conducted at exhaust nozzle temperatures up to 1460 R and utilized a sheet laser system for flow visualization of the model flow field in and out of ground effects. The results reported are for nozzle exhaust temperatures up to 1160 R. These results will contain the compressor face pressure and temperature distortions, the total pressure recovery, the inlet temperature rise, and the environmental effects of the hot gas. The environmental effects include the ground plane contours, the model airframe heating, and the location of the ground flow separation.

Matching visual and nonvisual signals: evidence for a mechanism to discount optic flow during locomotion

NASA Astrophysics Data System (ADS)

Thurrell, Adrian; Pelah, Adar

2005-03-01

We report on recent experiments to investigate the Arthrovisual Locomotor Effect (ALE), a mechanism based on non-visual signals postulated to discount or remove the self-generated visual motion signals during locomotion. It is shown that perceptual matches made by standing subjects to a constant motion optic flow stimulus that is viewed while walking on a treadmill are linearly reduced by walking speed, a measure of the reported ALE. The degree of reduction in perceived speed depends on the similarity of the motor activity to natural locomotion, thus for the four activities tested, ALE strength is ranked as follows: Walking > Cycling > Hand Pedalling > Finger Tapping = 0. Other variations and important controls for the ALE are described.

Ultrasonically Encoded Photoacoustic Flowgraphy in Biological Tissue

NASA Astrophysics Data System (ADS)

Wang, Lidai; Xia, Jun; Yao, Junjie; Maslov, Konstantin I.; Wang, Lihong V.

2013-11-01

Blood flow speed is an important functional parameter. Doppler ultrasound flowmetry lacks sufficient sensitivity to slow blood flow (several to tens of millimeters per second) in deep tissue. To address this challenge, we developed ultrasonically encoded photoacoustic flowgraphy combining ultrasonic thermal tagging with photoacoustic imaging. Focused ultrasound generates a confined heat source in acoustically absorptive fluid. Thermal waves propagate with the flow and are directly visualized in pseudo color using photoacoustic computed tomography. The Doppler shift is employed to calculate the flow speed. This method requires only acoustic and optical absorption, and thus is applicable to continuous fluid. A blood flow speed as low as 0.24mm·s-1 was successfully measured. Deep blood flow imaging was experimentally demonstrated under 5-mm-thick chicken breast tissue.

Assessment of rural soundscapes with high-speed train noise.

PubMed

Lee, Pyoung Jik; Hong, Joo Young; Jeon, Jin Yong

2014-06-01

In the present study, rural soundscapes with high-speed train noise were assessed through laboratory experiments. A total of ten sites with varying landscape metrics were chosen for audio-visual recording. The acoustical characteristics of the high-speed train noise were analyzed using various noise level indices. Landscape metrics such as the percentage of natural features (NF) and Shannon's diversity index (SHDI) were adopted to evaluate the landscape features of the ten sites. Laboratory experiments were then performed with 20 well-trained listeners to investigate the perception of high-speed train noise in rural areas. The experiments consisted of three parts: 1) visual-only condition, 2) audio-only condition, and 3) combined audio-visual condition. The results showed that subjects' preference for visual images was significantly related to NF, the number of land types, and the A-weighted equivalent sound pressure level (LAeq). In addition, the visual images significantly influenced the noise annoyance, and LAeq and NF were the dominant factors affecting the annoyance from high-speed train noise in the combined audio-visual condition. In addition, Zwicker's loudness (N) was highly correlated with the annoyance from high-speed train noise in both the audio-only and audio-visual conditions. © 2013.

Welding arc and plasma studies using real time, multipass holographic interferometry

NASA Technical Reports Server (NTRS)

Deason, Vance

1987-01-01

Flow visualization of the plasma process in a welding arc is being studied with a multipass Argon ion interferometer. High speed movies at 10,000 frames per/sec are taken. The multipass interferometer and several interferograms of the plasma near the electrode of the welding are given. Digitization of the fringes is currently done by hand.

Flow Visualization Proposed for Vacuum Cleaner Nozzle Designs

NASA Technical Reports Server (NTRS)

2005-01-01

In 1995, the NASA Lewis Research Center and the Kirby Company (a major vacuum cleaner company) began negotiations for a Space Act Agreement to conduct research, technology development, and testing involving the flow behavior of airborne particulate flow behavior. Through these research efforts, we hope to identify ways to improve suction, flow rate, and surface agitation characteristics of nozzles used in vacuum cleaner nozzles. We plan to apply an advanced visualization technology, known as Stereoscopic Imaging Velocimetry (SIV), to a Kirby G-4 vacuum cleaner. Resultant data will be analyzed with a high-speed digital motion analysis system. We also plan to evaluate alternative vacuum cleaner nozzle designs. The overall goal of this project is to quantify both velocity fields and particle trajectories throughout the vacuum cleaner nozzle to optimize its "cleanability"--its ability to disturb and remove embedded dirt and other particulates from carpeting or hard surfaces. Reference

Unified Application of Vapor Screen Flow Visualization and Pressure Sensitive Paint Measurement Techniques to Vortex- and Shock Wave-Dominated Flow Fields

NASA Technical Reports Server (NTRS)

Erickson, Gary E.

2010-01-01

Laser vapor screen (LVS) flow visualization and pressure sensitive paint (PSP) techniques were applied in a unified approach to wind tunnel testing of slender wing and missile configurations dominated by vortex flows and shock waves at subsonic, transonic, and supersonic speeds. The off-surface cross-flow patterns using the LVS technique were combined with global PSP surface static pressure mappings to characterize the leading-edge vortices and shock waves that coexist and interact at high angles of attack. The synthesis of LVS and PSP techniques was also effective in identifying the significant effects of passive surface porosity and the presence of vertical tail surfaces on the flow topologies. An overview is given of LVS and PSP applications in selected experiments on small-scale models of generic slender wing and missile configurations in the NASA Langley Research Center (NASA LaRC) Unitary Plan Wind Tunnel (UPWT) and 8-Foot Transonic Pressure Tunnel (8-Foot TPT).

Unified Application Vapor Screen Flow Visualization and Pressure Sensitive Paint Measurement Techniques to Vortex- and Shock Wave-Dominated Flow Fields

NASA Technical Reports Server (NTRS)

Erickson, Gary E.

2008-01-01

Laser vapor screen (LVS) flow visualization and pressure sensitive paint (PSP) techniques were applied in a unified approach to wind tunnel testing of slender wing and missile configurations dominated by vortex flows and shock waves at subsonic, transonic, and supersonic speeds. The off-surface cross-flow patterns using the LVS technique were combined with global PSP surface static pressure mappings to characterize the leading-edge vortices and shock waves that coexist and interact at high angles of attack (alpha). The synthesis of LVS and PSP techniques was also effective in identifying the significant effects of passive surface porosity and the presence of vertical tail surfaces on the flow topologies. An overview is given of LVS and PSP applications in selected experiments on small-scale models of generic slender wing and missile configurations in the NASA Langley Research Center (NASA LaRC) Unitary Plan Wind Tunnel (UPWT) and 8-Foot Transonic Pressure Tunnel (8-Foot TPT).

Water Tunnel Flow Visualization Study Through Poststall of 12 Novel Planform Shapes

NASA Technical Reports Server (NTRS)

Gatlin, Gregory M.; Neuhart, Dan H.

1996-01-01

To determine the flow field characteristics of 12 planform geometries, a flow visualization investigation was conducted in the Langley 16- by 24-Inch Water Tunnel. Concepts studied included flat plate representations of diamond wings, twin bodies, double wings, cutout wing configurations, and serrated forebodies. The off-surface flow patterns were identified by injecting colored dyes from the model surface into the free-stream flow. These dyes generally were injected so that the localized vortical flow patterns were visualized. Photographs were obtained for angles of attack ranging from 10' to 50', and all investigations were conducted at a test section speed of 0.25 ft per sec. Results from the investigation indicate that the formation of strong vortices on highly swept forebodies can improve poststall lift characteristics; however, the asymmetric bursting of these vortices could produce substantial control problems. A wing cutout was found to significantly alter the position of the forebody vortex on the wing by shifting the vortex inboard. Serrated forebodies were found to effectively generate multiple vortices over the configuration. Vortices from 65' swept forebody serrations tended to roll together, while vortices from 40' swept serrations were more effective in generating additional lift caused by their more independent nature.

Application of support vector regression for optimization of vibration flow field of high-density polyethylene melts characterized by small angle light scattering

NASA Astrophysics Data System (ADS)

Xian, Guangming

2018-03-01

In this paper, the vibration flow field parameters of polymer melts in a visual slit die are optimized by using intelligent algorithm. Experimental small angle light scattering (SALS) patterns are shown to characterize the processing process. In order to capture the scattered light, a polarizer and an analyzer are placed before and after the polymer melts. The results reported in this study are obtained using high-density polyethylene (HDPE) with rotation speed at 28 rpm. In addition, support vector regression (SVR) analytical method is introduced for optimization the parameters of vibration flow field. This work establishes the general applicability of SVR for predicting the optimal parameters of vibration flow field.

Experimental study of microbubble drag reduction on an axisymmetric body

NASA Astrophysics Data System (ADS)

Song, Wuchao; Wang, Cong; Wei, Yingjie; Zhang, Xiaoshi; Wang, Wei

2018-01-01

Microbubble drag reduction on the axisymmetric body is experimentally investigated in the turbulent water tunnel. Microbubbles are created by injecting compressed air through the porous medium with various average pore sizes. The morphology of microbubble flow and the size distribution of microbubble are observed by the high-speed visualization system. Drag measurements are obtained by the balance which is presented as the function of void ratio. The results show that when the air injection flow rate is high, uniformly dispersed microbubble flow is coalesced into an air layer with the larger increment rate of drag reduction ratio. The diameter distributions of microbubble under various conditions are submitted to normal distribution. Microbubble drag reduction can be divided into three distinguishable regions in which the drag reduction ratio experiences increase stage, rapid increase stage and stability stage, respectively, corresponding to the various morphologies of microbubble flow. Moreover, drag reduction ratio increases with the decreasing pore sizes of porous medium at the identical void ratio in the area of low speeds, while the effect of pore sizes on drag reduction is reduced gradually until it disappears with the increasing free stream speeds, which indicates that smaller microbubbles have better efficiency in drag reduction. This research results help to improve the understanding of microbubble drag reduction and provides helpful references for practical applications.

Visualization of Biosurfactant Film Flow in a Bacillus subtilis Swarm Colony on an Agar Plate

PubMed Central

Kim, Kyunghoon; Kim, Jung Kyung

2015-01-01

Collective bacterial dynamics plays a crucial role in colony development. Although many research groups have studied the behavior of fluidic swarm colonies, the detailed mechanics of its motion remains elusive. Here, we developed a visualization method using submicron fluorescent beads for investigating the flow field in a thin layer of fluid that covers a Bacillus subtilis swarm colony growing on an agar plate. The beads were initially embedded in the agar plate and subsequently distributed spontaneously at the upper surface of the expanding colony. We conducted long-term live cell imaging of the B. subtilis colony using the fluorescent tracers, and obtained high-resolution velocity maps of microscale vortices in the swarm colony using particle image velocimetry. A distinct periodic fluctuation in the average speed and vorticity of flow in swarm colony was observed at the inner region of the colony, and correlated with the switch between bacterial swarming and growth phases. At the advancing edge of the colony, both the magnitudes of velocity and vorticity of flow in swarm colony were inversely correlated with the spreading speed of the swarm edge. The advanced imaging tool developed in this study would facilitate further understanding of the effect of micro vortices in swarm colony on the collective dynamics of bacteria. PMID:26343634

Visualization of Biosurfactant Film Flow in a Bacillus subtilis Swarm Colony on an Agar Plate.

PubMed

Kim, Kyunghoon; Kim, Jung Kyung

2015-08-26

Collective bacterial dynamics plays a crucial role in colony development. Although many research groups have studied the behavior of fluidic swarm colonies, the detailed mechanics of its motion remains elusive. Here, we developed a visualization method using submicron fluorescent beads for investigating the flow field in a thin layer of fluid that covers a Bacillus subtilis swarm colony growing on an agar plate. The beads were initially embedded in the agar plate and subsequently distributed spontaneously at the upper surface of the expanding colony. We conducted long-term live cell imaging of the B. subtilis colony using the fluorescent tracers, and obtained high-resolution velocity maps of microscale vortices in the swarm colony using particle image velocimetry. A distinct periodic fluctuation in the average speed and vorticity of flow in swarm colony was observed at the inner region of the colony, and correlated with the switch between bacterial swarming and growth phases. At the advancing edge of the colony, both the magnitudes of velocity and vorticity of flow in swarm colony were inversely correlated with the spreading speed of the swarm edge. The advanced imaging tool developed in this study would facilitate further understanding of the effect of micro vortices in swarm colony on the collective dynamics of bacteria.

Analysis of Dynamic Data from Supersonic Retropropulsion Experiments in NASA Langley's Unitary Plan Wind Tunnel

NASA Technical Reports Server (NTRS)

Codoni, Joshua R.; Berry, Scott A.

2012-01-01

Recent experimental supersonic retropropulsion tests were conducted at the NASA Langley Research Center Unitary Plan Wind Tunnel Test Section 2 for a range of Mach numbers from 2.4 to 4.6. A 5-inch 70-degree sphere-cone forebody model with a 10-inch cylindrical aftbody experimental model was used which is capable of multiple retrorocket configurations. These configurations include a single central nozzle on the center point of the forebody, three nozzles at the forebody half-radius, and a combination of the first two configurations with no jets being plugged. A series of measurements were achieved through various instrumentation including forebody and aftbody pressure, internal pressures and temperatures, and high speed Schlieren visualization. Specifically, several high speed pressure transducers on the forebody and in the plenum were implemented to look at unsteady flow effects. The following work focuses on analyzing frequency traits due to the unsteady flow for a range of thrust coefficients for single, tri, and quad-nozzle test cases at freestream Mach 4.6 and angle of attack ranging from -8 degrees to +20 degrees. This analysis uses Matlab s fast Fourier transform, Welch's method (modified average of a periodogram), to create a power spectral density and analyze any high speed pressure transducer frequency traits due to the unsteady flow.

Predation by the Dwarf Seahorse on Copepods: Quantifying Motion and Flows Using 3D High Speed Digital Holographic Cinematography - When Seahorses Attack!

NASA Astrophysics Data System (ADS)

Gemmell, Brad; Sheng, Jian; Buskey, Ed

2008-11-01

Copepods are an important planktonic food source for most of the world's fish species. This high predation pressure has led copepods to evolve an extremely effective escape response, with reaction times to hydrodynamic disturbances of less than 4 ms and escape speeds of over 500 body lengths per second. Using 3D high speed digital holographic cinematography (up to 2000 frames per second) we elucidate the role of entrainment flow fields generated by a natural visual predator, the dwarf seahorse (Hippocampus zosterae) during attacks on its prey, Acartia tonsa. Using phytoplankton as a tracer, we recorded and reconstructed 3D flow fields around the head of the seahorse and its prey during both successful and unsuccessful attacks to better understand how some attacks lead to capture with little or no detection from the copepod while others result in failed attacks. Attacks start with a slow approach to minimize the hydro-mechanical disturbance which is used by copepods to detect the approach of a potential predator. Successful attacks result in the seahorse using its pipette-like mouth to create suction faster than the copepod's response latency. As these characteristic scales of entrainment increase, a successful escape becomes more likely.

High quality optical microangiography of ocular microcirculation and measurement of total retinal blood flow in mouse eye

NASA Astrophysics Data System (ADS)

Zhi, Zhongwei; Yin, Xin; Dziennis, Suzan; Alpers, Charles E.; Wang, Ruikang K.

2013-03-01

Visualization and measurement of retinal blood flow (RBF) is important to the diagnosis and management of different eye diseases, including diabetic retinopathy. Optical microangiography (OMAG) is developed for generating 3D dynamic microcirculation image and later refined into ultra-high sensitive OMAG (UHS-OMAG) for true capillary vessels imaging. Here, we present the application of OMAG imaging technique for visualization of depth-resolved vascular network within retina and choroid as well as measurement of total retinal blood flow in mice. A fast speed spectral domain OCT imaging system at 820nm with a line scan rate of 140 kHz was developed to image mouse posterior eye. By applying UHS-OMAG scanning protocol and processing algorithm, we achieved true capillary level imaging of retina and choroid vasculature in mouse eye. The vascular pattern within different retinal layers and choroid was presented. An en face Doppler OCT approach [1] without knowing Doppler angle was adopted for the measurement of total retinal blood flow. The axial blood flow velocity is measured in an en face plane by raster scanning and the flow is calculated by integrating over the vessel area of the central retinal artery.

Kinematics and dynamics of vortex rings in a tube

NASA Technical Reports Server (NTRS)

Brasseur, J. G.

1979-01-01

Kinematic theory and flow visualization experiments were combined to examine the dynamic processes which control the evolution of vortex rings from very low to very high Reynolds numbers, and to assess the effects of the wall as a vortex ring travels up a tube. The kinematic relationships among the size, shape, speed, and strength of vortex rings in a tube were computed from the theory. Relatively simple flow visualization measurements were used to calculate the total circulation of a vortex rings at a given time. Using this method, the strength was computated and plotted as a function of time for experimentally produced vortex rings. Reynolds number relationships are established and quantitative differences among the three Reynolds number groups are discussed.

CFD Application to Flow-Accelerated Corrosion in Feeder Bends

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pietralik, John M.; Smith, Bruce A.W.

2006-07-01

Feeder piping in CANDU{sup R} plants experiences a thinning degradation mechanism called Flow-Accelerated Corrosion (FAC). The piping is made of carbon steel and has high water flow speeds. Although the water chemistry is highly alkaline with room-temperature pH in a range of 10.0-10.5, the piping has FAC rates exceeding 0.1 mm/year in some locations, e.g., in bends. One of the most important parameters affecting the FAC rate is the mass transfer coefficient for convective mass transport of ferrous ions. The ions are created at the pipe wall as a result of corrosion, diffuse through the oxide layer, and are transportedmore » from the oxide-layer/water interface to the bulk water by mass transport. Consequently, the local flow characteristics contribute to the highly turbulent convective mass transfer. Plant data and laboratory experiments indicate that the mass transfer step dominates FAC under feeder conditions. In this study, the flow and mass transfer in a feeder bend under operating conditions were simulated using the Fluent{sup TM} computer code. Because the flow speed is very high, with the Reynolds numbers in a range of several millions, and because the geometry is complex, experiments in a 1:1 scale were conducted with the main objective to validate flow simulations. The experiments measured pressure at several key locations and visualized the flow. The flow and mass transfer models were validated using available friction-factor and mass transfer correlations and literature experiments on mass transfer in a bend. The validation showed that the turbulence model that best predicts the experiments is the realizable k-{epsilon} model. Other two-equation turbulence models, as well as one-equation models and Reynolds stress models were tried. The near-wall treatment used the non-equilibrium wall functions. The wall functions were modified for surface roughness when necessary. A comparison of the local mass transfer coefficient with measured FAC rate in plant specimens shows very good agreement. Visualization experiments indicate secondary flows in the bends. No boundary layer separation was observed in experiments or in simulations. (authors)« less

Laser-Based Optical System for Reactive Radical Concentration Measurements in Plasmas and Flames

DTIC Science & Technology

2006-08-01

role of different plasma components in chain propagation support: (1) and (2) - corona plasma generators with high-voltage multiple needle electrodes ; (3...H20 2) and HCN. Measurements in Gliding Arc, Dielectric Barrier Discharge and Pulsed Corona Plasma systems and in flame and flow reactor systems are...discharges operating in air with iron electrodes - 260V.35 Using visual quantification from high speed camera arc images, the approximate thickness of

High-Speed Boundary-Layer Transition: Study of Stationary Crossflow Using Spectral Analysis

NASA Astrophysics Data System (ADS)

McGuire, Patrick Joseph

Crossflow instability is primary cause of boundary-layer transition on swept wings used in high-speed applications. Delaying the downstream location of transition would drastically reduce the viscous drag over the wing surface, and subsequently improves the overall aircraft efficiency. By studying the development of instability growth rates and how they interact with the surroundings, researchers can control the crossflow transition location. Experiments on the 35° swept-wing model were performed in the NASA Langley 20-Inch Supersonic Wind Tunnel with Mach 2.0 flow conditions and 20 μm tall discrete roughness elements (DRE) with varying spacing placed along the leading edge. Fluorene was used as the sublimating chemical in the surface flow visualization technique to observe the transition front and stationary crossflow vortex patterns in the laminar flow region. Spatial spectral decomposition was completed on high-resolution images of sublimating chemical runs using a newly developed image processing technique. Streamwise evolution of the vortex track wavelengths within the laminar boundary-layer region was observed. The spectral information was averaged to produce dominant modes present throughout the laminar region.

Wind tunnel investigations of forebody strakes for yaw control on F/A-18 model at subsonic and transonic speeds

NASA Technical Reports Server (NTRS)

Erickson, Gary E.; Murri, Daniel G.

1993-01-01

Wind tunnel investigations have been conducted of forebody strakes for yaw control on 0.06-scale models of the F/A-18 aircraft at free-stream Mach numbers of 0.20 to 0.90. The testing was conducted in the 7- by 10-Foot Transonic Tunnel at the David Taylor Research Center and the Langley 7- by 10-Foot High-Speed Tunnel. The principal objectives of the testing were to determine the effects of the Mach number and the strake plan form on the strake yaw control effectiveness and the corresponding strake vortex induced flow field. The wind tunnel model configurations simulated an actuated conformal strake deployed for maximum yaw control at high angles of attack. The test data included six-component forces and moments on the complete model, surface static pressure distributions on the forebody and wing leading-edge extensions, and on-surface and off-surface flow visualizations. The results from these studies show that the strake produces large yaw control increments at high angles of attack that exceed the effect of conventional rudders at low angles of attack. The strake yaw control increments diminish with increasing Mach number but continue to exceed the effect of rudder deflection at angles of attack greater than 30 degrees. The character of the strake vortex induced flow field is similar at subsonic and transonic speeds. Cropping the strake planform to account for geometric and structural constraints on the F-18 aircraft has a small effect on the yaw control increments at subsonic speeds and no effect at transonic speeds.

Wake visualization of a heaving and pitching foil in a soap film

NASA Astrophysics Data System (ADS)

Muijres, Florian T.; Lentink, David

2007-11-01

Many fish depend primarily on their tail beat for propulsion. Such a tail is commonly modeled as a two-dimensional flapping foil. Here we demonstrate a novel experimental setup of such a foil that heaves and pitches in a soap film. The vortical flow field generated by the foil correlates with thickness variations in the soap film, which appear as interference fringes when the film is illuminated with a monochromatic light source (we used a high-frequency SOX lamp). These interference fringes are subsequently captured with high-speed video (500 Hz) and this allows us to study the unsteady vortical field of a flapping foil. The main advantage of our approach is that the flow fields are time and space resolved and can be obtained time-efficiently. The foil is driven by a flapping mechanism that is optimized for studying both fish swimming and insect flight inside and outside the behavioral envelope. The mechanism generates sinusoidal heave and pitch kinematics, pre-described by the non-dimensional heave amplitude (0-6), the pitch amplitude (0°-90°), the phase difference between pitch and heave (0°-360°), and the dimensionless wavelength of the foil (3-18). We obtained this wide range of wavelengths for a foil 4 mm long by minimizing the soap film speed (0.25 m s-1) and maximizing the flapping frequency range (4-25 Hz). The Reynolds number of the foil is of order 1,000 throughout this range. The resulting setup enables an effective assessment of vortex wake topology as a function of flapping kinematics. The efficiency of the method is further improved by carefully eliminating background noise in the visualization (e.g., reflections of the mechanism). This is done by placing mirrors at an angle behind the translucent film such that the camera views the much more distant and out-of-focus reflections of the black laboratory wall. The resulting high-quality flow visualizations require minimal image processing for flow interpretation. Finally, we demonstrate the effectiveness of our setup by visualizing the vortex dynamics of the flapping foil as a function of pitch amplitude by assessing the symmetry of the vortical wake.

Wake visualization of a heaving and pitching foil in a soap film

NASA Astrophysics Data System (ADS)

Muijres, Florian T.; Lentink, David

Many fish depend primarily on their tail beat for propulsion. Such a tail is commonly modeled as a twodimensional flapping foil. Here we demonstrate a novel experimental setup of such a foil that heaves and pitches in a soap film. The vortical flow field generated by the foil correlates with thickness variations in the soap film, which appear as interference fringes when the film is illuminated with a monochromatic light source (we used a high-frequency SOX lamp). These interference fringes are subsequently captured with high-speed video (500 Hz) and this allows us to study the unsteady vortical field of a flapping foil. The main advantage of our approach is that the flow fields are time and space resolved and can be obtained time-efficiently. The foil is driven by a flapping mechanism that is optimized for studying both fish swimming and insect flight inside and outside the behavioral envelope. The mechanism generates sinusoidal heave and pitch kinematics, pre-described by the non-dimensional heave amplitude (0-6), the pitch amplitude (0° - 90°), the phase difference between pitch and heave (0° - 360°), and the dimensionless wavelength of the foil (3-18). We obtained this wide range of wavelengths for a foil 4 mm long by minimizing the soap film speed (0.25 m s- 1) and maximizing the flapping frequency range (4-25 Hz). The Reynolds number of the foil is of order 1,000 throughout this range. The resulting setup enables an effective assessment of vortex wake topology as a function of flapping kinematics. The efficiency of the method is further improved by carefully eliminating background noise in the visualization (e.g., reflections of the mechanism). This is done by placing mirrors at an angle behind the translucent film such that the camera views the much more distant and out-of-focus reflections of the black laboratory wall. The resulting high-quality flow visualizations require minimal image processing for flow interpretation. Finally, we demonstrate the effectiveness of our setup by visualizing the vortex dynamics of the flapping foil as a function of pitch amplitude by assessing the symmetry of the vortical wake.

Scientific Visualization in High Speed Network Environments

NASA Technical Reports Server (NTRS)

Vaziri, Arsi; Kutler, Paul (Technical Monitor)

1997-01-01

In several cases, new visualization techniques have vastly increased the researcher's ability to analyze and comprehend data. Similarly, the role of networks in providing an efficient supercomputing environment have become more critical and continue to grow at a faster rate than the increase in the processing capabilities of supercomputers. A close relationship between scientific visualization and high-speed networks in providing an important link to support efficient supercomputing is identified. The two technologies are driven by the increasing complexities and volume of supercomputer data. The interaction of scientific visualization and high-speed networks in a Computational Fluid Dynamics simulation/visualization environment are given. Current capabilities supported by high speed networks, supercomputers, and high-performance graphics workstations at the Numerical Aerodynamic Simulation Facility (NAS) at NASA Ames Research Center are described. Applied research in providing a supercomputer visualization environment to support future computational requirements are summarized.

Airflow and optic flow mediate antennal positioning in flying honeybees

PubMed Central

Roy Khurana, Taruni; Sane, Sanjay P

2016-01-01

To maintain their speeds during navigation, insects rely on feedback from their visual and mechanosensory modalities. Although optic flow plays an essential role in speed determination, it is less reliable under conditions of low light or sparse landmarks. Under such conditions, insects rely on feedback from antennal mechanosensors but it is not clear how these inputs combine to elicit flight-related antennal behaviours. We here show that antennal movements of the honeybee, Apis mellifera, are governed by combined visual and antennal mechanosensory inputs. Frontal airflow, as experienced during forward flight, causes antennae to actively move forward as a sigmoidal function of absolute airspeed values. However, corresponding front-to-back optic flow causes antennae to move backward, as a linear function of relative optic flow, opposite the airspeed response. When combined, these inputs maintain antennal position in a state of dynamic equilibrium. DOI: http://dx.doi.org/10.7554/eLife.14449.001 PMID:27097104

Noninvasive OCT imaging of the retinal morphology and microvasculature based on the combination of the phase and amplitude method

NASA Astrophysics Data System (ADS)

Qin, Lin; Fan, Shanhui; Zhou, Chuanqing

2017-04-01

To implement the optical coherence tomography (OCT) angiography on the low scanning speed OCT system, we developed a joint phase and amplitude method to generate 3-D angiograms by analysing the frequency distribution of signals from non-moving and moving scatterers and separating the signals from the tissue and blood flow with high-pass filter dynamically. This approach firstly compensates the sample motion between adjacent A-lines. Then according to the corrected phase information, we used a histogram method to determine the bulk non-moving tissue phases dynamically, which is regarded as the cut-off frequency of a high-pass filter, and separated the moving and non-moving scatters using the mentioned high-pass filter. The reconstructed image can visualize the components of moving scatters flowing, and enables volumetric flow mapping combined with the corrected phase information. Furthermore, retinal and choroidal blood vessels can be simultaneously obtained by separating the B-scan into retinal part and choroidal parts using a simple segmentation algorithm along the RPE. After the compensation of axial displacements between neighbouring images, three-dimensional vasculature of ocular vessels has been visualized. Experiments were performed to demonstrate the effectiveness of the proposed method for 3-D vasculature imaging of human retina and choroid. The results revealed depth-resolved vasculatures in retina and choroid, suggesting that our approach can be used for noninvasive and three-dimensional angiography with a low-speed clinical OCT, and it has a great potential for clinic application.

A vapor generator for transonic flow visualization

NASA Technical Reports Server (NTRS)

Bruce, Robert A.; Hess, Robert W.; Rivera, Jose A., Jr.

1989-01-01

A vapor generator was developed for use in the NASA Langley Transonic Dynamics Tunnel (TDT). Propylene glycol was used as the vapor material. The vapor generator system was evaluated in a laboratory setting and then used in the TDT as part of a laser light sheet flow visualization system. The vapor generator provided satisfactory seeding of the air flow with visible condensate particles, smoke, for tests ranging from low subsonic through transonic speeds for tunnel total pressures from atmospheric pressure down to less than 0.1 atmospheric pressure.

20 kHz toluene planar laser-induced fluorescence imaging of a jet in nearly sonic crossflow

NASA Astrophysics Data System (ADS)

Miller, V. A.; Troutman, V. A.; Mungal, M. G.; Hanson, R. K.

2014-10-01

This manuscript describes continuous, high-repetition-rate (20 kHz) toluene planar laser-induced fluorescence (PLIF) imaging in an expansion tube impulse flow facility. Cinematographic image sequences are acquired that visualize an underexpanded jet of hydrogen in Mach 0.9 crossflow, a practical flow configuration relevant to aerospace propulsion systems. The freestream gas is nitrogen seeded with toluene; toluene broadly absorbs and fluoresces in the ultraviolet, and the relatively high quantum yield of toluene produces large signals and high signal-to-noise ratios. Toluene is excited using a commercially available, frequency-quadrupled (266 nm), high-repetition-rate (20 kHz), pulsed (0.8-0.9 mJ per pulse), diode-pumped solid-state Nd:YAG laser, and fluorescence is imaged with a high-repetition-rate intensifier and CMOS camera. The resulting PLIF movie and image sequences are presented, visualizing the jet start-up process and the dynamics of the jet in crossflow; the freestream duration and a measure of freestream momentum flux steadiness are also inferred. This work demonstrates progress toward continuous PLIF imaging of practical flow systems in impulse facilities at kHz acquisition rates using practical, turn-key, high-speed laser and imaging systems.

Visualizing and Quantifying Blob Characteristics on NSTX

NASA Astrophysics Data System (ADS)

Davis, William; Zweben, Stewart; Myra, James; D'Ippolito, Daniel; Ko, Matthew

2012-10-01

Understanding the radial motion of blob-filaments in the tokamak edge plasma is important since this motion can affect the width of the heat and particle scrape-off layer (SOL) [1]. High resolution (64x80), high speed (400,000 frames/sec) edge turbulence movies taken of the NSTX outer midplane separatrix region have recently been analyzed for blob motion. Regions of high light emission from gas puff imaging within a 25x30 cm cross-section were used to track blob-filaments in the plasma edge and into the SOL. Software tools have been developed for visualizing blob movement and automatically generating statistics of blob speed, shape, amplitude, size, and orientation; thousands of blobs have been analyzed for dozens of shots. The blob tracking algorithm and resulting database entries are explained in detail. Visualization tools also show how poloidal and radial motion change as blobs move through the scrape-off-layer (SOL), e.g. suggesting the influence of sheared flow. Relationships between blob size and velocity are shown for various types of plasmas and compared with simplified theories of blob motion. This work was supported by DOE Contract DE-AC02-09-CH11466. [4pt] [1] J.R. Myra et al, Phys. Plasmas 18, 012305 (2011)

Study of compressible turbulent flows in supersonic environment by large-eddy simulation

NASA Astrophysics Data System (ADS)

Genin, Franklin

The numerical resolution of turbulent flows in high-speed environment is of fundamental importance but remains a very challenging problem. First, the capture of strong discontinuities, typical of high-speed flows, requires the use of shock-capturing schemes, which are not adapted to the resolution of turbulent structures due to their intrinsic dissipation. On the other hand, low-dissipation schemes are unable to resolve shock fronts and other sharp gradients without creating high amplitude numerical oscillations. Second, the nature of turbulence in high-speed flows differs from its incompressible behavior, and, in the context of Large-Eddy Simulation, the subgrid closure must be adapted to the modeling of compressibility effects and shock waves on turbulent flows. The developments described in this thesis are two-fold. First, a state of the art closure approach for LES is extended to model subgrid turbulence in compressible flows. The energy transfers due to compressible turbulence and the diffusion of turbulent kinetic energy by pressure fluctuations are assessed and integrated in the Localized Dynamic ksgs model. Second, a hybrid numerical scheme is developed for the resolution of the LES equations and of the model transport equation, which combines a central scheme for turbulent resolutions to a shock-capturing method. A smoothness parameter is defined and used to switch from the base smooth solver to the upwind scheme in regions of discontinuities. It is shown that the developed hybrid methodology permits a capture of shock/turbulence interactions in direct simulations that agrees well with other reference simulations, and that the LES methodology effectively reproduces the turbulence evolution and physical phenomena involved in the interaction. This numerical approach is then employed to study a problem of practical importance in high-speed mixing. The interaction of two shock waves with a high-speed turbulent shear layer as a mixing augmentation technique is considered. It is shown that the levels of turbulence are increased through the interaction, and that the mixing is significantly improved in this flow configuration. However, the region of increased mixing is found to be localized to a region close to the impact of the shocks, and that the statistical levels of turbulence relax to their undisturbed levels some short distance downstream of the interaction. The present developments are finally applied to a practical configuration relevant to scramjet injection. The normal injection of a sonic jet into a supersonic crossflow is considered numerically, and compared to the results of an experimental study. A fair agreement in the statistics of mean and fluctuating velocity fields is obtained. Furthermore, some of the instantaneous flow structures observed in experimental visualizations are identified in the present simulation. The dynamics of the interaction for the reference case, based on the experimental study, as well as for a case of higher freestream Mach number and a case of higher momentum ratio, are examined. The classical instantaneous vortical structures are identified, and their generation mechanisms, specific to supersonic flow, are highlighted. Furthermore, two vortical structures, recently revealed in low-speed jets in crossflow but never documented for high-speed flows, are identified during the flow evolution.

Hummingbirds generate bilateral vortex loops during hovering: evidence from flow visualization

NASA Astrophysics Data System (ADS)

Pournazeri, Sam; Segre, Paolo S.; Princevac, Marko; Altshuler, Douglas L.

2012-12-01

Visualization of the vortex wake of a flying animal provides understanding of how wingbeat kinematics are translated into the aerodynamic forces for powering and controlling flight. Two general vortex flow patterns have been proposed for the wake of hovering hummingbirds: (1) The two wings form a single, merged vortex ring during each wing stroke; and (2) the two wings form bilateral vortex loops during each wing stroke. The second pattern was proposed after a study with particle image velocimetry that demonstrated bilateral source flows in a horizontal measurement plane underneath hovering Anna's hummingbirds ( Calypte anna). Proof of this hypothesis requires a clear perspective of bilateral pairs of vortices. Here, we used high-speed image sequences (500 frames per second) of C. anna hover feeding within a white plume to visualize the vortex wake from multiple perspectives. The films revealed two key structural features: (1) Two distinct jets of downwards airflow are present under each wing; and (2) vortex loops around each jet are shed during each upstroke and downstroke. To aid in the interpretation of the flow visualization data, we analyzed high-speed kinematic data (1,000 frames per second) of wing tips and wing roots as C. anna hovered in normal air. These data were used to refine several simplified models of vortex topology. The observed flow patterns can be explained by either a single loop model with an hourglass shape or a bilateral model, with the latter being more likely. When hovering in normal air, hummingbirds used an average stroke amplitude of 153.6° (range 148.9°-164.4°) and a wingbeat frequency of 38.5 Hz (range 38.1-39.1 Hz). When hovering in the white plume, hummingbirds used shallower stroke amplitudes ( bar{x} = 129.8°, range 116.3°-154.1°) and faster wingbeat frequencies ( bar{x} = 41.1 Hz, range 38.5-44.7 Hz), although the bilateral jets and associated vortices were observed across the full kinematic range. The plume did not significantly alter the air density or constrain the sustained muscle contractile frequency. Instead, higher wingbeat frequencies likely incurred a higher metabolic cost with the possible benefit of allowing the birds to more rapidly escape from the visually disruptive plume.

Hummingbirds generate bilateral vortex loops during hovering: evidence from flow visualization

NASA Astrophysics Data System (ADS)

Pournazeri, Sam; Segre, Paolo S.; Princevac, Marko; Altshuler, Douglas L.

2013-01-01

Visualization of the vortex wake of a flying animal provides understanding of how wingbeat kinematics are translated into the aerodynamic forces for powering and controlling flight. Two general vortex flow patterns have been proposed for the wake of hovering hummingbirds: (1) The two wings form a single, merged vortex ring during each wing stroke; and (2) the two wings form bilateral vortex loops during each wing stroke. The second pattern was proposed after a study with particle image velocimetry that demonstrated bilateral source flows in a horizontal measurement plane underneath hovering Anna's hummingbirds ( Calypte anna). Proof of this hypothesis requires a clear perspective of bilateral pairs of vortices. Here, we used high-speed image sequences (500 frames per second) of C. anna hover feeding within a white plume to visualize the vortex wake from multiple perspectives. The films revealed two key structural features: (1) Two distinct jets of downwards airflow are present under each wing; and (2) vortex loops around each jet are shed during each upstroke and downstroke. To aid in the interpretation of the flow visualization data, we analyzed high-speed kinematic data (1,000 frames per second) of wing tips and wing roots as C. anna hovered in normal air. These data were used to refine several simplified models of vortex topology. The observed flow patterns can be explained by either a single loop model with an hourglass shape or a bilateral model, with the latter being more likely. When hovering in normal air, hummingbirds used an average stroke amplitude of 153.6° (range 148.9°-164.4°) and a wingbeat frequency of 38.5 Hz (range 38.1-39.1 Hz). When hovering in the white plume, hummingbirds used shallower stroke amplitudes ( bar{x} = 129.8°, range 116.3°-154.1°) and faster wingbeat frequencies ( bar{x} = 41.1 Hz, range 38.5-44.7 Hz), although the bilateral jets and associated vortices were observed across the full kinematic range. The plume did not significantly alter the air density or constrain the sustained muscle contractile frequency. Instead, higher wingbeat frequencies likely incurred a higher metabolic cost with the possible benefit of allowing the birds to more rapidly escape from the visually disruptive plume.

Real-time image processing for particle tracking velocimetry

NASA Astrophysics Data System (ADS)

Kreizer, Mark; Ratner, David; Liberzon, Alex

2010-01-01

We present a novel high-speed particle tracking velocimetry (PTV) experimental system. Its novelty is due to the FPGA-based, real-time image processing "on camera". Instead of an image, the camera transfers to the computer using a network card, only the relevant information of the identified flow tracers. Therefore, the system is ideal for the remote particle tracking systems in research and industrial applications, while the camera can be controlled and data can be transferred over any high-bandwidth network. We present the hardware and the open source software aspects of the PTV experiments. The tracking results of the new experimental system has been compared to the flow visualization and particle image velocimetry measurements. The canonical flow in the central cross section of a a cubic cavity (1:1:1 aspect ratio) in our lid-driven cavity apparatus is used for validation purposes. The downstream secondary eddy (DSE) is the sensitive portion of this flow and its size was measured with increasing Reynolds number (via increasing belt velocity). The size of DSE estimated from the flow visualization, PIV and compressed PTV is shown to agree within the experimental uncertainty of the methods applied.

Fundamental Structure of High-Speed Reacting Flows: Supersonic Combustion and Detonation

DTIC Science & Technology

2016-04-30

AFRL-AFOSR-VA-TR-2016-0195 Fundamental Structure of High-Speed Reacting Flows: Supersonic Combustion and Detonation Kenneth Yu MARYLAND UNIV COLLEGE...MARCH 2016 4. TITLE AND SUBTITLE FUNDAMENTAL STRUCTURE OF HIGH-SPEED REACTING FLOWS: SUPERSONIC COMBUSTION AND DETONATION 5a. CONTRACT NUMBER...public release. Final Report on Fundamental Structure of High-Speed Reacting Flows: Supersonic Combustion and Detonation Grant

The art and science of flow control - case studies using flow visualization methods

NASA Astrophysics Data System (ADS)

Alvi, F. S.; Cattafesta, L. N., III

2010-04-01

Active flow control (AFC) has been the focus of significant research in the last decade. This is mainly due to the potentially substantial benefits it affords. AFC applications range from the subsonic to the supersonic (and beyond) regime for both internal and external flows. These applications are wide and varied, such as controlling flow transition and separation over various external components of the aircraft to active management of separation and flow distortion in engine components and over turbine and compressor blades. High-speed AFC applications include control of flow oscillations in cavity flows, supersonic jet screech, impinging jets, and jet-noise control. In this paper we review some of our recent applications of AFC through a number of case studies that illustrate the typical benefits as well as limitations of present AFC methods. The case studies include subsonic and supersonic canonical flowfields such as separation control over airfoils, control of supersonic cavity flows and impinging jets. In addition, properties of zero-net mass-flux (ZNMF) actuators are also discussed as they represent one of the most widely studied actuators used for AFC. In keeping with the theme of this special issue, the flowfield properties and their response to actuation are examined through the use of various qualitative and quantitative flow visualization methods, such as smoke, shadowgraph, schlieren, planar-laser scattering, and Particle image velocimetry (PIV). The results presented here clearly illustrate the merits of using flow visualization to gain significant insight into the flow and its response to AFC.

The Aeroacoustics and Aerodynamics of High-Speed Coanda Devices, Part 2: Effects of Modifications for Flow Control and Noise Reduction

NASA Astrophysics Data System (ADS)

Carpenter, P. W.; Smith, C.

1997-12-01

The paper describes two studies of the effects of flow control devices on the aerodynamics and aeroacoustics of a high-speed Coanda flow that is formed when a supersonic jet issues from a radial nozzle and adheres to a tulip-shaped body of revolution. Shadowgraphy and other flow-visualization techniques are used to reveal the various features of the complex flow fields. The acoustic characteristics are obtained from far- and near-field measurements with an array of microphones in an anechoic chamber. First the effects of incorporating a step between the annular exit slot and the Coanda surface are investigated. The step is incorporated to ensure that the breakaway pressure is raised to a level well above the maximum operating pressure. It substantially increases the complexity of the flow field and acoustic characteristics. In particular, it promotes the generation of two groups of discrete tones. A theoretical model based on a self-generated feedback loop is proposed to explain how these tones are generated. The second study investigates the effects of replacing the annular exit slot with a saw-toothed one with the aim of eliminating the discrete tones and thereby substantially reducing the level of noise generated.

Visualization of the Flow at the Tip of a High Speed Axial Flow Turbine Rotor Blade - An Assessment of Flow Visualisation Techniques and the Requirement of the Experimental Turbine.

DTIC Science & Technology

1987-11-01

71 AD-AI89 929 UI4A ~l HOFTEFOJA N TIPO IO PE /L S LO TUIN~. TCHN ?IRAEL’ITF 4XHH F IDNE AL. T U 87 AFOs -8-U N uNCLASSIFIED NIF-: Hrp li1.0 a18...Pulse tracer injection 16. 9) Detector sensor 17- 10) Focussed photomultiplier 17 Conceptual philosophy for the experimental turbine 18 Preliminary...tracing 35 2) Pulsed fluorescence 35 3) Single spot laser sensor 36 4) Two spot laser 36 5) Localised smoke pockets 37 6) Laser pulse smoke generation

An experimental investigation of hydrodynamic cavitation in micro-Venturis

NASA Astrophysics Data System (ADS)

Mishra, Chandan; Peles, Yoav

2006-10-01

The existence of hydrodynamic cavitation in the flow of de-ionized water through micro-Venturis has been witnessed in the form of traveling bubble cavitation and fully developed streamer bubble/supercavitation, and their mechanisms have been discussed. High-speed photography and flow visualization disclose inchoate cavitation bubbles emerging downstream from the micro-Venturi throat and the presence of a single streamer bubble/supercavity, which is equidistant from the micro device walls. The supercavity initiates inside the diffuser section and extends until the microchannel exit and proceeds to bifurcate the incoming flow. This article strives to provide numerical data and experimental details of hydrodynamic cavitation taking place within micro-Venturis.

A Resonant Pulse Detonation Actuator for High-Speed Boundary Layer Separation Control

NASA Technical Reports Server (NTRS)

Beck, B. T.; Cutler, A. D.; Drummond, J. P.; Jones, S. B.

2004-01-01

A variety of different types of actuators have been previously investigated as flow control devices. Potential applications include the control of boundary layer separation in external flows, as well as jet engine inlet and diffuser flow control. The operating principles for such devices are typically based on either mechanical deflection of control surfaces (which include MEMS flap devices), mass injection (which includes combustion driven jet actuators), or through the use of synthetic jets (diaphragm devices which produce a pulsating jet with no net mass flow). This paper introduces some of the initial flow visualization work related to the development of a relatively new type of combustion-driven jet actuator that has been proposed based on a pulse detonation principle. The device is designed to utilize localized detonation of a premixed fuel (Hydrogen)-air mixture to periodically inject a jet of gas transversely into the primary flow. Initial testing with airflow successfully demonstrated resonant conditions within the range of acoustic frequencies expected for the design. Schlieren visualization of the pulsating air jet structure revealed axially symmetric vortex flow, along with the formation of shocks. Flow visualization of the first successful sustained oscillation condition is also demonstrated for one configuration of the current test section. Future testing will explore in more detail the onset of resonant combustion and the approach to conditions of sustained resonant detonation.

Focused Schlieren flow visualization studies of multiple venturi fuel injectors in a high pressure combustor

NASA Technical Reports Server (NTRS)

Chun, K. S.; Locke, R. J.; Lee, C. M.; Ratvasky, W. J.

1994-01-01

Multiple venturi fuel injectors were used to obtain uniform fuel distributions, better atomization and vaporization in the premixing/prevaporizing section of a lean premixed/prevaporized flame tube combustor. A focused Schlieren system was used to investigate the fuel/air mixing effectiveness of various fuel injection configurations. The Schlieren system was focused to a plane within the flow field of a test section equipped with optical windows. The focused image plane was parallel to the axial direction of the flow and normal to the optical axis. Images from that focused plane, formed by refracted light due to density gradients within the flow field, were filmed with a high-speed movie camera at framing rates of 8,000 frames per second (fps). Three fuel injection concepts were investigated by taking high-speed movies of the mixture flows at various operating conditions. The inlet air temperature was varied from 600 F to 1000 F, and inlet pressures from 80 psia to 150 psia. Jet-A fuel was used typically at an equivalence ratio of 0.5. The intensity variations of the digitized Schlieren images were analytically correlated to spatial density gradients of the mixture flows. Qualitative measurements for degree of mixedness, intensity of mixing, and mixing completion time are shown. Various mixing performance patterns are presented with different configurations of fuel injection points and operating conditions.

A new method for laminar boundary layer transition visualization in flight: Color changes in liquid crystal coatings

NASA Technical Reports Server (NTRS)

Holmes, B. J.; Gall, P. D.; Croom, C. C.; Manuel, G. S.; Kelliher, W. C.

1986-01-01

The visualization of laminar to turbulent boundary layer transition plays an important role in flight and wind-tunnel aerodynamic testing of aircraft wing and body surfaces. Visualization can help provide a more complete understanding of both transition location as well as transition modes; without visualization, the transition process can be very difficult to understand. In the past, the most valuable transition visualization methods for flight applications included sublimating chemicals and oil flows. Each method has advantages and limitations. In particular, sublimating chemicals are impractical to use in subsonic applications much above 20,000 feet because of the greatly reduced rates of sublimation at lower temperatures (less than -4 degrees Farenheit). Both oil flow and sublimating chemicals have the disadvantage of providing only one good data point per flight. Thus, for many important flight conditions, transition visualization has not been readily available. This paper discusses a new method for visualizing transition in flight by the use of liquid crystals. The new method overcomes the limitations of past techniques, and provides transition visualization capability throughout almost the entire altitude and speed ranges of virtually all subsonic aircraft flight envelopes. The method also has wide applicability for supersonic transition visualization in flight and for general use in wind tunnel research over wide subsonic and supersonic speed ranges.

Visualization of irrigant flow and cavitation induced by Er:YAG laser within a root canal model.

PubMed

Matsumoto, Himeka; Yoshimine, Yoshito; Akamine, Akifumi

2011-06-01

Laser-activated irrigation (LAI) has recently been introduced as an innovative method for root canal irrigation. However, there is limited information about the cleaning mechanism of an Er:YAG laser. In this study, we visualized the action of laser-induced bubbles and fluid flow in vitro to better understand the physical mechanisms underlying LAI. An Er:YAG laser was equipped with a novel cone-shaped tip with a lateral emission rate of approximately 80%. Laser light was emitted at a pulse energy of 30, 50, or 70 mJ (output energy: 11, 18, or 26 mJ) and a repetition rate of 1 or 20 pulses per second, without air or water spray. Fluid flow dynamics in a root canal model were observed by using glass-bead tracers under a high-speed camera. Moreover, laser-induced bubble patterns were visualized in both free water and the root canal model. Tracers revealed high-speed motion of the fluid. A full cycle of expansion and implosion of vapor and secondary cavitation bubbles were clearly observed. In free water, the vapor bubble expanded for 220 microseconds, and its shape resembled that of an apple. In the root canal model, the vapor bubble expanded in a vertical direction along the canal wall, and bubble expansion continued for ≥700 microseconds. Furthermore, cavitation bubbles were created much more frequently in the canal model than in free water. These results suggest that the cleaning mechanism of an Er:YAG laser within the root canal might depend on rapid fluid motion caused by expansion and implosion of laser-induced bubbles. Copyright © 2011 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

A synchronous strobed laser light sheet for helicopter model rotor flow visualization

NASA Technical Reports Server (NTRS)

Leighty, Bradley D.; Rhodes, David B.; Jones, Stephen B.; Franke, John M.

1990-01-01

A synchronous, strobed laser light sheet has been developed for use in flow visualization of a helicopter rotor model. The light sheet strobe circuit included selectable blade position, strobe duration, and multiple pulses per revolution for rotors having 2 to 9 blades. The flow was seeded with propylene glycol. Between runs, a calibration grid board was placed in the plane of the laser sheet and recorded with the video camera at the position used to record the flow field. A slip-sync mode permitted slow motion visualization of the flow field over complete rotations of the rotor. The system was used to make two-dimensional flow field cuts of a four-bladed rotor operating at advance ratio of 0.37 at wind tunnel speeds up to 79.25 meters per second (260 feet per second).

Hot gas ingestion test results of a two-poster vectored thrust concept with flow visualization in the NASA Lewis 9- by 15-foot low speed wind tunnel

NASA Technical Reports Server (NTRS)

Johns, Albert L.; Neiner, George; Bencic, Timothy J.; Flood, Joseph D.; Amuedo, Kurt C.

1990-01-01

A 9.2 percent scale STOVL hot gas ingestion model was tested in the NASA Lewis 9 x 15-foot Low-Speed Wind Tunnel. Flow visualization from the Phase 1 test program, which evaluated the hot ingestion phenomena and control techniques, is covered. The Phase 2 test program evaluated the hot gas ingestion phenomena at higher temperatures and used a laser sheet to investigate the flow field. Hot gas ingestion levels were measured for the several forward nozzle splay configurations and with flow control/life improvement devices (LIDs) which reduced the hot gas ingestion. The test was conducted at full scale nozzle pressure ratios and inlet Mach numbers. Results are presented over a range of nozzle pressure ratios at a 10 kn headwind velocity. The Phase 2 program was conducted at exhaust nozzle temperatures up to 1460 R and utilized a sheet laser system for flow visualization of the model flow field in and out of ground effects. The results reported are for nozzle exhaust temperatures up to 1160 R and contain the compressor face pressure and temperature distortions, the total pressure recovery, the inlet temperature rise, and the environmental effects of the hot gas. The environmental effects include the ground plane contours, the model airframe heating, and the location of the ground flow separation.

Visualization of Flow Separation Around an Atmospheric Entry Capsule at Low-Subsonic Mach Number Using Background-Oriented Schlieren (BOS)

NASA Technical Reports Server (NTRS)

Mizukaki, Toshiharu; Borg, Stephen E.; Danehy, Paul M.; Murman, Scott M.

2014-01-01

This paper presents the results of visualization of separated flow around a generic entry capsule that resembles the Apollo Command Module (CM) and the Orion Multi-Purpose Crew Vehicle (MPCV). The model was tested at flow speeds up to Mach 0.4 at a single angle of attack of 28 degrees. For manned spacecraft using capsule-shaped vehicles, certain flight operations such as emergency abort maneuvers soon after launch and flight just prior to parachute deployment during the final stages of entry, the command module may fly at low Mach number. Under these flow conditions, the separated flow generated from the heat-shield surface on both windward and leeward sides of the capsule dominates the wake flow downstream of the capsule. In this paper, flow visualization of the separated flow was conducted using the background-oriented schlieren (BOS) method, which has the capability of visualizing significantly separated wake flows without the particle seeding required by other techniques. Experimental results herein show that BOS has detection capability of density changes on the order of 10(sup-5).

Design of a High-Reynolds Number Recirculating Water Tunnel

NASA Astrophysics Data System (ADS)

Daniel, Libin; Elbing, Brian

2014-11-01

An experimental fluid mechanics laboratory focused on turbulent boundary layers, drag reduction techniques, multiphase flows and fluid-structure interactions has recently been established at Oklahoma State University. This laboratory has three primary components; (1) a recirculating water tunnel, (2) a multiphase pipe flow loop, and (3) a multi-scale flow visualization system. The design of the water tunnel is the focus of this talk. The criteria used for the water tunnel design was that it had to produce a momentum-thickness based Reynolds number in excess of 104, negligible flow acceleration due to boundary layer growth, maximize optical access for use of the flow visualization system, and minimize inlet flow non-uniformity. This Reynolds number was targeted to bridge the gap between typical university/commercial water tunnels (103) and the world's largest water tunnel facilities (105) . These objectives were achieved with a 152 mm (6-inch) square test section that is 1 m long and has a maximum flow speed of 10 m/s. The flow non-uniformity was mitigated with the use of a tandem honeycomb configuration, a settling chamber and an 8.5:1 contraction. The design process that produced this final design will be presented along with its current status.

Advances in the Visualization and Analysis of Boundary Layer Flow in Swimming Fish

DTIC Science & Technology

2005-02-01

caudal-fin amputation on the kinematics and metabolic rate of underyearling sockeye salmon ( Oncorhynchus nerka ) at steady swimming speeds. J. Exp. Biol...caudal-fin amputation on the kinematics and metabolic rate of underyearling sockeye salmon ( Oncorhynchus nerka ) at steady swimming speeds. J. Exp. Biol

Speed Biases With Real-Life Video Clips

PubMed Central

Rossi, Federica; Montanaro, Elisa; de’Sperati, Claudio

2018-01-01

We live almost literally immersed in an artificial visual world, especially motion pictures. In this exploratory study, we asked whether the best speed for reproducing a video is its original, shooting speed. By using adjustment and double staircase methods, we examined speed biases in viewing real-life video clips in three experiments, and assessed their robustness by manipulating visual and auditory factors. With the tested stimuli (short clips of human motion, mixed human-physical motion, physical motion and ego-motion), speed underestimation was the rule rather than the exception, although it depended largely on clip content, ranging on average from 2% (ego-motion) to 32% (physical motion). Manipulating display size or adding arbitrary soundtracks did not modify these speed biases. Estimated speed was not correlated with estimated duration of these same video clips. These results indicate that the sense of speed for real-life video clips can be systematically biased, independently of the impression of elapsed time. Measuring subjective visual tempo may integrate traditional methods that assess time perception: speed biases may be exploited to develop a simple, objective test of reality flow, to be used for example in clinical and developmental contexts. From the perspective of video media, measuring speed biases may help to optimize video reproduction speed and validate “natural” video compression techniques based on sub-threshold temporal squeezing. PMID:29615875

Speed Biases With Real-Life Video Clips.

PubMed

Rossi, Federica; Montanaro, Elisa; de'Sperati, Claudio

2018-01-01

We live almost literally immersed in an artificial visual world, especially motion pictures. In this exploratory study, we asked whether the best speed for reproducing a video is its original, shooting speed. By using adjustment and double staircase methods, we examined speed biases in viewing real-life video clips in three experiments, and assessed their robustness by manipulating visual and auditory factors. With the tested stimuli (short clips of human motion, mixed human-physical motion, physical motion and ego-motion), speed underestimation was the rule rather than the exception, although it depended largely on clip content, ranging on average from 2% (ego-motion) to 32% (physical motion). Manipulating display size or adding arbitrary soundtracks did not modify these speed biases. Estimated speed was not correlated with estimated duration of these same video clips. These results indicate that the sense of speed for real-life video clips can be systematically biased, independently of the impression of elapsed time. Measuring subjective visual tempo may integrate traditional methods that assess time perception: speed biases may be exploited to develop a simple, objective test of reality flow, to be used for example in clinical and developmental contexts. From the perspective of video media, measuring speed biases may help to optimize video reproduction speed and validate "natural" video compression techniques based on sub-threshold temporal squeezing.

Cavitation on a scaled-down model of a Francis turbine guide vane: high-speed imaging and PIV measurements

NASA Astrophysics Data System (ADS)

Pervunin, K. S.; Timoshevskiy, M. V.; Churkin, S. A.; Kravtsova, A. Yu; Markovich, D. M.; Hanjalić, K.

2015-12-01

Cavitation on two symmetric foils, a NACA0015 hydrofoil and a scaled-down model of a Francis turbine guide vane (GV), was investigated by high-speed visualization and PIV. At small attack angles the differences between the profiles of the mean and fluctuating velocities for both hydrofoils were shown to be insignificant. However, at the higher angle of incidence, flow separation from the GV surface was discovered for quasi-steady regimes including cavitation-free and cavitation inception cases. The flow separation leads to the appearance of a second maximum in velocity fluctuations distributions downstream far from the GV surface. When the transition to unsteady regimes occurred, the velocity distributions became quite similar for both foils. Additionally, for the GV an unsteady regime characterized by asymmetric spanwise variations of the sheet cavity length along with alternating periodic detachments of clouds between the sidewalls of the test channel was for the first time visualized. This asymmetric behaviour is very likely to be governed by the cross instability that was recently described by Decaix and Goncalvès [8]. Moreover, it was concluded that the existence of the cross instability is independent on the test body shape and its aspect ratio.

Dual processing of visual rotation for bipedal stance control.

PubMed

Day, Brian L; Muller, Timothy; Offord, Joanna; Di Giulio, Irene

2016-10-01

When standing, the gain of the body-movement response to a sinusoidally moving visual scene has been shown to get smaller with faster stimuli, possibly through changes in the apportioning of visual flow to self-motion or environment motion. We investigated whether visual-flow speed similarly influences the postural response to a discrete, unidirectional rotation of the visual scene in the frontal plane. Contrary to expectation, the evoked postural response consisted of two sequential components with opposite relationships to visual motion speed. With faster visual rotation the early component became smaller, not through a change in gain but by changes in its temporal structure, while the later component grew larger. We propose that the early component arises from the balance control system minimising apparent self-motion, while the later component stems from the postural system realigning the body with gravity. The source of visual motion is inherently ambiguous such that movement of objects in the environment can evoke self-motion illusions and postural adjustments. Theoretically, the brain can mitigate this problem by combining visual signals with other types of information. A Bayesian model that achieves this was previously proposed and predicts a decreasing gain of postural response with increasing visual motion speed. Here we test this prediction for discrete, unidirectional, full-field visual rotations in the frontal plane of standing subjects. The speed (0.75-48 deg s(-1) ) and direction of visual rotation was pseudo-randomly varied and mediolateral responses were measured from displacements of the trunk and horizontal ground reaction forces. The behaviour evoked by this visual rotation was more complex than has hitherto been reported, consisting broadly of two consecutive components with respective latencies of ∼190 ms and >0.7 s. Both components were sensitive to visual rotation speed, but with diametrically opposite relationships. Thus, the early component decreased with faster visual rotation, while the later component increased. Furthermore, the decrease in size of the early component was not achieved by a simple attenuation of gain, but by a change in its temporal structure. We conclude that the two components represent expressions of different motor functions, both pertinent to the control of bipedal stance. We propose that the early response stems from the balance control system attempting to minimise unintended body motion, while the later response arises from the postural control system attempting to align the body with gravity. © 2016 The Authors. The Journal of Physiology published by John Wiley & Sons Ltd on behalf of The Physiological Society.

The effects of flow on schooling Devario aequipinnatus: school structure, startle response and information transmission

PubMed Central

Chicoli, A.; Butail, S.; Lun, Y.; Bak-Coleman, J.; Coombs, S.; Paley, D.A.

2014-01-01

To assess how flow affects school structure and threat detection, startle response rates of solitary and small groups of giant danio Devario aequipinnatus were compared to visual looming stimuli in flow and no-flow conditions. The instantaneous position and heading of each D. aequipinnatus were extracted from high-speed videos. Behavioural results indicate that (1) school structure is altered in flow such that D. aequipinnatus orient upstream while spanning out in a crosswise direction, (2) the probability of at least one D. aequipinnatus detecting the visual looming stimulus is higher in flow than no flow for both solitary D. aequipinnatus and groups of eight D. aequipinnatus, however, (3) the probability of three or more individuals responding is higher in no flow than flow. Taken together, these results indicate a higher probability of stimulus detection in flow but a higher probability of internal transmission of information in no flow. Finally, results were well predicted by a computational model of collective fright response that included the probability of direct detection (based on signal detection theory) and indirect detection (i.e. via interactions between group members) of threatening stimuli. This model provides a new theoretical framework for analysing the collective transfer of information among groups of fishes and other organisms. PMID:24773538

Visualisation of the flow at the tip of a high speed axial flow turbine rotor: An assessment of flow visualisation techniques and the requirement of the experimental turbine

NASA Astrophysics Data System (ADS)

Bindon, J.; Alder, D.; Ianovici, I.

1987-11-01

The field of flow visualization has been reviewed and its application to the study of the flow near the tip of an unshrouded axial turbine rotor discussed in detail. The logical conceptualization of experiments which could lead to a final understanding of the flow structure was developed and how this leads to test turbine design philosophy is suggested. The rotor periodicity shed by the stator requires that particle of pulse tracing is needed rather than the more universal continuous streamline trace which arises from a continuous tracer injection at a point in a flow. While the whole field of flow visualization at a rotor tip is demanding because of its very nature, pulse tracking will place a greater demand on the development of new skills and techniques. Since streamline tracking is somewhat more standard, these demands will not be as great. A fundamental choice does however need to be made between the two methods. The suggested experimental turbine should thus, always with the facility of infinitely variable Mach number, model the following: (1) Stationary annular cascade with tip clearance inside a stationary outer endwall; (2) Stationary annular cascade with tip clearance inside a moving endwall; (3) The transfer of flow visualization techniques developed into the rotating frame; (4) Fully rotating rotor with no inlet periodicity; (5) Fully rotating rotor with inlet periodicity.

A similitude method and the corresponding blade design of a low-speed large-scale axial compressor rotor

NASA Astrophysics Data System (ADS)

Yu, Chenghai; Ma, Ning; Wang, Kai; Du, Juan; Van den Braembussche, R. A.; Lin, Feng

2014-04-01

A similitude method to model the tip clearance flow in a high-speed compressor with a low-speed model is presented in this paper. The first step of this method is the derivation of similarity criteria for tip clearance flow, on the basis of an inviscid model of tip clearance flow. The aerodynamic parameters needed for the model design are then obtained from a numerical simulation of the target high-speed compressor rotor. According to the aerodynamic and geometric parameters of the target compressor rotor, a large-scale low-speed rotor blade is designed with an inverse blade design program. In order to validate the similitude method, the features of tip clearance flow in the low-speed model compressor are compared with the ones in the high-speed compressor at both design and small flow rate points. It is found that not only the trajectory of the tip leakage vortex but also the interface between the tip leakage flow and the incoming main flow in the high-speed compressor match well with that of its low speed model. These results validate the effectiveness of the similitude method for the tip clearance flow proposed in this paper.

Single-shot lifetime-based PSP and TSP measurements on turbocharger compressor blades

NASA Astrophysics Data System (ADS)

Peng, Di; Jiao, Lingrui; Yu, Yuelong; Liu, Yingzheng; Oshio, Tetsuya; Kawakubo, Tomoki; Yakushiji, Akimitsu

2017-09-01

Fast-responding pressure-sensitive paint (Fast PSP) and temperature-sensitive paint (TSP) measurements were conducted on two turbocharger compressors using a single-shot lifetime-based technique. The fast PSP and TSP were applied on separate blades of one compressor, and both paints were excited by a pulsed 532 nm Nd:YAG laser. The luminescent decay signals following the laser pulse were recorded by a CCD camera in a double-exposure mode. Instantaneous pressure and temperature fields on compressor blades were obtained simultaneously, for rotation speeds up to 150,000 rpm. The variations in pressure and temperature fields with rotation speed, flow rate and runtime were clearly visualized, showing the advantage of high spatial resolution. Severe image blurring problems and significant temperature-induced errors in the PSP results were found at high rotation speeds. The first issue was addressed by incorporating a deconvolution-based deblurring algorithm to recover the clear image from the blurred image using the combination of luminescent lifetime and rotation speed. The second issue was resolved by applying a pixel-by-pixel temperature correction based on the TSP results. The current technique has shown great capabilities in flow diagnostics of turbomachinery and can serve as a powerful tool for CFD validations and design optimizations.

Plastification of polymers in twin-screw-extruders: New visualization technic using high-speed imaging

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knieper, A., E-mail: Alexander.Knieper@lbf.fraunhofer.de, E-mail: Christian.Beinert@lbf.fraunhofer.de; Beinert, C., E-mail: Alexander.Knieper@lbf.fraunhofer.de, E-mail: Christian.Beinert@lbf.fraunhofer.de

The initial melting of the first granules through plastic energy dissipation (PED) at the beginning of the melting zone, in the co-rotating twin-screw extruder is visualized in this work. The visualization was created through the use of a high speed camera in the cross section of the melting zone. The parameters screw speed, granule-temperature, temperature-profile, type of polymer and back pressure were examined. It was shown that the screw speed and the temperature-profile have significant influence on the rate of initial melting.

Lee-side flow over delta wings at supersonic speeds

NASA Technical Reports Server (NTRS)

Miller, D. S.; Wood, R. M.

1985-01-01

An experimental investigation of the lee-side flow on sharp leading-edge delta wings at supersonic speeds has been conducted. Pressure data were obtained at Mach numbers from 1.5 to 2.8, and three types of flow-visualization data (oil-flow, tuft, and vapor-screen) were obtained at Mach numbers from 1.7 to 2.8 for wing leading-edge sweep angles from 52.5 deg to 75 deg. From the flow-visualization data, the lee-side flows were classified into seven distinct types and a chart was developed that defines the flow mechanism as a function of the conditions normal to the wing leading edge, specifically, angle of attack and Mach number. Pressure data obtained experimentally and by a semiempirical prediction method were employed to investigate the effects of angle of attack, leading-edge sweep, and Mach number on vortex strength and vortex position. In general, the predicted and measured values of vortex-induced normal force and vortex position obtained from experimental data have the same trends with angle of attack, Mach number, and leading-edge sweep; however, the vortex-induced normal force is underpredicted by 15 to 30 percent, and the vortex spanwise location is overpredicted by approximately 15 percent.

Development of High Speed Imaging and Analysis Techniques Compressible Dynamics Stall

NASA Technical Reports Server (NTRS)

Chandrasekhara, M. S.; Carr, L. W.; Wilder, M. C.; Davis, Sanford S. (Technical Monitor)

1996-01-01

Dynamic stall has limited the flight envelope of helicopters for many years. The problem has been studied in the laboratory as well as in flight, but most research, even in the laboratory, has been restricted to surface measurement techniques such as pressure transducers or skin friction gauges, except at low speed. From this research, it became apparent that flow visualization tests performed at Mach numbers representing actual flight conditions were needed if the complex physics associated with dynamic stall was to be properly understood. However, visualization of the flow field during compressible conditions required carefully aligned and meticulously reconstructed holographic interferometry. As part of a long-range effort focused on exposing of the physics of compressible dynamic stall, a research wind tunnel was developed at NASA Ames Research Center which permits visual access to the full flow field surrounding an oscillating airfoil during compressible dynamic stall. Initially, a stroboscopic schlieren technique was used for visualization of the stall process, but the primary research tool has been point diffraction interferometry(PDI), a technique carefully optimized for use in th is project. A review of the process of development of PDI will be presented in the full paper. One of the most valuable aspects of PDI is the fact that interferograms are produced in real time on a continuous basis. The use of a rapidly-pulsed laser makes this practical; a discussion of this approach will be presented in the full paper. This rapid pulsing(up to 40,000 pulses/sec) produces interferograms of the rapidly developing dynamic stall field in sufficient resolution(both in space and time) that the fluid physics of the compressible dynamic stall flowfield can be quantitatively determined, including the gradients of pressure in space and time. This permits analysis of the influence of the effect of pitch rate, Mach number, Reynolds number, amplitude of oscillation, and other parameters on the dynamic stall process. When interferograms can be captured in real time, the potential for real-time mapping of a developing unsteady flow such as dynamic stall becomes a possibility. This has been achieved in the present case through the use of a high-speed drum camera combined with electronic circuitry which has resulted in a series of interferograms obtained during a single cycle of dynamic stall; images obtained at the rate of 20 KHz will be presented as a part of the formal presentation. Interferometry has been available for a long time; however, most of its use has been limited to visualization. The present research has focused on use of interferograms for quantitative mapping of the flow over oscillating airfoils. Instantaneous pressure distributions can now be obtained semi-automatically, making practical the analysis of the thousands of interferograms that are produced in this research. A review of the techniques that have been developed as part of this research effort will be presented in the final paper.

Plasma-Assisted Control of Mach-2 Flowfield over Ramp Geometry

NASA Astrophysics Data System (ADS)

Watanabe, Yasumasa; Leonov, Sergey B.; Houpt, Alec; Hedlund, Brock E.; Elliott, Skye

2017-10-01

This study examined the effect of Reynolds number on plasma-assisted flow control ahead of a compression ramp geometry in Mach-2 supersonic flow. The experiments were conducted in the supersonic wind tunnel SBR-50 at the University of Notre Dame. Stagnation temperature and pressure were varied as T0=294-500K and P0=1-3bar to attain Reynolds number ranging from 3.4×105-2.2×106. Ramp pressure measurements, schlieren visualization, and high-speed camera imaging were used for the evaluation of plasma-assisted flow control effects. A linear dependency was found between the ramp pressure change per averaged plasma power and Reynolds number.

Low-speed longitudinal aerodynamic characteristics of a flat-plate planform model of an advanced fighter configuration

NASA Technical Reports Server (NTRS)

Mcgrath, Brian E.; Neuhart, Dan H.; Gatlin, Gregory M.; Oneil, Pat

1994-01-01

A flat-plate wind tunnel model of an advanced fighter configuration was tested in the NASA LaRC Subsonic Basic Research Tunnel and the 16- by 24-inch Water Tunnel. The test objectives were to obtain and evaluate the low-speed longitudinal aerodynamic characteristics of a candidate configuration for the integration of several new innovative wing designs. The flat plate test allowed for the initial evaluation of the candidate planform and was designated as the baseline planform for the innovative wing design study. Low-speed longitudinal aerodynamic data were obtained over a range of freestream dynamic pressures from 7.5 psf to 30 psf (M = 0.07 to M = 0.14) and angles-of-attack from 0 to 40 deg. The aerodynamic data are presented in coefficient form for the lift, induced drag, and pitching moment. Flow-visualization results obtained were photographs of the flow pattern over the flat plate model in the water tunnel for angles-of-attack from 10 to 40 deg. The force and moment coefficients and the flow-visualization photographs showed the linear and nonlinear aerodynamic characteristics due to attached flow and vortical flow over the flat plate model. Comparison between experiment and linear theory showed good agreement for the lift and induced drag; however, the agreement was poor for the pitching moment.

Wave structure in the radial film flow with a circular hydraulic jump

NASA Astrophysics Data System (ADS)

Rao, A.; Arakeri, J. H.

A circular hydraulic jump is commonly seen when a circular liquid jet impinges on a horizontal plate. Measurements of the film thickness, jump radius and the wave structure for various jet Reynolds numbers are reported. Film thickness measurements are made using an electrical contact method for regions both upstream and downstream of the jump over circular plates without a barrier at the edge. The jump radius and the separation bubble length are measured for various flow rates, plate edge conditions, and radii. Flow visualization using high-speed photography is used to study wave structure and transition. Waves on the jet amplify in the film region upstream of the jump. At high flow rates, the waves amplify enough to cause three-dimensional breakdown and what seems like transition to turbulence. This surface wave induced transition is different from the traditional route and can be exploited to enhance heat and mass transfer rates.

Diving-flight aerodynamics of a peregrine falcon (Falco peregrinus).

PubMed

Ponitz, Benjamin; Schmitz, Anke; Fischer, Dominik; Bleckmann, Horst; Brücker, Christoph

2014-01-01

This study investigates the aerodynamics of the falcon Falco peregrinus while diving. During a dive peregrines can reach velocities of more than 320 km h⁻¹. Unfortunately, in freely roaming falcons, these high velocities prohibit a precise determination of flight parameters such as velocity and acceleration as well as body shape and wing contour. Therefore, individual F. peregrinus were trained to dive in front of a vertical dam with a height of 60 m. The presence of a well-defined background allowed us to reconstruct the flight path and the body shape of the falcon during certain flight phases. Flight trajectories were obtained with a stereo high-speed camera system. In addition, body images of the falcon were taken from two perspectives with a high-resolution digital camera. The dam allowed us to match the high-resolution images obtained from the digital camera with the corresponding images taken with the high-speed cameras. Using these data we built a life-size model of F. peregrinus and used it to measure the drag and lift forces in a wind-tunnel. We compared these forces acting on the model with the data obtained from the 3-D flight path trajectory of the diving F. peregrinus. Visualizations of the flow in the wind-tunnel uncovered details of the flow structure around the falcon's body, which suggests local regions with separation of flow. High-resolution pictures of the diving peregrine indicate that feathers pop-up in the equivalent regions, where flow separation in the model falcon occurred.

High speed flow cytometric separation of viable cells

DOEpatents

Sasaki, D.T.; Van den Engh, G.J.; Buckie, A.M.

1995-11-14

Hematopoietic cell populations are separated to provide cell sets and subsets as viable cells with high purity and high yields, based on the number of original cells present in the mixture. High-speed flow cytometry is employed using light characteristics of the cells to separate the cells, where high flow speeds are used to reduce the sorting time.

High speed flow cytometric separation of viable cells

DOEpatents

Sasaki, Dennis T.; Van den Engh, Gerrit J.; Buckie, Anne-Marie

1995-01-01

Hematopoietic cell populations are separated to provide cell sets and subsets as viable cells with high purity and high yields, based on the number of original cells present in the mixture. High-speed flow cytometry is employed using light characteristics of the cells to separate the cells, where high flow speeds are used to reduce the sorting time.

Visualizing Coolant Flow in Sodium Reactor Subassemblies

DOE Office of Scientific and Technical Information (OSTI.GOV)

None

2010-01-01

Uniformity of temperature controls peak power output. Interchannel cross-flow is the principal cross-assembly energy transport mechanism. The areas of fastest flow all occur at the exterior of the assembly. Further, the fast moving region winds around the assembly in a continuous swath. This Nek5000 simulation uses an unstructured mesh with over one billion grid points, resulting in five billion degrees of freedom per time slice. High speed patches of turbulence due to vertex shedding downstream of the wires persist for about a quarter of the wire-wrap periodic length. Credits: Science: Paul Fisher and Aleks Obabko, Argonne National Laboratory. Visualization: Hankmore » Childs and Janet Jacobsen, Lawrence Berkeley National Laboratory. This research used resources of the Argonne Leadership Computing Facility at Argonne National Laboratory, which is supported by the Office of Science of the U.S. Dept. of Energy under contract DE-AC02-06CH11357. This research was sponsored by the Department of Energy's Office of Nuclear Energy's NEAMS program.« less

Animating streamlines with repeated asymmetric patterns for steady flow visualization

NASA Astrophysics Data System (ADS)

Yeh, Chih-Kuo; Liu, Zhanping; Lee, Tong-Yee

2012-01-01

Animation provides intuitive cueing for revealing essential spatial-temporal features of data in scientific visualization. This paper explores the design of Repeated Asymmetric Patterns (RAPs) in animating evenly-spaced color-mapped streamlines for dense accurate visualization of complex steady flows. We present a smooth cyclic variable-speed RAP animation model that performs velocity (magnitude) integral luminance transition on streamlines. This model is extended with inter-streamline synchronization in luminance varying along the tangential direction to emulate orthogonal advancing waves from a geometry-based flow representation, and then with evenly-spaced hue differing in the orthogonal direction to construct tangential flow streaks. To weave these two mutually dual sets of patterns, we propose an energy-decreasing strategy that adopts an iterative yet efficient procedure for determining the luminance phase and hue of each streamline in HSL color space. We also employ adaptive luminance interleaving in the direction perpendicular to the flow to increase the contrast between streamlines.

Comparison of electrical capacitance tomography and gamma densitometer measurement in viscous oil-gas flows

DOE Office of Scientific and Technical Information (OSTI.GOV)

Archibong Eso, A.; Zhao, Yabin; Yeung, Hoi

2014-04-11

Multiphase flow is a common occurrence in industries such as nuclear, process, oil and gas, food and chemical. A prior knowledge of its features and characteristics is essential in the design, control and management of such processes due to its complex nature. Electrical Capacitance Tomography (ECT) and Gamma Densitometer (Gamma) are two promising approaches for multiphase visualization and characterization in process industries. In two phase oil and gas flow, ECT and Gamma are used in multiphase flow monitoring techniques due to their inherent simplicity, robustness, and an ability to withstand wide range of operational temperatures and pressures. High viscous oilmore » (viscosity > 100 cP) is of interest because of its huge reserves, technological advances in its production and unlike conventional oil (oil viscosity < 100 cP) and gas flows where ECT and Gamma have been previously used, high viscous oil and gas flows comes with certain associated concerns which include; increased entrainment of gas bubbles dispersed in oil, shorter and more frequent slugs as well as oil film coatings on the walls of flowing conduits. This study aims to determine the suitability of both devices in the visualization and characterization of high-viscous oil and gas flow. Static tests are performed with both devices and liquid holdup measurements are obtained. Dynamic experiments were also conducted in a 1 and 3 inch facility at Cranfield University with a range of nominal viscosities (1000, 3000 and 7500 cP). Plug, slug and wavy annular flow patterns were identified by means of Probability Mass Function and time series analysis of the data acquired from Gamma and ECT devices with high speed camera used to validate the results. Measured Liquid holdups for both devices were also compared.« less

Comparison of electrical capacitance tomography & gamma densitometer measurement in viscous oil-gas flows

NASA Astrophysics Data System (ADS)

Archibong Eso, A.; Zhao, Yabin; Yeung, Hoi

2014-04-01

Multiphase flow is a common occurrence in industries such as nuclear, process, oil & gas, food and chemical. A prior knowledge of its features and characteristics is essential in the design, control and management of such processes due to its complex nature. Electrical Capacitance Tomography (ECT) and Gamma Densitometer (Gamma) are two promising approaches for multiphase visualization and characterization in process industries. In two phase oil & gas flow, ECT and Gamma are used in multiphase flow monitoring techniques due to their inherent simplicity, robustness, and an ability to withstand wide range of operational temperatures and pressures. High viscous oil (viscosity > 100 cP) is of interest because of its huge reserves, technological advances in its production and unlike conventional oil (oil viscosity < 100 cP) and gas flows where ECT and Gamma have been previously used, high viscous oil and gas flows comes with certain associated concerns which include; increased entrainment of gas bubbles dispersed in oil, shorter and more frequent slugs as well as oil film coatings on the walls of flowing conduits. This study aims to determine the suitability of both devices in the visualization and characterization of high-viscous oil and gas flow. Static tests are performed with both devices and liquid holdup measurements are obtained. Dynamic experiments were also conducted in a 1 & 3 inch facility at Cranfield University with a range of nominal viscosities (1000, 3000 & 7500 cP). Plug, slug and wavy annular flow patterns were identified by means of Probability Mass Function and time series analysis of the data acquired from Gamma and ECT devices with high speed camera used to validate the results. Measured Liquid holdups for both devices were also compared.

Simulated self-motion in a visual gravity field: sensitivity to vertical and horizontal heading in the human brain.

PubMed

Indovina, Iole; Maffei, Vincenzo; Pauwels, Karl; Macaluso, Emiliano; Orban, Guy A; Lacquaniti, Francesco

2013-05-01

Multiple visual signals are relevant to perception of heading direction. While the role of optic flow and depth cues has been studied extensively, little is known about the visual effects of gravity on heading perception. We used fMRI to investigate the contribution of gravity-related visual cues on the processing of vertical versus horizontal apparent self-motion. Participants experienced virtual roller-coaster rides in different scenarios, at constant speed or 1g-acceleration/deceleration. Imaging results showed that vertical self-motion coherent with gravity engaged the posterior insula and other brain regions that have been previously associated with vertical object motion under gravity. This selective pattern of activation was also found in a second experiment that included rectilinear motion in tunnels, whose direction was cued by the preceding open-air curves only. We argue that the posterior insula might perform high-order computations on visual motion patterns, combining different sensory cues and prior information about the effects of gravity. Medial-temporal regions including para-hippocampus and hippocampus were more activated by horizontal motion, preferably at constant speed, consistent with a role in inertial navigation. Overall, the results suggest partially distinct neural representations of the cardinal axes of self-motion (horizontal and vertical). Copyright © 2013 Elsevier Inc. All rights reserved.

A Motion-Based Feature for Event-Based Pattern Recognition

PubMed Central

Clady, Xavier; Maro, Jean-Matthieu; Barré, Sébastien; Benosman, Ryad B.

2017-01-01

This paper introduces an event-based luminance-free feature from the output of asynchronous event-based neuromorphic retinas. The feature consists in mapping the distribution of the optical flow along the contours of the moving objects in the visual scene into a matrix. Asynchronous event-based neuromorphic retinas are composed of autonomous pixels, each of them asynchronously generating “spiking” events that encode relative changes in pixels' illumination at high temporal resolutions. The optical flow is computed at each event, and is integrated locally or globally in a speed and direction coordinate frame based grid, using speed-tuned temporal kernels. The latter ensures that the resulting feature equitably represents the distribution of the normal motion along the current moving edges, whatever their respective dynamics. The usefulness and the generality of the proposed feature are demonstrated in pattern recognition applications: local corner detection and global gesture recognition. PMID:28101001

Ethylene Trace-gas Techniques for High-speed Flows

NASA Technical Reports Server (NTRS)

Davis, David O.; Reichert, Bruce A.

1994-01-01

Three applications of the ethylene trace-gas technique to high-speed flows are described: flow-field tracking, air-to-air mixing, and bleed mass-flow measurement. The technique involves injecting a non-reacting gas (ethylene) into the flow field and measuring the concentration distribution in a downstream plane. From the distributions, information about flow development, mixing, and mass-flow rates can be dtermined. The trace-gas apparatus and special considerations for use in high-speed flow are discussed. A description of each application, including uncertainty estimates is followed by a demonstrative example.

Visualizing microvascular flow variation in OCTA using variable interscan time analysis (VISTA) (Conference Presentation)

NASA Astrophysics Data System (ADS)

Moult, Eric M.; Ploner, Stefan A.; Choi, WooJhon; Lee, ByungKun; Husvogt, Lennart A.; Lu, Chen D.; Novais, Eduardo; Cole, Emily D.; Potsaid, Benjamin M.; Duker, Jay S.; Hornegger, Joachim; Meier, Andreas K.; Waheed, Nadia K.; Fujimoto, James G.

2017-02-01

OCT angiography (OCTA) has recently garnered immense interest in clinical ophthalmology, permitting ocular vasculature to be viewed in exquisite detail, in vivo, and without the injection of exogenous dyes. However, commercial OCTA systems provide little information about actual erythrocyte speeds; instead, OCTA is typically used to visualize the presence and/or absence of vasculature. This is an important limitation because in many ocular diseases, including diabetic retinopathy (DR) and age-related macular degeneration (AMD), alterations in blood flow, but not necessarily only the presence or absence of vasculature, are thought to be important in understanding pathogenesis. To address this limitation, we have developed an algorithm, variable interscan time analysis (VISTA), which is capable of resolving different erythrocyte speeds. VISTA works by acquiring >2 repeated B-scans, and then computing multiple OCTA signals corresponding to different effective interscan times. The OCTA signals corresponding to different effective interscan times contain independent information about erythrocyte speed. In this study we provide a theoretical overview of VISTA, and investigate the utility of VISTA in studying blood flow alterations in ocular disease. OCTA-VISTA images of eyes with choroidal neovascularization, geographic atrophy, and diabetic retinopathy are presented.

A biomimetic vision-based hovercraft accounts for bees' complex behaviour in various corridors.

PubMed

Roubieu, Frédéric L; Serres, Julien R; Colonnier, Fabien; Franceschini, Nicolas; Viollet, Stéphane; Ruffier, Franck

2014-09-01

Here we present the first systematic comparison between the visual guidance behaviour of a biomimetic robot and those of honeybees flying in similar environments. We built a miniature hovercraft which can travel safely along corridors with various configurations. For the first time, we implemented on a real physical robot the 'lateral optic flow regulation autopilot', which we previously studied computer simulations. This autopilot inspired by the results of experiments on various species of hymenoptera consists of two intertwined feedback loops, the speed and lateral control loops, each of which has its own optic flow (OF) set-point. A heading-lock system makes the robot move straight ahead as fast as 69 cm s(-1) with a clearance from one wall as small as 31 cm, giving an unusually high translational OF value (125° s(-1)). Our biomimetic robot was found to navigate safely along straight, tapered and bent corridors, and to react appropriately to perturbations such as the lack of texture on one wall, the presence of a tapering or non-stationary section of the corridor and even a sloping terrain equivalent to a wind disturbance. The front end of the visual system consists of only two local motion sensors (LMS), one on each side. This minimalistic visual system measuring the lateral OF suffices to control both the robot's forward speed and its clearance from the walls without ever measuring any speeds or distances. We added two additional LMSs oriented at +/-45° to improve the robot's performances in stiffly tapered corridors. The simple control system accounts for worker bees' ability to navigate safely in six challenging environments: straight corridors, single walls, tapered corridors, straight corridors with part of one wall moving or missing, as well as in the presence of wind.

A Dynamic Bayesian Observer Model Reveals Origins of Bias in Visual Path Integration.

PubMed

Lakshminarasimhan, Kaushik J; Petsalis, Marina; Park, Hyeshin; DeAngelis, Gregory C; Pitkow, Xaq; Angelaki, Dora E

2018-06-20

Path integration is a strategy by which animals track their position by integrating their self-motion velocity. To identify the computational origins of bias in visual path integration, we asked human subjects to navigate in a virtual environment using optic flow and found that they generally traveled beyond the goal location. Such a behavior could stem from leaky integration of unbiased self-motion velocity estimates or from a prior expectation favoring slower speeds that causes velocity underestimation. Testing both alternatives using a probabilistic framework that maximizes expected reward, we found that subjects' biases were better explained by a slow-speed prior than imperfect integration. When subjects integrate paths over long periods, this framework intriguingly predicts a distance-dependent bias reversal due to buildup of uncertainty, which we also confirmed experimentally. These results suggest that visual path integration in noisy environments is limited largely by biases in processing optic flow rather than by leaky integration. Copyright © 2018 Elsevier Inc. All rights reserved.

Experimental Investigation of Subsonic Turbulent Boundary Layer Flow Over a Wall-Mounted Axisymmetric Hill

NASA Technical Reports Server (NTRS)

Bell, James H.; Heineck, James T.; Zilliac, Gregory; Mehta, Rabindra D.; Long, Kurtis R.

2016-01-01

An important goal for modern fluid mechanics experiments is to provide datasets which present a challenge for Computational Fluid Dynamics simulations to reproduce. Such "CFD validation experiments" should be well-characterized and well-documented, and should investigate flows which are difficult for CFD to calculate. It is also often convenient for the experiment to be challenging for CFD in some aspects while simple in others. This report is part of the continuing documentation of a series of experiments conducted to characterize the flow around an axisymmetric, modified-cosine-shaped, wall-mounted hill named "FAITH" (Fundamental Aero Investigates The Hill). Computation of this flow is easy in some ways - subsonic flow over a simple shape - while being complex in others - separated flow and boundary layer interactions. The primary set of experiments were performed on a 15.2 cm high, 45.7 cm base diameter machined aluminum model that was tested at mean speeds of 50 m/s (Reynolds Number based on height = 500,000). The ratio of model height to boundary later height was approximately 3. The flow was characterized using surface oil flow visualization, Cobra probe to determine point-wise steady and unsteady 3D velocities, Particle Image Velocimetry (PIV) to determine 3D velocities and turbulence statistics along specified planes, Pressure Sensitive Paint (PSP) to determine mean surface pressures, and Fringe Imaging Skin Friction (FISF) to determine surface skin friction magnitude and direction. A set of pathfinder experiments were also performed in a water channel on a smaller scale (5.1 cm high, 15.2 cm base diameter) sintered nylon model. The water channel test was conducted at a mean test section speed of 3 cm/s (Reynolds Number of 1500), but at the same ratio of model height to boundary layer thickness. Dye injection from both the model and an upstream rake was used to visualize the flow. This report summarizes the experimental set-up, techniques used, and data acquired. It also describes some details of the dataset that is being constructed for use by other researchers, especially the CFD community.

Flow visualization of acoustic levitation experiment

NASA Technical Reports Server (NTRS)

Baroth, ED

1987-01-01

Acoustic levitation experiments for space applications were performed. Holographic interferometry is being used to study the heat transfer rates on a heated rod enclosed in a 6 cu in chamber. Acoustic waves at levels up to 150 db increased the heating rates to the rod by factors of three to four. High speed real time holographic interferometry was used to measure the boundary layer on the heated rod. Data reduction and digitization of the interferograms are being implemented.

Aerodynamics of High-Lift Configuration Civil Aircraft Model in JAXA

NASA Astrophysics Data System (ADS)

Yokokawa, Yuzuru; Murayama, Mitsuhiro; Ito, Takeshi; Yamamoto, Kazuomi

This paper presents basic aerodynamics and stall characteristics of the high-lift configuration aircraft model JSM (JAXA Standard Model). During research process of developing high-lift system design method, wind tunnel testing at JAXA 6.5m by 5.5m low-speed wind tunnel and Navier-Stokes computation on unstructured hybrid mesh were performed for a realistic configuration aircraft model equipped with high-lift devices, fuselage, nacelle-pylon, slat tracks and Flap Track Fairings (FTF), which was assumed 100 passenger class modern commercial transport aircraft. The testing and the computation aimed to understand flow physics and then to obtain some guidelines for designing a high performance high-lift system. As a result of the testing, Reynolds number effects within linear region and stall region were observed. Analysis of static pressure distribution and flow visualization gave the knowledge to understand the aerodynamic performance. CFD could capture the whole characteristics of basic aerodynamics and clarify flow mechanism which governs stall characteristics even for complicated geometry and its flow field. This collaborative work between wind tunnel testing and CFD is advantageous for improving or has improved the aerodynamic performance.

Visualization of flows in a motored rotary combustion engine using holographic interferometry

NASA Technical Reports Server (NTRS)

Hicks, Y. R.; Schock, H. J.; Craig, J. E.; Umstatter, H. L.; Lee, D. Y.

1986-01-01

The use of holographic interferometry to view the small- and large-scale flow field structures in the combustion chamber of a motored Wankel engine assembly is described. In order that the flow patterns of interest could be observed, small quantities of helium were injected with the intake air. Variation of the air flow patterns with engine speed, helium flow rate, and rotor position are described. The air flow at two locations within the combustion chamber was examined using this technique.

Computer-animated stimuli to measure motion sensitivity: constraints on signal design in the Jacky dragon.

PubMed

Woo, Kevin L; Rieucau, Guillaume; Burke, Darren

2017-02-01

Identifying perceptual thresholds is critical for understanding the mechanisms that underlie signal evolution. Using computer-animated stimuli, we examined visual speed sensitivity in the Jacky dragon Amphibolurus muricatus , a species that makes extensive use of rapid motor patterns in social communication. First, focal lizards were tested in discrimination trials using random-dot kinematograms displaying combinations of speed, coherence, and direction. Second, we measured subject lizards' ability to predict the appearance of a secondary reinforcer (1 of 3 different computer-generated animations of invertebrates: cricket, spider, and mite) based on the direction of movement of a field of drifting dots by following a set of behavioural responses (e.g., orienting response, latency to respond) to our virtual stimuli. We found an effect of both speed and coherence, as well as an interaction between these 2 factors on the perception of moving stimuli. Overall, our results showed that Jacky dragons have acute sensitivity to high speeds. We then employed an optic flow analysis to match the performance to ecologically relevant motion. Our results suggest that the Jacky dragon visual system may have been shaped to detect fast motion. This pre-existing sensitivity may have constrained the evolution of conspecific displays. In contrast, Jacky dragons may have difficulty in detecting the movement of ambush predators, such as snakes and of some invertebrate prey. Our study also demonstrates the potential of the computer-animated stimuli technique for conducting nonintrusive tests to explore motion range and sensitivity in a visually mediated species.

Modeling unsteady sound refraction by coherent structures in a high-speed jet

NASA Astrophysics Data System (ADS)

Kan, Pinqing; Lewalle, Jacques

2011-11-01

We construct a visual model for the unsteady refraction of sound waves from point sources in a Ma = 0.6 jet. The mass and inviscid momentum equations give an equation governing acoustic fluctuations, including anisotropic propagation, attenuation and sources; differences with Lighthill's equation will be discussed. On this basis, the theory of characteristics gives canonical equations for the acoustic paths from any source into the far field. We model a steady mean flow in the near-jet region including the potential core and the mixing region downstream of its collapse, and model the convection of coherent structures as traveling wave perturbations of this mean flow. For a regular distribution of point sources in this region, we present a visual rendition of fluctuating distortion, lensing and deaf spots from the viewpoint of a far-field observer. Supported in part by AFOSR Grant FA-9550-10-1-0536 and by a Syracuse University Graduate Fellowship.

Visual and psychological stress during computer work in healthy, young females-physiological responses.

PubMed

Mork, Randi; Falkenberg, Helle K; Fostervold, Knut Inge; Thorud, Hanne Mari S

2018-05-30

Among computer workers, visual complaints, and neck pain are highly prevalent. This study explores how occupational simulated stressors during computer work, like glare and psychosocial stress, affect physiological responses in young females with normal vision. The study was a within-subject laboratory experiment with a counterbalanced, repeated design. Forty-three females performed four 10-min computer-work sessions with different stress exposures: (1) minimal stress; (2) visual stress (direct glare); (3) psychological stress; and (4) combined visual and psychological stress. Muscle activity and muscle blood flow in trapezius, muscle blood flow in orbicularis oculi, heart rate, blood pressure, blink rate and postural angles were continuously recorded. Immediately after each computer-work session, fixation disparity was measured and a questionnaire regarding perceived workstation lighting and stress was completed. Exposure to direct glare resulted in increased trapezius muscle blood flow, increased blink rate, and forward bending of the head. Psychological stress induced a transient increase in trapezius muscle activity and a more forward-bent posture. Bending forward towards the computer screen was correlated with higher productivity (reading speed), indicating a concentration or stress response. Forward bent posture was also associated with changes in fixation disparity. Furthermore, during computer work per se, trapezius muscle activity and blood flow, orbicularis oculi muscle blood flow, and heart rate were increased compared to rest. Exposure to glare and psychological stress during computer work were shown to influence the trapezius muscle, posture, and blink rate in young, healthy females with normal binocular vision, but in different ways. Accordingly, both visual and psychological factors must be taken into account when optimizing computer workstations to reduce physiological responses that may cause excessive eyestrain and musculoskeletal load.

Flow Induced Noise from Turbulent Flow over Steps and Gaps

DTIC Science & Technology

2010-05-04

Wall Jet Facility which is detailed in Figures 2.1 through 2.3. In this facility a Cincinnati Fan variable speed centrifugal fan with model number...the flow over the multiple backward steps considered in this study The following subsections will concentrate on the oil flow visualization performed ...NUMBER 5e. TASK NUMBER 5f. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Virginia Polytechnic Institute and State University

Shock Characteristics Measured Upstream of Both a Forward-Swept and an Aft-Swept Fan

NASA Technical Reports Server (NTRS)

Podboy, Gary G.; Krupar, Martin J.; Sutliff, Daniel L.; Horvath, Csaba

2007-01-01

Three different types of diagnostic data-blade surface flow visualization, shroud unsteady pressure, and laser Doppler velocimeter (LDV)--were obtained on two fans, one forward-swept and one aft-swept, in order to learn more about the shocks which propagate upstream of these rotors when they are operated at transonic tip speeds. Flow visualization data are presented for the forward-swept fan operating at 13831 rpm(sub c), and for the aft-swept fan operating at 12500 and 13831 rpm(sub c) (corresponding to tip rotational Mach numbers of 1.07 and 1.19, respectively). The flow visualization data identify where the shocks occur on the suction side of the rotor blades. These data show that at the takeoff speed, 13831 rpm(sub c), the shocks occurring in the tip region of the forward-swept fan are further downstream in the blade passage than with the aft-swept fan. Shroud unsteady pressure measurements were acquired using a linear array of 15 equally-spaced pressure transducers extending from two tip axial chords upstream to 0.8 tip axial chords downstream of the static position of the tip leading edge of each rotor. Such data are presented for each fan operating at one subsonic and five transonic tip speeds. The unsteady pressure data show relatively strong detached shocks propagating upstream of the aft-swept rotor at the three lowest transonic tip speeds, and weak, oblique pressure disturbances attached to the tip of the aft-swept fan at the two highest transonic tip speeds. The unsteady pressure measurements made with the forward-swept fan do not show strong shocks propagating upstream of that rotor at any of the tested speeds. A comparison of the forward-swept and aft-swept shroud unsteady pressure measurements indicates that at any given transonic speed the pressure disturbance just upstream of the tip of the forward-swept fan is much weaker than that of the aft-swept fan. The LDV data suggest that at 12500 and 13831 rpm(sub c), the forward-swept fan swallowed the passage shocks occurring in the tip region of the blades, whereas the aft-swept fan did not. Due to this difference, the flows just upstream of the two fans were found to be quite different at both of these transonic speeds. Nevertheless, despite distinct differences just upstream of the two rotors, the two fan flows were much more alike about one axial blade chord further upstream. As a result, the LDV data suggest that it is unwise to attempt to determine the effect that the shocks have on far field noise by focusing only on measurements (or CFD predictions) made very near the rotor. Instead, these data suggest that it is important to track the shocks throughout the inlet.

Virtual Reality as a Medium for Sensorimotor Adaptation Training and Spaceflight Countermeasures

NASA Technical Reports Server (NTRS)

Madansingh, S.; Bloomberg, J. J.

2014-01-01

Astronauts experience a profound sensorimotor adaptation during transition to and from the microgravity environment of space. With the upcoming shift to extra-long duration missions (upwards of 1 year) aboard the International Space Station, the immediate risks to astronauts during these transitory periods become more important than ever to understand and prepare for. Recent advances in virtual reality technology enable everyday adoption of these tools for entertainment and use in training. Embedding an individual in a virtual environment (VE) allows the ability to change the perception of visual flow, elicit automatic motor behavior and produce sensorimotor adaptation, not unlike those required during long duration microgravity exposure. The overall goal of this study is to determine the feasibility of present head mounted display technology (HMD) to produce reliable visual flow information and the expected adaptation associated with virtual environment manipulation to be used in future sensorimotor adaptability countermeasures. To further understand the influence of visual flow on gait adaptation during treadmill walking, a series of discordant visual flow manipulations in a virtual environment are proposed. Six healthy participants (3 male and 3 female) will observe visual flow information via HMD (Oculus Rift DK2) while walking on an instrumented treadmill at their preferred walking speed. Participants will be immersed in a series of VE's resembling infinite hallways with different visual characteristics: an office hallway, a hallway with pillars and the hallway of a fictional spacecraft. Participants will perform three trials of 10 min. each, which include walking on the treadmill while receiving congruent or incongruent visual information via the HMD. In the first trial, participants will experience congruent visual information (baseline) where the hallway is perceived to move at the same rate as their walking speed. The final two trials will be randomized among participants where the hallway is perceived to move at either half (0.5x) or twice (2.0x) their preferred walking speed. Participants will remain on the treadmill between trials and will not be warned of the upcoming change to visual flow to minimize preparatory adjustments. Stride length, step frequency and dual-support time will be quantified during each trial. We hypothesize that participants will experience a rapid modification in gait performance during periods of adaptive change, expressed as a decrease in step length, an increase in step frequency and an increase in dual-support time, followed by a period of adaptation where these movement parameters will return to near-baseline levels. As stride length, step frequency and dual support times return to baseline values, an adaptation time constant will be derived to establish individual time-to-adapt (TTA). HMD technology represents a paradigm shift in sensorimotor adaptation training where gait adaptability can be stressed using off-the-shelf consumer products and minimal experimental equipment, allowing for greater training flexibility in astronaut and terrestrial applications alike.

Feeding Currents generated by Cassiopea jellyfish

NASA Astrophysics Data System (ADS)

Gaddam, M. G.; Santhanakrishnan, A.

2016-02-01

Feeding currents generated by organisms dwelling in the benthic boundary layer can enhance nutrient fluxes in coastal habitats with low-speed ambient flows. Patchy aggregations of Cassiopea medusae, commonly referred to as the "upside-down" jellyfish, are seen in sheltered marine environments such as mangrove forests and coral reefs in shallow regions saturated with sunlight. They exhibit a sessile, non-swimming lifestyle, and are oriented such that their bells are attached to the substrate and oral arms directed toward the free surface. Pulsations of their bells drive flow toward and away from the body, assisting in suspension feeding and for exchange of inorganic and organic matter across the water column. The feeding currents generated by aggregations of these medusae and subsequent effects on mixing in the water column have not been examined. We experimentally investigated currents generated by groups of Cassiopea medusae in a low-speed recirculating water tunnel. Multiple medusae grouping arrangements were tested in the tunnel based on time-lapse videos of the organisms obtained overnight in laboratory aquaria. Fluorescent dye introduced underneath the substrate was used to investigate release of porewater via bell motion. Quantitative flow visualization studies of Cassiopea currents were conducted using 2D high-speed particle image velocimetry. Vertical mixing of medusa-induced jets were observed in the presence of minimal background flow. The implications of feeding currents generated by groups of Cassiopea medusae on mixing in the water column will be presented.

The temperature measurement research for high-speed flow based on tunable diode laser absorption spectroscopy

NASA Astrophysics Data System (ADS)

Di, Yue; Jin, Yi; Jiang, Hong-liang; Zhai, Chao

2013-09-01

Due to the particularity of the high-speed flow, in order to accurately obtain its' temperature, the measurement system should has some characteristics of not interfereing with the flow, non-contact measurement and high time resolution. The traditional measurement method cannot meet the above requirements, however the measurement method based on tunable diode laser absorption spectroscopy (TDLAS) technology can meet the requirements for high-speed flow temperature measurement. When the near-infared light of a specific frequency is through the media to be measured, it will be absorbed by the water vapor molecules and then the transmission light intensity is detected by the detector. The temperature of the water vapor which is also the high-speed flow temperature, can be accurately obtained by the Beer-Lambert law. This paper focused on the research of absorption spectrum method for high speed flow temperature measurement with the scope of 250K-500K. Firstly, spectral line selection method for low temperature measurement of high-speed flow is discussed. Selected absorption lines should be isolated and have a high peak absorption within the range of 250-500K, at the same time the interference of the other lines should be avoided, so that a high measurement accuracy can be obtained. According to the near-infrared absorption spectra characteristics of water vapor, four absorption lines at the near 1395 nm and 1409 nm are selected. Secondly, a system for the temperature measurement of the water vapor in the high-speed flow is established. Room temperature are measured through two methods, direct absorption spectroscopy (DAS) and wavelength modulation spectroscopy (WMS) ,the results show that this system can realize on-line measurement of the temperature and the measurement error is about 3%. Finally, the system will be used for temperature measurement of the high-speed flow in the shock tunnel, its feasibility of measurement is analyzed.

Spray Behavior and Atomization Characteristics of Biodiesel

NASA Astrophysics Data System (ADS)

Choi, Seung-Hun; Oh, Young-Taig

Biodiesel has large amount of oxygen in itself, which make it very efficient in reducing exhaust emission by improving combustion inside an engine. But biodiesel has a low temperature flow problem because it has a high viscosity. In this study, the spray behavior and atomization characteristics were investigated to confirm of some effect for the combination of non-esterification biodiesel and fuel additive WDP and IPA. The process of spray was visualized through the visualization system composed of a halogen lamp and high speed camera, and atomization characteristics were investigated through LDPA. When blending WDP and IPA with biodiesel, atomization and spray characteristics were improved. Through this experimental result, SMD of blended fuel, WDP 25% and biodiesel 75%, was 33.9% reduced at distance 6cm from a nozzle tip under injection pressure 30MPa.

Novel full-spectral flow cytometry with multiple spectrally-adjacent fluorescent proteins and fluorochromes and visualization of in vivo cellular movement.

PubMed

Futamura, Koji; Sekino, Masashi; Hata, Akihiro; Ikebuchi, Ryoyo; Nakanishi, Yasutaka; Egawa, Gyohei; Kabashima, Kenji; Watanabe, Takeshi; Furuki, Motohiro; Tomura, Michio

2015-09-01

Flow cytometric analysis with multicolor fluoroprobes is an essential method for detecting biological signatures of cells. Here, we present a new full-spectral flow cytometer (spectral-FCM). Unlike conventional flow cytometer, this spectral-FCM acquires the emitted fluorescence for all probes across the full-spectrum from each cell with 32 channels sequential PMT unit after dispersion with prism, and extracts the signals of each fluoroprobe based on the spectral shape of each fluoroprobe using unique algorithm in high speed, high sensitive, accurate, automatic and real-time. The spectral-FCM detects the continuous changes in emission spectra from green to red of the photoconvertible protein, KikGR with high-spectral resolution and separates spectrally-adjacent fluoroprobes, such as FITC (Emission peak (Em) 519 nm) and EGFP (Em 507 nm). Moreover, the spectral-FCM can measure and subtract autofluorescence of each cell providing increased signal-to-noise ratios and improved resolution of dim samples, which leads to a transformative technology for investigation of single cell state and function. These advances make it possible to perform 11-color fluorescence analysis to visualize movement of multilinage immune cells by using KikGR-expressing mice. Thus, the novel spectral flow cytometry improves the combinational use of spectrally-adjacent various FPs and multicolor fluorochromes in metabolically active cell for the investigation of not only the immune system but also other research and clinical fields of use. © 2015 International Society for Advancement of Cytometry.

Diving-Flight Aerodynamics of a Peregrine Falcon (Falco peregrinus)

PubMed Central

Ponitz, Benjamin; Schmitz, Anke; Fischer, Dominik; Bleckmann, Horst; Brücker, Christoph

2014-01-01

This study investigates the aerodynamics of the falcon Falco peregrinus while diving. During a dive peregrines can reach velocities of more than 320 km h−1. Unfortunately, in freely roaming falcons, these high velocities prohibit a precise determination of flight parameters such as velocity and acceleration as well as body shape and wing contour. Therefore, individual F. peregrinus were trained to dive in front of a vertical dam with a height of 60 m. The presence of a well-defined background allowed us to reconstruct the flight path and the body shape of the falcon during certain flight phases. Flight trajectories were obtained with a stereo high-speed camera system. In addition, body images of the falcon were taken from two perspectives with a high-resolution digital camera. The dam allowed us to match the high-resolution images obtained from the digital camera with the corresponding images taken with the high-speed cameras. Using these data we built a life-size model of F. peregrinus and used it to measure the drag and lift forces in a wind-tunnel. We compared these forces acting on the model with the data obtained from the 3-D flight path trajectory of the diving F. peregrinus. Visualizations of the flow in the wind-tunnel uncovered details of the flow structure around the falcon’s body, which suggests local regions with separation of flow. High-resolution pictures of the diving peregrine indicate that feathers pop-up in the equivalent regions, where flow separation in the model falcon occurred. PMID:24505258

Information Points and Optimal Discharging Speed: Effects on the Saturation Flow at Signalized Intersections

ERIC Educational Resources Information Center

Gao, Lijun

2015-01-01

An information point was defined in this study as any object, structure, or activity located outside of a traveling vehicle that could potentially attract the visual attention of the driver. Saturation flow rates were studied for three pairs of signalized intersections in Toledo, Ohio. Each pair of intersections consisted of one intersection with…

Low-speed flowfield characterization by infrared measurements of surface temperatures

NASA Technical Reports Server (NTRS)

Gartenberg, E.; Roberts, A. S., Jr.; Mcree, G. J.

1989-01-01

An experimental program was aimed at identifying areas in low speed aerodynamic research where infrared imaging systems can make significant contributions. Implementing a new technique, a long electrically heated wire was placed across a laminar jet. By measuring the temperature distribution along the wire with the IR imaging camera, the flow behavior was identified. Furthermore, using Nusselt number correlations, the velocity distribution could be deduced. The same approach was used to survey wakes behind cylinders in a wind-tunnel. This method is suited to investigate flows with position dependent velocities, e.g., boundary layers, confined flows, jets, wakes, and shear layers. It was found that the IR imaging camera cannot accurately track high gradient temperature fields. A correlation procedure was devised to account for this limitation. Other wind-tunnel experiments included tracking the development of the laminar boundary layer over a warmed flat plate by measuring the chordwise temperature distribution. This technique was applied also to the flow downstream from a rearward facing step. Finally, the IR imaging system was used to study boundary layer behavior over an airfoil at angles of attack from zero up to separation. The results were confirmed with tufts observable both visually and with the IR imaging camera.

Experimental Study of Boundary Layer Flow Control Using an Array of Ramp-Shaped Vortex Generators

NASA Technical Reports Server (NTRS)

Hirt, Stefanie M.; Zaman, Khairul B.M.Q.; Bencic, Tomothy J.

2012-01-01

The objective of this study was to obtain a database on the flowfield past an array of vortex generators (VGs) in a turbulent boundary layer. All testing was carried out in a low speed wind tunnel with a flow velocity of 29 ft/sec, giving a Reynolds number of 17,500 based on the width of the VG. The flowfield generated by an array of five ramp-shaped vortex generators was examined with hot wire anemometry and smoke flow visualization. The magnitude and extent of the velocity increase near the wall, the penetration of the velocity deficit into the core flow, and the peak streamwise vorticity are examined. Influence of various parameters on the effectiveness of the array is considered on the basis of the ability to pull high momentum fluid into the near wall region.

Water flow in high-speed handpieces.

PubMed

Cavalcanti, Bruno Neves; Serairdarian, Paulo Isaías; Rode, Sigmar Mello

2005-05-01

This study measured the water flow commonly used in high-speed handpieces to evaluate the water flow's influence on temperature generation. Different flow speeds were evaluated between turbines that had different numbers of cooling apertures. Two water samples were collected from each high-speed handpiece at private practices and at the School of Dentistry at São José dos Campos. The first sample was collected at the customary flow and the second was collected with the terminal opened for maximum flow. The two samples were collected into weighed glass receptacles after 15 seconds of turbine operation. The glass receptacles were reweighed and the difference between weights was recorded to calculate the water flow in mL/min and for further statistical analysis. The average water flow for 137 samples was 29.48 mL/min. The flow speeds obtained were 42.38 mL/min for turbines with one coolant aperture; 34.31 mL/min for turbines with two coolant apertures; and 30.44 mL/min for turbines with three coolant apertures. There were statistical differences between turbines with one and three coolant apertures (Tukey-Kramer multiple comparisons test with P < .05). Turbine handpieces with one cooling aperture distributed more water for the burs than high-speed handpieces with more than one aperture.

Flow visualization by mobile phone cameras

NASA Astrophysics Data System (ADS)

Cierpka, Christian; Hain, Rainer; Buchmann, Nicolas A.

2016-06-01

Mobile smart phones were completely changing people's communication within the last ten years. However, these devices do not only offer communication through different channels but also devices and applications for fun and recreation. In this respect, mobile phone cameras include now relatively fast (up to 240 Hz) cameras to capture high-speed videos of sport events or other fast processes. The article therefore explores the possibility to make use of this development and the wide spread availability of these cameras in the terms of velocity measurements for industrial or technical applications and fluid dynamics education in high schools and at universities. The requirements for a simplistic PIV (particle image velocimetry) system are discussed. A model experiment of a free water jet was used to prove the concept and shed some light on the achievable quality and determine bottle necks by comparing the results obtained with a mobile phone camera with data taken by a high-speed camera suited for scientific experiments.

Parametric Study of Advanced Mixing of Fuel/Oxidant System in High Speed Gaseous Flows and Experimental Validation Planning

DTIC Science & Technology

2001-08-30

Body with Thermo-Chemical destribution of Heat-Protected System . In: Physical and Gasdynamic Phenomena in Supersonic Flows Over Bodies. Edit. By...Final Report on ISTC Contract # 1809p Parametric Study of Advanced Mixing of Fuel/Oxidant System in High Speed Gaseous Flows and Experimental...of Advanced Mixing of Fuel/Oxidant System in High Speed Gaseous Flows and Experimental Validation Planning 5c. PROGRAM ELEMENT NUMBER 5d. PROJECT

Design and Development of Low-Cost Water Tunnel for Educational Purpose

NASA Astrophysics Data System (ADS)

Zahari, M.; Dol, S. S.

2015-04-01

The hydrodynamic behaviour of immersed body is essential in fluid dynamics study. Water tunnel is an example of facility required to provide a controlled condition for fluid flow research. The operational principle of water tunnel is quite similar to the wind tunnel but with different working fluid and higher flow-pumping capacity. Flow visualization in wind tunnel is more difficult to conduct as turbulent flows in wind dissipate quickly whilst water tunnel is more suitable for such purpose due to higher fluid viscosity and wide variety of visualization techniques can be employed. The present work focusses on the design and development of open flow water tunnel for the purpose of studying vortex-induced vibration from turbulent vortex shedding phenomenon. The water tunnel is designed to provide a steady and uniform flow speed within the test section area. Construction details are discussed for development of low-cost water tunnel for quantitative and qualitative fluid flow measurements. The water tunnel can also be used for educational purpose such as fluid dynamics class activity to provide quick access to visualization medium for better understanding of various turbulence motion learnt in class.

Time-Resolved Images of Laser-Induced Gas Ignition Using High-Speed Photographic and Spectroscopic Techniques

NASA Astrophysics Data System (ADS)

Chen, Ying-Ling; Lewis, J. W. L.; Parigger, C. G.

1997-11-01

Two-dimensional visualization of laser-induced spark ignition in atmospheric-pressure gases is reported. Laser-induced breakdown in air, O2 and combustible NH_3/O2 mixture was achieved using a 1064 nm, Nd:YAG laser of approximately 6 ns pulse width, focused at 10-mm above a 60-mm diameter flat-flame burner. An argon sheath-gas flow was used to stabilize the core flowfield. High-speed photographic techniques were applied to trace a complete sequence of kernel development of a single breakdown or ignition event. Thermochemical characteristics of the post-breakdown regime were analyzed by laser-induced fluorescence spectroscopy (LIFS). Spatial distribution of NH free radical observed by planar-LIF showed the contours of the developing flame-front. The corresponding NH temperature maps achieved by excitation LIFS and Boltzmann plot are also presented.

Loss reduction in axial-flow compressors through low-speed model testing

NASA Technical Reports Server (NTRS)

Wisler, D. C.

1984-01-01

A systematic procedure for reducing losses in axial-flow compressors is presented. In this procedure, a large, low-speed, aerodynamic model of a high-speed core compressor is designed and fabricated based on aerodynamic similarity principles. This model is then tested at low speed where high-loss regions associated with three-dimensional endwall boundary layers flow separation, leakage, and secondary flows can be located, detailed measurements made, and loss mechanisms determined with much greater accuracy and much lower cost and risk than is possible in small, high-speed compressors. Design modifications are made by using custom-tailored airfoils and vector diagrams, airfoil endbends, and modified wall geometries in the high-loss regions. The design improvements resulting in reduced loss or increased stall margin are then scaled to high speed. This paper describes the procedure and presents experimental results to show that in some cases endwall loss has been reduced by as much as 10 percent, flow separation has been reduced or eliminated, and stall margin has been substantially improved by using these techniques.

Experimental Investigation of Rotating Stall in a Research Multistage Axial Compressor

NASA Technical Reports Server (NTRS)

Lepicovsky, Jan; Braunscheidel, Edward P.; Welch, Gerard E.

2007-01-01

A collection of experimental data acquired in the NASA low-speed multistage axial compressor while operated in rotating stall is presented in this paper. The compressor was instrumented with high-response wall pressure modules and a static pressure disc probe for in-flow measurement, and a split-fiber probe for simultaneous measurements of velocity magnitude and flow direction. The data acquired to-date have indicated that a single fully developed stall cell rotates about the flow annulus at 50.6% of the rotor speed. The stall phenomenon is substantially periodic at a fixed frequency of 8.29 Hz. It was determined that the rotating stall cell extends throughout the entire compressor, primarily in the axial direction. Spanwise distributions of the instantaneous absolute flow angle, axial and tangential velocity components, and static pressure acquired behind the first rotor are presented in the form of contour plots to visualize different patterns in the outer (midspan to casing) and inner (hub to mid-span) flow annuli during rotating stall. In most of the cases observed, the rotating stall started with a single cell. On occasion, rotating stall started with two emerging stall cells. The root cause of the variable stall cell count is unknown, but is not attributed to operating procedures.

Lipid tubules Formed by Flow-Controlled Hydration

NASA Astrophysics Data System (ADS)

Yuan, Jing; Hirst, Linda S.

2007-03-01

Self-assembled cylindrical tubules from lipid molecules have attracted considerable attention because of their interesting supramolecular structures and technological applications. Schnur et al. [1] reported the formation of tubular microstructures from a series of diacetylenic phospholipids after liposomes were cooled through their chain melting transition. After that, several methods have been developed to fabricate such unique microstructures mainly by means of deforming preformed Giant unilamellar vesicles. Here we present a simple strategy to construct lipid microtubules through a flow-controlled lipid hydration. Fluorescent microscopy and Confocal Laser Microscopy were used to visualize the formation and the structure of the lipid tubules. Tubules were found to develop following the direction of the dynamic flow with highly parallel alignment. At high flow speeds, partial cross-linking of the lipid tubules was observed. To demonstrate the generality of this method, different types of phospholipids, such as Phosphatidic Acid (PA), Phosphatidylserine (PS), Phosphatidylethanolamine (PE), and Phosphatidylglycerol (PG) were investigated. [1] J.M. Schnur et al, Science, 264, 945 (1994).

Using Flow Charts to Visualize the Decision-Making Process in Space Weather Forecasting

NASA Astrophysics Data System (ADS)

Aung, M. T. Y.; Myat, T.; Zheng, Y.; Mays, M. L.; Ngwira, C.; Damas, M. C.

2016-12-01

Our society today relies heavily on technological systems such as satellites, navigation systems, power grids and aviation. These systems are very sensitive to space weather disturbances. When Earth-directed space weather driven by the Sun arrives at the Earth, it causes changes to the Earth's radiation environment and the magnetosphere. Strong disturbances in the magnetosphere of the Earth are responsible for geomagnetic storms that can last from hours to days depending on strength of storms. Geomagnetic storms can severely impact critical infrastructure on Earth, such as the electric power grid, and Solar Energetic Particles that can endanger life in outer space. How can we lessen these adverse effects? They can be lessened through the early warning signals sent by space weather forecasters before CME or high-speed stream arrives. A space weather forecaster's duty is to send predicted notifications to high-tech industries and NASA missions so that they could take extra measures for protection. NASA space weather forecasters make prediction decisions by following certain steps and processes from the time an event occurs at the sun all the way to the impact locations. However, there has never been a tool that helps these forecasters visualize the decision process until now. A flow chart is created to help forecasters visualize the decision process. This flow chart provides basic knowledge of space weather and can be used to train future space weather forecasters. It also helps to cut down the training period and increase consistency in forecasting. The flow chart is also a great reference for people who are already familiar with space weather.

[The Performance Analysis for Lighting Sources in Highway Tunnel Based on Visual Function].

PubMed

Yang, Yong; Han, Wen-yuan; Yan, Ming; Jiang, Hai-feng; Zhu, Li-wei

2015-10-01

Under the condition of mesopic vision, the spectral luminous efficiency function is shown as a series of curves. Its peak wavelength and intensity are affected by light spectrum, background brightness and other aspects. The impact of light source to lighting visibility could not be carried out via a single optical parametric characterization. The reaction time of visual cognition is regard as evaluating indexes in this experiment. Under the condition of different speed and luminous environment, testing visual cognition based on vision function method. The light sources include high pressure sodium, electrodeless fluorescent lamp and white LED with three kinds of color temperature (the range of color temperature is from 1 958 to 5 537 K). The background brightness value is used for basic section of highway tunnel illumination and general outdoor illumination, its range is between 1 and 5 cd x m(-)2. All values are in the scope of mesopic vision. Test results show that: under the same condition of speed and luminance, the reaction time of visual cognition that corresponding to high color temperature of light source is shorter than it corresponding to low color temperature; the reaction time corresponding to visual target in high speed is shorter than it in low speed. At the end moment, however, the visual angle of target in observer's visual field that corresponding to low speed was larger than it corresponding to high speed. Based on MOVE model, calculating the equivalent luminance of human mesopic vision, which is on condition of different emission spectrum and background brightness that formed by test lighting sources. Compared with photopic vision result, the standard deviation (CV) of time-reaction curve corresponding to equivalent brightness of mesopic vision is smaller. Under the condition of mesopic vision, the discrepancy between equivalent brightness of different lighting source and photopic vision, that is one of the main reasons for causing the discrepancy of visual recognition. The emission spectrum peak of GaN chip is approximate to the wave length peak of efficiency function in photopic vision. The lighting visual effect of write LED in high color temperature is better than it in low color temperature and electrodeless fluorescent lamp. The lighting visual effect of high pressure sodium is weak. Because of its peak value is around the Na+ characteristic spectra.

Computer-animated stimuli to measure motion sensitivity: constraints on signal design in the Jacky dragon

PubMed Central

Rieucau, Guillaume; Burke, Darren

2017-01-01

Abstract Identifying perceptual thresholds is critical for understanding the mechanisms that underlie signal evolution. Using computer-animated stimuli, we examined visual speed sensitivity in the Jacky dragon Amphibolurus muricatus, a species that makes extensive use of rapid motor patterns in social communication. First, focal lizards were tested in discrimination trials using random-dot kinematograms displaying combinations of speed, coherence, and direction. Second, we measured subject lizards’ ability to predict the appearance of a secondary reinforcer (1 of 3 different computer-generated animations of invertebrates: cricket, spider, and mite) based on the direction of movement of a field of drifting dots by following a set of behavioural responses (e.g., orienting response, latency to respond) to our virtual stimuli. We found an effect of both speed and coherence, as well as an interaction between these 2 factors on the perception of moving stimuli. Overall, our results showed that Jacky dragons have acute sensitivity to high speeds. We then employed an optic flow analysis to match the performance to ecologically relevant motion. Our results suggest that the Jacky dragon visual system may have been shaped to detect fast motion. This pre-existing sensitivity may have constrained the evolution of conspecific displays. In contrast, Jacky dragons may have difficulty in detecting the movement of ambush predators, such as snakes and of some invertebrate prey. Our study also demonstrates the potential of the computer-animated stimuli technique for conducting nonintrusive tests to explore motion range and sensitivity in a visually mediated species. PMID:29491965

Aperiodic pressure pulsation under non optimal hydraulic turbine regimes at low swirl number

NASA Astrophysics Data System (ADS)

Skripkin, S. G.; Tsoy, M. A.; Kuibin, P. A.; Shtork, S. I.

2017-09-01

Off-design operating conditions of hydraulic turbines is hindered by pressure fluctuations in the draft tube of the turbine. A precessing helical vortex rope develops, which imperils the mechanical structure and limits the operation flexibility of hydropower station. Understanding of the underlying instabilities of precessing vortex rope at low swirl number is incomplete. In this paper flow regimes with different residual swirl is analysed, particular attention is paid to the regime with a small swirl parameter. Study defines upper and low boundaries of regime where aperiodic pressure surge is observed. Flow field at the runner exit is investigated by Laser Doppler Velocimetry and high-speed visualizations, which are complemented draft tube wall pressure measurements.

Efficient LBM visual simulation on face-centered cubic lattices.

PubMed

Petkov, Kaloian; Qiu, Feng; Fan, Zhe; Kaufman, Arie E; Mueller, Klaus

2009-01-01

The Lattice Boltzmann method (LBM) for visual simulation of fluid flow generally employs cubic Cartesian (CC) lattices such as the D3Q13 and D3Q19 lattices for the particle transport. However, the CC lattices lead to suboptimal representation of the simulation space. We introduce the face-centered cubic (FCC) lattice, fD3Q13, for LBM simulations. Compared to the CC lattices, the fD3Q13 lattice creates a more isotropic sampling of the simulation domain and its single lattice speed (i.e., link length) simplifies the computations and data storage. Furthermore, the fD3Q13 lattice can be decomposed into two independent interleaved lattices, one of which can be discarded, which doubles the simulation speed. The resulting LBM simulation can be efficiently mapped to the GPU, further increasing the computational performance. We show the numerical advantages of the FCC lattice on channeled flow in 2D and the flow-past-a-sphere benchmark in 3D. In both cases, the comparison is against the corresponding CC lattices using the analytical solutions for the systems as well as velocity field visualizations. We also demonstrate the performance advantages of the fD3Q13 lattice for interactive simulation and rendering of hot smoke in an urban environment using thermal LBM.

Microfluidic volumetric flow determination using optical coherence tomography speckle: An autocorrelation approach

DOE Office of Scientific and Technical Information (OSTI.GOV)

De Pretto, Lucas R., E-mail: lucas.de.pretto@usp.br; Nogueira, Gesse E. C.; Freitas, Anderson Z.

2016-04-28

Functional modalities of Optical Coherence Tomography (OCT) based on speckle analysis are emerging in the literature. We propose a simple approach to the autocorrelation of OCT signal to enable volumetric flow rate differentiation, based on decorrelation time. Our results show that this technique could distinguish flows separated by 3 μl/min, limited by the acquisition speed of the system. We further perform a B-scan of gradient flow inside a microchannel, enabling the visualization of the drag effect on the walls.

Experimental investigation of forebody and wing leading-edge vortex interactions at high angles of attack

NASA Technical Reports Server (NTRS)

Erickson, G. E.; Gilbert, W. P.

1983-01-01

An experimental investigation was conducted to assess the vortex flow-field interactions on an advanced, twin-jet fighter aircraft configuration at high angles of attack. Flow-field surveys were conducted on a small-scale model in the Northrop 0.41 - by 0.60-meter water tunnel and, where appropriate, the qualitative observations were correlated with low-speed wind tunnel data trends obtained on a large-scale model of the advanced fighter in the NASA Langley Research Center 30- by 60-foot (9.1- by 18.3-meter) facility. Emphasis was placed on understanding the interactions of the forebody and LEX-wing vortical flows, defining the effects on rolling moment variation with sideslip, and identifying modifications to control or regulate the vortex interactions at high angles of attack. The water tunnel flow visualization results and wind tunnel data trend analysis revealed the potential for strong interactions between the forebody and LEX vortices at high angles of attack. In particular, the forebody flow development near the nose could be controlled by means of carefully-positioned radome strakes. The resultant strake-induced flow-field changes were amplified downstream by the more powerful LEX vortical motions with subsequent large effects on wing flow separation characteristics.

Sedentary behavior as a factor in determining lateral line contributions to rheotaxis.

PubMed

Bak-Coleman, Joseph; Coombs, Sheryl

2014-07-01

Rheotaxis is a robust, multisensory behavior with many potential benefits for fish and other aquatic animals. Visual (optic flow) cues appear to be sufficient for rheotaxis, but other sensory cues can clearly compensate for the loss of vision. The role of various non-visual sensory systems, in particular the flow-sensing lateral line, is poorly understood, largely because of widely varying methods and sensory conditions for studying rheotaxis. Here, we examine how sedentary behavior under visually deprived conditions affects the relative importance of lateral line cues in two species: one that is normally sedentary (the three-lined corydoras, Corydoras trilineatus) and one that normally swims continuously along the substrate (the blind cavefish, Astyanax mexicanus). No effect of lateral line disruption on rheotactic performance was found in blind cavefish, which were significantly more mobile than three-lined corydoras. By contrast, rheotaxis was significantly impaired at low, but not high, flow speeds in lateral-line-disabled corydoras. In addition, lateral-line-enabled corydoras were characterized by decreased mobility and increased rheotactic performance relative to lateral-line-disabled fish. Taken together, these results suggest that sedentary behavior is an important factor in promoting reliance on lateral line cues. © 2014. Published by The Company of Biologists Ltd.

Homage to Bob Brodkey at 85: ejections, sweeps and the genesis and extensions of quadrant analysis

NASA Astrophysics Data System (ADS)

Wallace, James

2013-11-01

Almost 50 years ago Bob Brodkey and his student, Corino, conceived and carried out a visualization experiment for the very near wall region of a turbulent pipe flow (JFM 37) that, together with the turbulent boundary layer visualization of Kline et al. (JFM 30), excited the turbulence community. Using a high speed movie camera mounted on a lathe bed that recorded magnified images in a moving frame of reference, they observed the motions of small particles in the sub- and buffer-layers. Surprisingly, these motion were not nearly so locally random as was the general view of turbulence at the time. Rather, connected regions of the near wall flow decelerated and then erupted away from the wall in what they called ``ejections.'' These decelerated motions were followed by larger scale connected motions toward the wall from above that they called ``sweeps.'' Brodkey and Corino estimated that ejections accounted for 70 % the Reynolds shear stress at Red = 20 , 000 while only occurring about 18 % of the time. Wallace et al. (JFM 54) attempted to quantify these visual observations by conceiving of and carrying out a quadrant analyisis in a turbulent oil channel flow. This paper will trace this history and describe the expanding use of these ideas in turbulence research today.

Improved Visualization of Glaucomatous Retinal Damage Using High-speed Ultrahigh-Resolution Optical Coherence Tomography

PubMed Central

Mumcuoglu, Tarkan; Wollstein, Gadi; Wojtkowski, Maciej; Kagemann, Larry; Ishikawa, Hiroshi; Gabriele, Michelle L.; Srinivasan, Vivek; Fujimoto, James G.; Duker, Jay S.; Schuman, Joel S.

2009-01-01

Purpose To test if improving optical coherence tomography (OCT) resolution and scanning speed improves the visualization of glaucomatous structural changes as compared with conventional OCT. Design Prospective observational case series. Participants Healthy and glaucomatous subjects in various stages of disease. Methods Subjects were scanned at a single visit with commercially available OCT (StratusOCT) and high-speed ultrahigh-resolution (hsUHR) OCT. The prototype hsUHR OCT had an axial resolution of 3.4 μm (3 times higher than StratusOCT), with an A-scan rate of 24 000 hertz (60 times faster than StratusOCT). The fast scanning rate allowed the acquisition of novel scanning patterns such as raster scanning, which provided dense coverage of the retina and optic nerve head. Main Outcome Measures Discrimination of retinal tissue layers and detailed visualization of retinal structures. Results High-speed UHR OCT provided a marked improvement in tissue visualization as compared with StratusOCT. This allowed the identification of numerous retinal layers, including the ganglion cell layer, which is specifically prone to glaucomatous damage. Fast scanning and the enhanced A-scan registration properties of hsUHR OCT provided maps of the macula and optic nerve head with unprecedented detail, including en face OCT fundus images and retinal nerve fiber layer thickness maps. Conclusion High-speed UHR OCT improves visualization of the tissues relevant to the detection and management of glaucoma. PMID:17884170

Flow visualization of mast-mounted-sight/main rotor aerodynamic interactions

NASA Technical Reports Server (NTRS)

Ghee, Terence A.; Kelley, Henry L.

1993-01-01

Flow visualization tests were conducted on a 27 percent-scale AH-64 attack helicopter model fitted with various mast-mounted-sight configurations in an attempt to identify the cause of adverse vibration encountered during full-scale flight tests of an Apache/Longbow configuration. The tests were conducted at the NASA Langley Research Center in the 14- by 22-Foot Subsonic Tunnel. A symmetric and an asymmetric mast-mounted-sight oriented at several skew angles were tested at forward and rearward flight speeds of 30 and 45 knots. A laser light sheet seeded with vaporized propylene glycol was used to visualize the wake of the sight in planes parallel and perpendicular to the freestream flow. Analysis of the flow visualization data identified the frequency of the wake shed from the sight, the angle-of-attack at the sight, and the location where the sight wake crossed the rotor plane. Differences in wake structure were observed between the various sight configurations and slew angles. Postulations into the cause of the adverse vibration found in flight test are given along with considerations for future tests.

Vortex formation with a snapping shrimp claw.

PubMed

Hess, David; Brücker, Christoph; Hegner, Franziska; Balmert, Alexander; Bleckmann, Horst

2013-01-01

Snapping shrimp use one oversized claw to generate a cavitating high speed water jet for hunting, defence and communication. This work is an experimental investigation about the jet generation. Snapping shrimp (Alpheus-bellulus) were investigated by using an enlarged transparent model reproducing the closure of the snapper claw. Flow inside the model was studied using both High-Speed Particle Image Velocimetry (HS-PIV) and flow visualization. During claw closure a channel-like cavity was formed between the plunger and the socket featuring a nozzle-type contour at the orifice. Closing the mechanism led to the formation of a leading vortex ring with a dimensionless formation number of approximate ΔT*≈4. This indicates that the claw might work at maximum efficiency, i.e. maximum vortex strength was achieved by a minimum of fluid volume ejected. The subsequent vortex cavitation with the formation of an axial reentrant jet is a reasonable explanation for the large penetration depth of the water jet. That snapping shrimp can reach with their claw-induced flow. Within such a cavitation process, an axial reentrant jet is generated in the hollow cylindrical core of the cavitated vortex that pushes the front further downstream and whose length can exceed the initial jet penetration depth by several times.

Flow Visualization of Aircraft in Flight by Means of Background Oriented Schlieren Using Celestial Objects

NASA Technical Reports Server (NTRS)

Hill, Michael A.; Haering, Edward A., Jr.

2017-01-01

The Background Oriented Schlieren using Celestial Objects series of flights was undertaken in the spring of 2016 at National Aeronautics and Space Administration Armstrong Flight Research Center to further develop and improve a flow visualization technique which can be performed from the ground upon flying aircraft. Improved hardware and imaging techniques from previous schlieren tests were investigated. A United States Air Force T-38C and NASA B200 King Air aircraft were imaged eclipsing the sun at ranges varying from 2 to 6 nautical miles, at subsonic and supersonic speeds.

Stereoscopic Imaging in Hypersonics Boundary Layers using Planar Laser-Induced Fluorescence

NASA Technical Reports Server (NTRS)

Danehy, Paul M.; Bathel, Brett; Inman, Jennifer A.; Alderfer, David W.; Jones, Stephen B.

2008-01-01

Stereoscopic time-resolved visualization of three-dimensional structures in a hypersonic flow has been performed for the first time. Nitric Oxide (NO) was seeded into hypersonic boundary layer flows that were designed to transition from laminar to turbulent. A thick laser sheet illuminated and excited the NO, causing spatially-varying fluorescence. Two cameras in a stereoscopic configuration were used to image the fluorescence. The images were processed in a computer visualization environment to provide stereoscopic image pairs. Two methods were used to display these image pairs: a cross-eyed viewing method which can be viewed by naked eyes, and red/blue anaglyphs, which require viewing through red/blue glasses. The images visualized three-dimensional information that would be lost if conventional planar laser-induced fluorescence imaging had been used. Two model configurations were studied in NASA Langley Research Center's 31-Inch Mach 10 Air Wind tunnel. One model was a 10 degree half-angle wedge containing a small protuberance to force the flow to transition. The other model was a 1/3-scale, truncated Hyper-X forebody model with blowing through a series of holes to force the boundary layer flow to transition to turbulence. In the former case, low flowrates of pure NO seeded and marked the boundary layer fluid. In the latter, a trace concentration of NO was seeded into the injected N2 gas. The three-dimensional visualizations have an effective time resolution of about 500 ns, which is fast enough to freeze this hypersonic flow. The 512x512 resolution of the resulting images is much higher than high-speed laser-sheet scanning systems with similar time response, which typically measure 10-20 planes.

Wind Tunnel Investigation of Passive Vortex Control and Vortex-Tail Interactions on a Slender Wing at Subsonic and Transonic Speeds

NASA Technical Reports Server (NTRS)

Erickson, Gary E.

2013-01-01

A wind tunnel experiment was conducted in the NASA Langley 8-Foot Transonic Pressure Tunnel to determine the effects of passive porosity on vortex flow interactions about a slender wing configuration at subsonic and transonic speeds. Flow-through porosity was applied in several arrangements to a leading-edge extension, or LEX, mounted to a 65-degree cropped delta wing as a longitudinal instability mitigation technique. Test data were obtained with LEX on and off in the presence of a centerline vertical tail and twin, wing-mounted vertical fins to quantify the sensitivity of the aerodynamics to tail placement and orientation. A close-coupled canard was tested as an alternative to the LEX as a passive flow control device. Wing upper surface static pressure distributions and six-component forces and moments were obtained at Mach numbers of 0.50, 0.85, and 1.20, unit Reynolds number of 2.5 million, angles of attack up to approximately 30 degrees, and angles of sideslip to +/-8 degrees. The off-surface flow field was visualized in cross planes on selected configurations using a laser vapor screen flow visualization technique. Tunnel-to-tunnel data comparisons and a Reynolds number sensitivity assessment were also performed. 15.

Development of High-speed Visualization System of Hypocenter Data Using CUDA-based GPU computing

NASA Astrophysics Data System (ADS)

Kumagai, T.; Okubo, K.; Uchida, N.; Matsuzawa, T.; Kawada, N.; Takeuchi, N.

2014-12-01

After the Great East Japan Earthquake on March 11, 2011, intelligent visualization of seismic information is becoming important to understand the earthquake phenomena. On the other hand, to date, the quantity of seismic data becomes enormous as a progress of high accuracy observation network; we need to treat many parameters (e.g., positional information, origin time, magnitude, etc.) to efficiently display the seismic information. Therefore, high-speed processing of data and image information is necessary to handle enormous amounts of seismic data. Recently, GPU (Graphic Processing Unit) is used as an acceleration tool for data processing and calculation in various study fields. This movement is called GPGPU (General Purpose computing on GPUs). In the last few years the performance of GPU keeps on improving rapidly. GPU computing gives us the high-performance computing environment at a lower cost than before. Moreover, use of GPU has an advantage of visualization of processed data, because GPU is originally architecture for graphics processing. In the GPU computing, the processed data is always stored in the video memory. Therefore, we can directly write drawing information to the VRAM on the video card by combining CUDA and the graphics API. In this study, we employ CUDA and OpenGL and/or DirectX to realize full-GPU implementation. This method makes it possible to write drawing information to the VRAM on the video card without PCIe bus data transfer: It enables the high-speed processing of seismic data. The present study examines the GPU computing-based high-speed visualization and the feasibility for high-speed visualization system of hypocenter data.

In-flight imaging of transverse gas jets injected into transonic and supersonic crossflows: Design and development. M.S. Thesis, Mar. 1993

NASA Technical Reports Server (NTRS)

Wang, Kon-Sheng Charles

1994-01-01

The design and development of an airborne flight-test experiment to study nonreacting gas jets injected transversely into transonic and supersonic crossflows is presented. Free-stream/crossflow Mach numbers range from 0.8 to 2.0. Planar laser-induced fluorescence (PLIF) of an iodine-seeded nitrogen jet is used to visualize the jet flow. Time-dependent images are obtained with a high-speed intensified video camera synchronized to the laser pulse rate. The entire experimental assembly is configured compactly inside a unique flight-test-fixture (FTF) mounted under the fuselage of the F-104G research aircraft, which serves as a 'flying wind tunnel' at NASA Dryden Flight Research Center. The aircraft is flown at predetermined speeds and altitudes to permit a perfectly expanded (or slightly underexpanded) gas jet to form just outside the FTF at each free-stream Mach number. Recorded gas jet images are then digitized to allow analysis of jet trajectory, spreading, and mixing characteristics. Comparisons will be made with analytical and numerical predictions. This study shows the viability of applying highly sophisticated groundbased flow diagnostic techniques to flight-test vehicle platforms that can achieve a wide range of thermo/fluid dynamic conditions. Realistic flow environments, high enthalpies, unconstrained flowfields, and moderate operating costs are also realized, in contrast to traditional wind-tunnel testing.

Control of low-speed turbulent separated flow over a backward-facing ramp. Ph.D. Thesis - Old Dominion Univ.

NASA Technical Reports Server (NTRS)

Lin, John C.

1992-01-01

The relative performance and flow phenomena associated with several devices for controlling turbulent separated flow were investigated at low speeds. Relative performance of the devices was examined for flow over a curved, backward-facing ramp in a wind tunnel, and the flow phenomena were examined in a water tunnel using dye-flow visualization. Surface static pressure measurements and oil-flow visualization results from the wind tunnel tests indicated that transverse grooves, longitudinal grooves, submerged vortex generators, vortex generator jets (VGJ's), Viets' fluidic flappers, elongated arches at positive angle of attack, and large-eddy breakup devices (LEBU's) at positive angle of attack placed near the baseline separation location reduce flow separation and increase pressure recovery. Spanwise cylinders reduce flow separation but decrease pressure recovery downstream. Riblets, passive porous surfaces, swept grooves, Helmholtz resonators, and arches and LEBU's with angle of attack less than or = 0 degrees had no significant effect in reducing the extent of the separation region. Wall-cooling computations indicated that separation delay on a partially-cooled ramp is nearly the same as on a fully-cooled ramp, while minimizing the frictional drag increase associated with the wall cooling process. Dry-flow visualization tests in the water tunnel indicated that wishbone vortex generators in the forward orientation shed horseshoe vortices; wishbone vortex generators oriented in the reverse direction and doublet vortex generators shed streamwise counterrotating vortices; a spanewise cylinder located near the wall and LEBU's at angle of attack = -10 degrees produced eddies or transverse vortices which rotated with the same sign as the mean vorticity in a turbulent boundary layer; and the most effective VGJ's produced streamwise co-rotating vortices. Comparative wind-tunnel test results indicated that transferring momentum from the outer region of a turbulent boundary layer through the action of embedded streamwise vortices is more effective than by transverse vortices for the separation control application studied herein.

Burst Speed of Wild Fishes under High-Velocity Flow Conditions Using Stamina Tunnel with Natural Guidance System in River

NASA Astrophysics Data System (ADS)

Izumi, Mattashi; Yamamoto, Yasuyuki; Yataya, Kenichi; Kamiyama, Kohhei

Swimming experiments were conducted on wild fishes in a natural guidance system stamina tunnel (cylindrical pipe) installed in a fishway of a local river under high-velocity flow conditions (tunnel flow velocity : 211 to 279 cm·s-1). In this study, the swimming characteristics of fishes were observed. The results show that (1) the swimming speeds of Tribolodon hakonensis (Japanese dace), Phoxinus lagowshi steindachneri (Japanese fat-minnow), Plecoglossus altivelis (Ayu), and Zacco platypus (Pale chub) were in proportion to their body length under identical water flow velocity conditions; (2) the maximum burst speed of Japanese dace and Japanese fat-minnow (measuring 4 to 6 cm in length) was 262 to 319 cm·s-1 under high flow velocity conditions (225 to 230 cm·s-1), while the maximum burst speed of Ayu and Pale chub (measuring 5 cm to 12 cm in length) was 308 to 355 cm·s-1 under high flow velocity conditions (264 to 273 cm·s-1) ; (3) the 50cm-maximum swimming speed of swimming fishes was 1.07 times faster than the pipe-swimming speed; (4) the faster the flow velocity, the shorter the swimming distance became.

A mesh regeneration method using quadrilateral and triangular elements for compressible flows

NASA Technical Reports Server (NTRS)

Vemaganti, G. R.; Thornton, E. A.

1989-01-01

An adaptive remeshing method using both triangular and quadrilateral elements suitable for high-speed viscous flows is presented. For inviscid flows, the method generates completely unstructured meshes. For viscous flows, structured meshes are generated for boundary layers, and unstructured meshes are generated for inviscid flow regions. Examples of inviscid and viscous adaptations for high-speed flows are presented.

Computer capillaroscopy as a new cardiological diagnostics method

NASA Astrophysics Data System (ADS)

Gurfinkel, Youri I.; Korol, Oleg A.; Kufal, George E.

1998-04-01

The blood flow in capillary vessels plays an important role in sustaining the vital activity of the human organism. The computerized capillaroscope is used for the investigations of nailfold (eponychium) capillary blood flow. An important advantage of the instrument is the possibility of performing non-invasive investigations, i.e., without damage to skin or vessels and causing no pain or unpleasant sensations. The high-class equipment and software allow direct observation of capillary blood flow dynamics on a computer screen at a 700 - 1300 times magnification. For the first time in the clinical practice, it has become possible to precisely measure the speed of capillary blood flow, as well as the frequency of aggregate formation (glued together in clots of blood particles). In addition, provision is made for automatic measurement of capillary size and wall thickness and automatic recording of blood aggregate images for further visual study, documentation, and electronic database management.

The Role of Visual Processing Speed in Reading Speed Development

PubMed Central

Lobier, Muriel; Dubois, Matthieu; Valdois, Sylviane

2013-01-01

A steady increase in reading speed is the hallmark of normal reading acquisition. However, little is known of the influence of visual attention capacity on children's reading speed. The number of distinct visual elements that can be simultaneously processed at a glance (dubbed the visual attention span), predicts single-word reading speed in both normal reading and dyslexic children. However, the exact processes that account for the relationship between the visual attention span and reading speed remain to be specified. We used the Theory of Visual Attention to estimate visual processing speed and visual short-term memory capacity from a multiple letter report task in eight and nine year old children. The visual attention span and text reading speed were also assessed. Results showed that visual processing speed and visual short term memory capacity predicted the visual attention span. Furthermore, visual processing speed predicted reading speed, but visual short term memory capacity did not. Finally, the visual attention span mediated the effect of visual processing speed on reading speed. These results suggest that visual attention capacity could constrain reading speed in elementary school children. PMID:23593117

The role of visual processing speed in reading speed development.

PubMed

Lobier, Muriel; Dubois, Matthieu; Valdois, Sylviane

2013-01-01

A steady increase in reading speed is the hallmark of normal reading acquisition. However, little is known of the influence of visual attention capacity on children's reading speed. The number of distinct visual elements that can be simultaneously processed at a glance (dubbed the visual attention span), predicts single-word reading speed in both normal reading and dyslexic children. However, the exact processes that account for the relationship between the visual attention span and reading speed remain to be specified. We used the Theory of Visual Attention to estimate visual processing speed and visual short-term memory capacity from a multiple letter report task in eight and nine year old children. The visual attention span and text reading speed were also assessed. Results showed that visual processing speed and visual short term memory capacity predicted the visual attention span. Furthermore, visual processing speed predicted reading speed, but visual short term memory capacity did not. Finally, the visual attention span mediated the effect of visual processing speed on reading speed. These results suggest that visual attention capacity could constrain reading speed in elementary school children.

Comparing a Fischer-Tropsch Alternate Fuel to JP-8 and Their 50-50 Blend: Flow and Flame Visualization Results

NASA Technical Reports Server (NTRS)

Hicks, Yolanda R.; Tacina, M.

2013-01-01

Combustion performance of a Fischer-Tropsch (FT) jet fuel manufactured by Sasol was compared to JP-8 and a 50-50 blend of the two fuels, using the NASA/Woodward 9 point Lean Direct Injector (LDI) in its baseline configuration. The baseline LDI configuration uses 60deg axial air-swirlers, whose vanes generate clockwise swirl, in the streamwise sense. For all cases, the fuel-air equivalence ratio was 0.455, and the combustor inlet pressure and pressure drop were 10-bar and 4 percent. The three inlet temperatures used were 828, 728, and 617 K. The objectives of this experiment were to visually compare JP-8 flames with FT flames for gross features. Specifically, we sought to ascertain in a simple way visible luminosity, sooting, and primary flame length of the FT compared to a standard JP grade fuel. We used color video imaging and high-speed imaging to achieve these goals. The flame color provided a way to qualitatively compare soot formation. The length of the luminous signal measured using the high speed camera allowed an assessment of primary flame length. It was determined that the shortest flames resulted from the FT fuel.

Experimental and computational investigation of the NASA Low-Speed Centrifugal Compressor flow field

NASA Technical Reports Server (NTRS)

Hathaway, M. D.; Chriss, R. M.; Wood, J. R.; Strazisar, A. J.

1992-01-01

An experimental and computational investigation of the NASA Low-Speed Centrifugal Compressor (LSCC) flow field has been conducted using laser anemometry and Dawes' 3D viscous code. The experimental configuration consists of a backswept impeller followed by a vaneless diffuser. Measurements of the three-dimensional velocity field were acquired at several measurement planes through the compressor. The measurements describe both the throughflow and secondary velocity field along each measurement plane. In several cases the measurements provide details of the flow within the blade boundary layers. Insight into the complex flow physics within centrifugal compressors is provided by the computational analysis, and assessment of the CFD predictions is provided by comparison with the measurements. Five-hole probe and hot-wire surveys at the inlet and exit to the rotor as well as surface flow visualization along the impeller blade surfaces provide independent confirmation of the laser measurement technique.

High speed video shooting with continuous-wave laser illumination in laboratory modeling of wind - wave interaction

NASA Astrophysics Data System (ADS)

Kandaurov, Alexander; Troitskaya, Yuliya; Caulliez, Guillemette; Sergeev, Daniil; Vdovin, Maxim

2014-05-01

Three examples of usage of high-speed video filming in investigation of wind-wave interaction in laboratory conditions is described. Experiments were carried out at the Wind - wave stratified flume of IAP RAS (length 10 m, cross section of air channel 0.4 x 0.4 m, wind velocity up to 24 m/s) and at the Large Air-Sea Interaction Facility (LASIF) - MIO/Luminy (length 40 m, cross section of air channel 3.2 x 1.6 m, wind velocity up to 10 m/s). A combination of PIV-measurements, optical measurements of water surface form and wave gages were used for detailed investigation of the characteristics of the wind flow over the water surface. The modified PIV-method is based on the use of continuous-wave (CW) laser illumination of the airflow seeded by particles and high-speed video. During the experiments on the Wind - wave stratified flume of IAP RAS Green (532 nm) CW laser with 1.5 Wt output power was used as a source for light sheet. High speed digital camera Videosprint (VS-Fast) was used for taking visualized air flow images with the frame rate 2000 Hz. Velocity air flow field was retrieved by PIV images processing with adaptive cross-correlation method on the curvilinear grid following surface wave profile. The mean wind velocity profiles were retrieved using conditional in phase averaging like in [1]. In the experiments on the LASIF more powerful Argon laser (4 Wt, CW) was used as well as high-speed camera with higher sensitivity and resolution: Optronics Camrecord CR3000x2, frame rate 3571 Hz, frame size 259×1696 px. In both series of experiments spherical 0.02 mm polyamide particles with inertial time 7 ms were used for seeding airflow. New particle seeding system based on utilization of air pressure is capable of injecting 2 g of particles per second for 1.3 - 2.4 s without flow disturbance. Used in LASIF this system provided high particle density on PIV-images. In combination with high-resolution camera it allowed us to obtain momentum fluxes directly from measured air velocity fluctuations. This data was then compared to values retrieved from wind speed profiles [2]. Visualization of water surface structure and droplets under strong wind conditions was carried out at the Wind - wave stratified flume of IAP RAS with high-speed camera NAC Memrecam HX-3 having a record-breaking performance at the moment. Shooting was performed at frame rates over 4500 Hz in 1080p resolution (1920 x 1080 px). Experimental study of droplets under strong winds has discovered a "bag breakup" droplet-production mechanism (observed previously in technical devices for liquid disintegration [3]). The investigation on this mechanism in the laboratory can improve the parameterization of heat fluxes in the models of hurricanes and intense sea storms. This work was supported by RFBR grants (project code 13-05-00865, 13-05-12093, 12-05-01064, 14-08-31740, 14-05-31415), President Grant for young scientists MK-3550.2014.5 and grant of the Government of the Russian Federation designed to support scientific research project implemented under the supervision of leading scientists at Russian institutions of higher learning (project code 11.G34.31.0048). References 1. Troitskaya Yu., D. Sergeev, O. Ermakova, G. Balandina (2011), Statistical Parameters of the Air Turbulent Boundary Layer over Steep Water Waves Measured by the PIV Technique, J. Phys. Oceanogr., 41, 1421-1454 2. Troitskaya, Y. I., D. A. Sergeev, A. A. Kandaurov, G. A. Baidakov, M. A. Vdovin, and V. I. Kazakov "Laboratory and theoretical modeling of air-sea momentum transfer under severe wind conditions" J. Geophys. Res., 117, C00J21, 2012. 3. Villermaux, E. (2007), Fragmentation, Ann. Review Fluid Mech., 39,419-446, doi:10.1146/annurev.fluid.39.050905.110214.

Phasic alertness cues modulate visual processing speed in healthy aging.

PubMed

Haupt, Marleen; Sorg, Christian; Napiórkowski, Natan; Finke, Kathrin

2018-05-31

Warning signals temporarily increase the rate of visual information in younger participants and thus optimize perception in critical situations. It is unclear whether such important preparatory processes are preserved in healthy aging. We parametrically assessed the effects of auditory alertness cues on visual processing speed and their time course using a whole report paradigm based on the computational Theory of Visual Attention. We replicated prior findings of significant alerting benefits in younger adults. In conditions with short cue-target onset asynchronies, this effect was baseline-dependent. As younger participants with high baseline speed did not show a profit, an inverted U-shaped function of phasic alerting and visual processing speed was implied. Older adults also showed a significant cue-induced benefit. Bayesian analyses indicated that the cueing benefit on visual processing speed was comparably strong across age groups. Our results indicate that in aging individuals, comparable to younger ones, perception is active and increased expectancy of the appearance of a relevant stimulus can increase the rate of visual information uptake. Copyright © 2018 Elsevier Inc. All rights reserved.

Flow speed of the ablation vapors generated during laser drilling of CFRP with a continuous-wave laser beam

NASA Astrophysics Data System (ADS)

Faas, S.; Freitag, C.; Boley, S.; Berger, P.; Weber, R.; Graf, T.

2017-03-01

The hot plume of ablation products generated during the laser drilling process of carbon fiber reinforced plastics (CFRP) with a continuous-wave laser beam was analyzed by means of high-speed imaging. The formation of compression shocks was observed within the flow of the evaporated material, which is an indication of flow speeds well above the local speed of sound. The flow speed of the hot ablation products can be estimated by analyzing the position of these compression shocks. We investigated the temporal evolution of the flow speed during the drilling process and the influence of the average laser power on the flow speed. The flow speed increases with increasing average laser powers. The moment of drilling through the material changes the conditions for the drilling process and was confirmed to influence the flow speed of the ablated material. Compression shocks can also be observed during laser cutting of CFRP with a moving laser beam.

First-Person Visualizations of the Special and General Theory of Relativity

ERIC Educational Resources Information Center

Kraus, U.

2008-01-01

Visualizations that adopt a first-person point of view allow observation and, in the case of interactive simulations, experimentation with relativistic scenes. This paper gives examples of three types of first-person visualizations: watching objects that move at nearly the speed of light, being a high-speed observer looking at a static environment…

Numerical Simulation of High-Speed Turbulent Reacting Flows

NASA Technical Reports Server (NTRS)

Givi, P.; Taulbee, D. B.; Madnia, C. K.; Jaberi, F. A.; Colucci, P. J.; Gicquel, L. Y. M.; Adumitroaie, V.; James, S.

1999-01-01

The objectives of this research are: (1) to develop and implement a new methodology for large eddy simulation of (LES) of high-speed reacting turbulent flows. (2) To develop algebraic turbulence closures for statistical description of chemically reacting turbulent flows.

The sensory basis of rheotaxis in turbulent flow

NASA Astrophysics Data System (ADS)

Elder, John P.

Rheotaxis is a robust, multisensory behavior with many potential benefits for fish and other aquatic animals, yet the influence of different fluvial conditions on rheotactic performance and its sensory basis is still poorly understood. Here, we examine the role that vision and the lateral line play in the rheotactic behavior of a stream-dwelling species (Mexican tetra, Astyanax mexicanus) under both rectilinear and turbulent flow conditions. Turbulence enhanced overall rheotactic strength and lowered the flow speed at which rheotaxis was initiated; this effect did not depend on the availability of either visual or lateral line information. Compared to fish without access to visual information, fish with access to visual information exhibited increased levels of positional stability and as a result, increased levels of rheotactic accuracy. No disruption in rheotactic performance was found when the lateral line was disabled, suggesting that this sensory system is not necessary for either rheotaxis or turbulence detection under the conditions of this study.

Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows

NASA Technical Reports Server (NTRS)

Givi, Peyman; Madnia, Cyrus K.; Steinberger, Craig J.

1990-01-01

This research is involved with the implementation of advanced computational schemes based on large eddy simulations (LES) and direct numerical simulations (DNS) to study the phenomenon of mixing and its coupling with chemical reactions in compressible turbulent flows. In the efforts related to LES, a research program to extend the present capabilities of this method was initiated for the treatment of chemically reacting flows. In the DNS efforts, the focus is on detailed investigations of the effects of compressibility, heat release, and non-equilibrium kinetics modelings in high speed reacting flows. Emphasis was on the simulations of simple flows, namely homogeneous compressible flows, and temporally developing high speed mixing layers.

Ultrahigh-Speed Optical Coherence Tomography for Three-Dimensional and En Face Imaging of the Retina and Optic Nerve Head

PubMed Central

Srinivasan, Vivek J.; Adler, Desmond C.; Chen, Yueli; Gorczynska, Iwona; Huber, Robert; Duker, Jay S.; Schuman, Joel S.; Fujimoto, James G.

2009-01-01

Purpose To demonstrate ultrahigh-speed optical coherence tomography (OCT) imaging of the retina and optic nerve head at 249,000 axial scans per second and a wavelength of 1060 nm. To investigate methods for visualization of the retina, choroid, and optic nerve using high-density sampling enabled by improved imaging speed. Methods A swept-source OCT retinal imaging system operating at a speed of 249,000 axial scans per second was developed. Imaging of the retina, choroid, and optic nerve were performed. Display methods such as speckle reduction, slicing along arbitrary planes, en face visualization of reflectance from specific retinal layers, and image compounding were investigated. Results High-definition and three-dimensional (3D) imaging of the normal retina and optic nerve head were performed. Increased light penetration at 1060 nm enabled improved visualization of the choroid, lamina cribrosa, and sclera. OCT fundus images and 3D visualizations were generated with higher pixel density and less motion artifacts than standard spectral/Fourier domain OCT. En face images enabled visualization of the porous structure of the lamina cribrosa, nerve fiber layer, choroid, photoreceptors, RPE, and capillaries of the inner retina. Conclusions Ultrahigh-speed OCT imaging of the retina and optic nerve head at 249,000 axial scans per second is possible. The improvement of ∼5 to 10× in imaging speed over commercial spectral/Fourier domain OCT technology enables higher density raster scan protocols and improved performance of en face visualization methods. The combination of the longer wavelength and ultrahigh imaging speed enables excellent visualization of the choroid, sclera, and lamina cribrosa. PMID:18658089

Enhancement of Condensation Heat Transfer by Counter-Corrent Wavy Flow in a Vertical Tube

NASA Astrophysics Data System (ADS)

Teranishi, Tsunenobu; Ozawa, Takanori; Takimoto, Akira

As a basic research for the development of a high-performance and environment-friendly thermal energy recovery system, detailed experiments have been conducted to investigate the mechanism of the enhancement of condensation heat transfer by the counter-current moist air flow in a vertical tube. From the results of visual observation of the phenomena by using a high-speed video recorder and the measurement of condensate rate respectively from an upper and a bottom end of a cooled tube, in which various humidity vapor of air and water flowed upward or downward, the dynamic behavior of liquid film condensed on cooled surface and moist air flow was classified into four distinctive patterns in quality and quantity. Further, the effect of the scale and the operating condition such as the diameter and the length of tube, the vapor concentration and the moist air temperature, on the condensation rate of counter-current wavy flow was clarified in relation to the pattern and condition of occurrence of the wavy flow of liquid film and flooding due to the shear forces between the interface of liquid and moist air flow.

Influence of Additional Leading-Edge Surface Roughness on Performances in Highly Loaded Compressor Cascade

NASA Astrophysics Data System (ADS)

Chen, Shaowen; Xu, Hao; Sun, Shijun; Zhang, Longxin; Wang, Songtao

2015-05-01

Experimental research has been carried out at low speed to investigate the effect of additional leading-edge surface roughness on a highly-loaded axial compressor cascade. A 5-hole aerodynamic probe has been traversed across one pitch to obtain the distribution of total pressure loss coefficient, secondary flow vector, flow angles and other aerodynamic parameters at the exit section. Meanwhile, ink-trace flow visualization has been used to measure the flow fields on the walls of cascades and a detailed topology structure of the flow on the walls has been obtained. Aerodynamic parameters and flow characteristics are compared by arranging different levels of roughness on various parts of the leading edge. The results show that adding surface roughness at the leading edge and on the suction side obviously influences cascade performance. Aggravated 3-D flow separation significantly increases the loss in cascades, and the loss increases till 60% when the level of emery paper is 80 mm. Even there is the potential to improve cascade performance in local area of cascade passage. The influence of the length of surface roughness on cascade performance is not always adverse, and which depends on the position of surface roughness.

New test techniques and analytical procedures for understanding the behavior of advanced propellers

NASA Technical Reports Server (NTRS)

Stefko, G. L.; Bober, L. J.; Neumann, H. E.

1983-01-01

Analytical procedures and experimental techniques were developed to improve the capability to design advanced high speed propellers. Some results from the propeller lifting line and lifting surface aerodynamic analysis codes are compared with propeller force data, probe data and laser velocimeter data. In general, the code comparisons with data indicate good qualitative agreement. A rotating propeller force balance demonstrated good accuracy and reduced test time by 50 percent. Results from three propeller flow visualization techniques are shown which illustrate some of the physical phenomena occurring on these propellers.

Low-speed aerodynamic characteristics of a generic forward-swept-wing aircraft

NASA Technical Reports Server (NTRS)

Ross, J. C.; Matarazzo, A. D.

1982-01-01

Low-speed wind-tunnel tests were performed on a generic forward-swept-wing aircraft model in the 7- by 10-Foot Wind Tunnel (No. 2) at Ames Research Center. The effects of various configurational changes and control-surface deflections on the performance of the model were measured. Six-component force measurements were augmented by flow-visualization photographs, using both surface oil-flow and tufts. It was found that the tendency toward premature root separation on the forward-swept wing could be reduced by use of either canards or leading-edge wing strakes and that differential canard deflections can be used to produce a direct side-force control.

Microfluidic Imaging Flow Cytometry by Asymmetric-detection Time-stretch Optical Microscopy (ATOM).

PubMed

Tang, Anson H L; Lai, Queenie T K; Chung, Bob M F; Lee, Kelvin C M; Mok, Aaron T Y; Yip, G K; Shum, Anderson H C; Wong, Kenneth K Y; Tsia, Kevin K

2017-06-28

Scaling the number of measurable parameters, which allows for multidimensional data analysis and thus higher-confidence statistical results, has been the main trend in the advanced development of flow cytometry. Notably, adding high-resolution imaging capabilities allows for the complex morphological analysis of cellular/sub-cellular structures. This is not possible with standard flow cytometers. However, it is valuable for advancing our knowledge of cellular functions and can benefit life science research, clinical diagnostics, and environmental monitoring. Incorporating imaging capabilities into flow cytometry compromises the assay throughput, primarily due to the limitations on speed and sensitivity in the camera technologies. To overcome this speed or throughput challenge facing imaging flow cytometry while preserving the image quality, asymmetric-detection time-stretch optical microscopy (ATOM) has been demonstrated to enable high-contrast, single-cell imaging with sub-cellular resolution, at an imaging throughput as high as 100,000 cells/s. Based on the imaging concept of conventional time-stretch imaging, which relies on all-optical image encoding and retrieval through the use of ultrafast broadband laser pulses, ATOM further advances imaging performance by enhancing the image contrast of unlabeled/unstained cells. This is achieved by accessing the phase-gradient information of the cells, which is spectrally encoded into single-shot broadband pulses. Hence, ATOM is particularly advantageous in high-throughput measurements of single-cell morphology and texture - information indicative of cell types, states, and even functions. Ultimately, this could become a powerful imaging flow cytometry platform for the biophysical phenotyping of cells, complementing the current state-of-the-art biochemical-marker-based cellular assay. This work describes a protocol to establish the key modules of an ATOM system (from optical frontend to data processing and visualization backend), as well as the workflow of imaging flow cytometry based on ATOM, using human cells and micro-algae as the examples.

Main Building (4800) at Dryden FRC

NASA Image and Video Library

1991-09-05

The X-1E research aircraft provides a striking view at the entrance of NASA's Dryden Flight Research Center, Edwards, California. The X-1E, one of the three original X-1 aircraft modified with a raised cockpit canopy and an ejection seat, was flown at the facility between 1953 and 1958 to investigate speeds at twice that of sound, and also to evaluate a thin wing designed for high-speed flight. The Dryden complex was originally established in 1946 as a small high-speed flight station to support the X-1 program. The X-1 was the first aircraft to fly at supersonic speeds. The main administrative building is to the rear of the X-1E and is the center of a research installation that has grown to more than 450 government employees and nearly 400 civilian contractors. Located on the northwest "shore" of Rogers Dry Lake, the Dryden Center was built around the original administrative-hangar building constructed in 1954 at a cost of $3.8 million. Since then many additional support and operational facilities have been built including a number of unique test facilities such as the Thermalstructures Research Facility, Flow Visualization Facility, and the newest addition, the Integrated Test Facility.

An experimental study of combustion: The turbulent structure of a reacting shear layer formed at a rearward-facing step. Ph.D. Thesis. Final Report

NASA Technical Reports Server (NTRS)

Pitz, R. W.

1981-01-01

A premixed propane-air flame is stabilized in a turbulent free shear layer formed at a rearward-facing step. The mean and rms averages of the turbulent velocity flow field were determined by LDV for both reacting and non-reacting flows. The reaching flow was visualized by high speed schlieren photography. Large scale structures dominate the reacting shear layer. The growth of the large scale structures is tied to the propagation of the flame. The linear growth rate of the reacting shear layer defined by the mean velocity profiles is unchanged by combustion but the virtual origin is shifted downstream. The reacting shear layer based on the mean velocity profiles is shifted toward the recirculation zone and the reattachments lengths are shortened by 30%.

Remote visual analysis of large turbulence databases at multiple scales

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pulido, Jesus; Livescu, Daniel; Kanov, Kalin

The remote analysis and visualization of raw large turbulence datasets is challenging. Current accurate direct numerical simulations (DNS) of turbulent flows generate datasets with billions of points per time-step and several thousand time-steps per simulation. Until recently, the analysis and visualization of such datasets was restricted to scientists with access to large supercomputers. The public Johns Hopkins Turbulence database simplifies access to multi-terabyte turbulence datasets and facilitates the computation of statistics and extraction of features through the use of commodity hardware. In this paper, we present a framework designed around wavelet-based compression for high-speed visualization of large datasets and methodsmore » supporting multi-resolution analysis of turbulence. By integrating common technologies, this framework enables remote access to tools available on supercomputers and over 230 terabytes of DNS data over the Web. Finally, the database toolset is expanded by providing access to exploratory data analysis tools, such as wavelet decomposition capabilities and coherent feature extraction.« less

Remote visual analysis of large turbulence databases at multiple scales

DOE PAGES

Pulido, Jesus; Livescu, Daniel; Kanov, Kalin; ...

2018-06-15

The remote analysis and visualization of raw large turbulence datasets is challenging. Current accurate direct numerical simulations (DNS) of turbulent flows generate datasets with billions of points per time-step and several thousand time-steps per simulation. Until recently, the analysis and visualization of such datasets was restricted to scientists with access to large supercomputers. The public Johns Hopkins Turbulence database simplifies access to multi-terabyte turbulence datasets and facilitates the computation of statistics and extraction of features through the use of commodity hardware. In this paper, we present a framework designed around wavelet-based compression for high-speed visualization of large datasets and methodsmore » supporting multi-resolution analysis of turbulence. By integrating common technologies, this framework enables remote access to tools available on supercomputers and over 230 terabytes of DNS data over the Web. Finally, the database toolset is expanded by providing access to exploratory data analysis tools, such as wavelet decomposition capabilities and coherent feature extraction.« less

Multi-Scale Visualization Analysis of Bus Flow Average Travel Speed in Qingdao

NASA Astrophysics Data System (ADS)

Yong, HAN; Man, GAO; Xiao-Lei, ZHANG; Jie, LI; Ge, CHEN

2016-11-01

Public transportation is a kind of complex spatiotemporal behaviour. The traffic congestion and environmental pollution caused by the increase in private cars is becoming more and more serious in our city. Spatiotemporal data visualization is an effective tool for studying traffic, transforming non-visual data into recognizable images, which can reveal where/when congestion is formed, developed and disappeared in space and time simultaneously. This paper develops a multi-scale visualization of average travel speed derived from floating bus data, to enable congestion on urban bus networks to be shown and analyzed. The techniques of R language, Echarts, WebGL are used to draw statistical pictures and 3D wall map, which show the congestion in Qingdao from the view of space and time. The results are as follows:(1) There is a more severely delay in Shibei and Shinan areas than Licun and Laoshan areas; (2) The high congestion usually occurs on Hong Kong Middle Road, Shandong Road, Nanjing Road, Liaoyang West Road and Taiping Road;(3) There is a similar law from Monday to Sunday that the congestion is severer in the morning and evening rush hours than other hours; (4) On Monday morning the severity of congestion is higher than on Friday morning, and on Friday evening the severity is higher than on Monday evening. The research results will help to improve the public transportation of Qingdao.

High-speed cell recognition algorithm for ultrafast flow cytometer imaging system.

PubMed

Zhao, Wanyue; Wang, Chao; Chen, Hongwei; Chen, Minghua; Yang, Sigang

2018-04-01

An optical time-stretch flow imaging system enables high-throughput examination of cells/particles with unprecedented high speed and resolution. A significant amount of raw image data is produced. A high-speed cell recognition algorithm is, therefore, highly demanded to analyze large amounts of data efficiently. A high-speed cell recognition algorithm consisting of two-stage cascaded detection and Gaussian mixture model (GMM) classification is proposed. The first stage of detection extracts cell regions. The second stage integrates distance transform and the watershed algorithm to separate clustered cells. Finally, the cells detected are classified by GMM. We compared the performance of our algorithm with support vector machine. Results show that our algorithm increases the running speed by over 150% without sacrificing the recognition accuracy. This algorithm provides a promising solution for high-throughput and automated cell imaging and classification in the ultrafast flow cytometer imaging platform. (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE).

High-speed cell recognition algorithm for ultrafast flow cytometer imaging system

NASA Astrophysics Data System (ADS)

Zhao, Wanyue; Wang, Chao; Chen, Hongwei; Chen, Minghua; Yang, Sigang

2018-04-01

An optical time-stretch flow imaging system enables high-throughput examination of cells/particles with unprecedented high speed and resolution. A significant amount of raw image data is produced. A high-speed cell recognition algorithm is, therefore, highly demanded to analyze large amounts of data efficiently. A high-speed cell recognition algorithm consisting of two-stage cascaded detection and Gaussian mixture model (GMM) classification is proposed. The first stage of detection extracts cell regions. The second stage integrates distance transform and the watershed algorithm to separate clustered cells. Finally, the cells detected are classified by GMM. We compared the performance of our algorithm with support vector machine. Results show that our algorithm increases the running speed by over 150% without sacrificing the recognition accuracy. This algorithm provides a promising solution for high-throughput and automated cell imaging and classification in the ultrafast flow cytometer imaging platform.

A two-angle far-field microscope imaging technique for spray flows

NASA Astrophysics Data System (ADS)

Kourmatzis, Agisilaos; Pham, Phuong X.; Masri, Assaad R.

2017-03-01

Backlight imaging is frequently used for the visualization of multiphase flows, where with appropriate microscope lenses, quantitative information on the spray structure can be attained. However, a key issue resides in the nature of the measurement which relies on a single viewing angle, hence preventing imaging of all liquid structures and features, such as those located behind other fragments. This paper presents results from an extensive experimental study aimed as a step forward towards resolving this problem by using a pair of high speed cameras oriented at 90 degrees to each other, and synchronized to two high-speed diode lasers. Both cameras are used with long distance microscope lenses. The images are processed as pairs allowing for identification and classification of the same liquid structure from two perspectives at high temporal (5 kHz) and spatial resolution (∼3 μm). Using a controlled mono-disperse spray, simultaneous, time-resolved visualization of the same spherical object being focused on one plane while de-focused on the other plane 90 degrees to the first has allowed for a quantification of shot-to-shot defocused size measurement error. An extensive error analysis is performed for spheroidal structures imaged from two angles and the dual angle technique is extended to measure the volume of non-spherical fragments for the first time, by ‘discretising’ a fragment into a number of constituent ellipses. Error analysis is performed based on measuring the known volumes of solid arbitrary shapes, and volume estimates were found to be within  ∼11% of the real volume for representative ‘ligament-like’ shapes. The contribution concludes by applying the ellipsoidal method to a real spray consisting of multiple non-spherical fragments. This extended approach clearly demonstrates potential to yield novel volume weighted quantities of non-spherical objects in turbulent multiphase flow applications.

Plasma measurement by optical visualization and triple probe method under high-speed impact

NASA Astrophysics Data System (ADS)

Sakai, T.; Umeda, K.; Kinoshita, S.; Watanabe, K.

2017-02-01

High-speed impact on spacecraft by space debris poses a threat. When a high-speed projectile collides with target, it is conceivable that the heat created by impact causes severe damage at impact point. Investigation of the temperature is necessary for elucidation of high-speed impact phenomena. However, it is very difficult to measure the temperature with standard methods for two main reasons. One reason is that a thermometer placed on the target is instantaneously destroyed upon impact. The other reason is that there is not enough time resolution to measure the transient temperature changes. In this study, the measurement of plasma induced by high-speed impact was investigated to estimate temperature changes near the impact point. High-speed impact experiments were performed with a vertical gas gun. The projectile speed was approximately 700 m/s, and the target material was A5052. The experimental data to calculate the plasma parameters of electron temperature and electron density were measured by triple probe method. In addition, the diffusion behavior of plasma was observed by optical visualization technique using high-speed camera. The frame rate and the exposure time were 260 kfps and 1.0 μs, respectively. These images are considered to be one proof to show the validity of plasma measurement. The experimental results showed that plasma signals were detected for around 70 μs, and the rising phase of the wave form was in good agreement with timing of optical visualization image when the plasma arrived at the tip of triple probe.

The role of vision in odor-plume tracking by walking and flying insects.

PubMed

Willis, Mark A; Avondet, Jennifer L; Zheng, Elizabeth

2011-12-15

The walking paths of male cockroaches, Periplaneta americana, tracking point-source plumes of female pheromone often appear similar in structure to those observed from flying male moths. Flying moths use visual-flow-field feedback of their movements to control steering and speed over the ground and to detect the wind speed and direction while tracking plumes of odors. Walking insects are also known to use flow field cues to steer their trajectories. Can the upwind steering we observe in plume-tracking walking male cockroaches be explained by visual-flow-field feedback, as in flying moths? To answer this question, we experimentally occluded the compound eyes and ocelli of virgin P. americana males, separately and in combination, and challenged them with different wind and odor environments in our laboratory wind tunnel. They were observed responding to: (1) still air and no odor, (2) wind and no odor, (3) a wind-borne point-source pheromone plume and (4) a wide pheromone plume in wind. If walking cockroaches require visual cues to control their steering with respect to their environment, we would expect their tracks to be less directed and more variable if they cannot see. Instead, we found few statistically significant differences among behaviors exhibited by intact control cockroaches or those with their eyes occluded, under any of our environmental conditions. Working towards our goal of a comprehensive understanding of chemo-orientation in insects, we then challenged flying and walking male moths to track pheromone plumes with and without visual feedback. Neither walking nor flying moths performed as well as walking cockroaches when there was no visual information available.

The role of vision in odor-plume tracking by walking and flying insects

PubMed Central

Willis, Mark A.; Avondet, Jennifer L.; Zheng, Elizabeth

2011-01-01

SUMMARY The walking paths of male cockroaches, Periplaneta americana, tracking point-source plumes of female pheromone often appear similar in structure to those observed from flying male moths. Flying moths use visual-flow-field feedback of their movements to control steering and speed over the ground and to detect the wind speed and direction while tracking plumes of odors. Walking insects are also known to use flow field cues to steer their trajectories. Can the upwind steering we observe in plume-tracking walking male cockroaches be explained by visual-flow-field feedback, as in flying moths? To answer this question, we experimentally occluded the compound eyes and ocelli of virgin P. americana males, separately and in combination, and challenged them with different wind and odor environments in our laboratory wind tunnel. They were observed responding to: (1) still air and no odor, (2) wind and no odor, (3) a wind-borne point-source pheromone plume and (4) a wide pheromone plume in wind. If walking cockroaches require visual cues to control their steering with respect to their environment, we would expect their tracks to be less directed and more variable if they cannot see. Instead, we found few statistically significant differences among behaviors exhibited by intact control cockroaches or those with their eyes occluded, under any of our environmental conditions. Working towards our goal of a comprehensive understanding of chemo-orientation in insects, we then challenged flying and walking male moths to track pheromone plumes with and without visual feedback. Neither walking nor flying moths performed as well as walking cockroaches when there was no visual information available. PMID:22116754

Annular flow in rod-bundle: Effect of spacer on disturbance waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pham, Son H.; Kunugi, Tomoaki

2016-08-01

A high-speed camera technique is used to study the effect of spacers on the disturbance waves present in annular two-phase flow within a rod-bundle geometry. Images obtained using a backlight configuration to visualize the spacer-wave interactions at the micro-scale resolution (in time and space) are discussed. This paper also presents additional images obtained using a reflected light configuration which provides new observations of the disturbance waves. These images show the separation effect caused by the spacer on the liquid film in which the size of generated liquid droplets can be controlled by the gas superficial velocity. Furthermore, the data confirmmore » that the spacer breaks the circumferential coherent structures of the waves.« less

Tip Vortex Cavitation

NASA Astrophysics Data System (ADS)

Maines, Brant H.; Arndt, Roger E. A.

2000-11-01

Cavitation in vortical flows is a problem of practical importance, that is relatively unexplored. Vortical structures of importance range from the eddies occurring randomly in space and time in turbulent flows to the developed vortices that occur at the tips of lifting surfaces and at the hubs of propellers and hydraulic turbines. A variety of secondary flow phenomena such as the horse shoe vortices that form around bridge piers, chute blocks and struts, and the secondary vortices found in the clearance passages of turbomachinery are also important cavitation sites. Tip vortex cavitation can be viewed as a canonical problem that captures many of the essential physics associated with vortex cavitation in general. This paper describes the inception process and focuses on the high levels of tension that can be sustained in the flow, which appears to scale with the blade loading. High speed video visualization indicates that the details of how free stream nuclei are ingested plays a major role in the nucleation and inception process. A new photographic technique was used to obtain high quality images of the bubble growth process at framing rates as high as 40,000 fps. Sponsored by the Office of Naval Research

Interfacial instability of wormlike micellar solutions sheared in a Taylor-Couette cell

NASA Astrophysics Data System (ADS)

Mohammadigoushki, Hadi; Muller, Susan J.

2014-11-01

We report experiments on wormlike micellar solutions sheared in a custom-made Taylor-Couette (TC) cell. The computer controlled TC cell allows us to rotate both cylinders independently. Wormlike micellar solutions containing water, CTAB, and NaNo3 with different compositions are highly elastic and exhibit shear banding. We visualized the flow field in the θ-z as well as r-z planes, using multiple cameras. When subject to low shear rates, the flow is stable and azimuthal, but becomes unstable above a certain threshold shear rate. This shear rate coincides with the onset of shear banding. Visualizing the θ-z plane shows that this instability is characterized by stationary bands equally spaced in the z direction. Increasing the shear rate results to larger wave lengths. Above a critical shear rate, experiments reveal a chaotic behavior reminiscent of elastic turbulence. We also studied the effect of ramp speed on the onset of instability and report an acceleration below which the critical Weissenberg number for onset of instability is unaffected. Moreover, visualizations in the r-z direction reveals that the interface between the two bands undulates with shear bands evolving towards the outer cylinder regardless of which cylinder is rotating.

Visualization of Flowfield Modification by RCS Jets on a Capsule Entry Vehicle

NASA Technical Reports Server (NTRS)

Danehy, P. M.; Inman, J. A.; Alderfer, D. W.; Buck, G. M.; Schwartz, R.

2008-01-01

Nitric oxide planar laser-induced fluorescence (NO PLIF) has been used to visualize the flow on the aft-body of an entry capsule having an activated RCS jet in NASA Langley Research Center's 31-Inch Mach 10 wind tunnel facility. A capsule shape representative of the Apollo command module was tested. These tests were performed to demonstrate the ability of the PLIF method to visualize RCS jet flow while providing some preliminary input to NASA's Orion Vehicle design team. Two different RCS nozzle designs - conical and contoured - were tested. The conical and contoured nozzles had area ratios of 13.4 and 22.5 respectively. The conical nozzle had a half-angle of 10 . Low- and high-Reynolds number cases were investigated by changing the tunnel stagnation pressure from 350 psi to 1300 psi, resulting in freestream Reynolds numbers of 0.56 and 1.8 million per foot respectively. For both of these cases, three different jet plenum pressures were tested (nominally 56, 250 and 500 psi). A single angle-of-attack was investigated (24 degrees). NO PLIF uses an ultraviolet laser sheet to interrogate a slice in the flow containing seeded NO; this UV light excites fluorescence from the NO molecules which is detected by a high-speed digital camera. The system has spatial resolution of about 200 microns (2 pixel blurring) and has flow-stopping time resolution (approximately 1 microsecond). NO was seeded into the flow two different ways. First, the RCS jet fluid was seeded with approximately 1-5% NO, with the balance N2. This allowed observation of the shape, structure and trajectory of the RCS jets. Visualizations of both laminar and turbulent flow jet features were obtained. Visualizations were obtained with the tunnel operating at Mach 10 and also with the test section held at a constant pressure similar to the aftbody static pressure (0.04 psi) obtained during tunnel runs. These two conditions are called "tunnel on" and "tunnel off" respectively. Second, the forebody flow was seeded with a very low flowrate (<100 standard cubic centimeters per minute) of pure NO. This trace gas was entrained into and allowed visualization of the shear layer forming between the expansion fan on the shoulder of the model and the recirculating separated flow in the wake of the model. This shear layer was observed to be laminar in the absence of the RCS jet operation and turbulent above a certain RCS jet flowrate. Furthermore, the operation of the RCS jet is seen to push the shear layer out away from the model, with a higher jet pressures resulting in larger deflections. Figures show some data from this test, partially processed. In the final paper, these images will be processed and rendered on a three dimensional visualization of the test hardware for clearer visualization and interpretation of the flowfields.

Effect of mass and charge transport speed and direction in porous anodes on microbial electrolysis cell performance.

PubMed

Sleutels, Tom H J A; Hamelers, Hubertus V M; Buisman, Cees J N

2011-01-01

The use of porous electrodes like graphite felt as anode material has the potential of achieving high volumetric current densities. High volumetric current densities, however, may also lead to mass transport limitations within these porous materials. Therefore, in this study we investigated the mass and charge transport limitations by increasing the speed of the forced flow and changing the flow direction through the porous anode. Increase of the flow speed led to a decrease in current density when the flow was directed towards the membrane caused by an increase in anode resistance. Current density increased at higher flow speed when the flow was directed away from the membrane. This was caused by a decrease in transport resistance of ions through the membrane which increased the buffering effect of the system. Furthermore, the increase in flow speed led to an increase of the coulombic efficiency by 306%. Copyright © 2010 Elsevier Ltd. All rights reserved.

Two-Dimensional Bifurcated Inlet Variable Cowl Lip Test Completed in 10- by 10-Foot Supersonic Wind Tunnel

NASA Technical Reports Server (NTRS)

Hoffman, T. R.

2000-01-01

Researchers at the NASA Glenn Research Center at Lewis Field successfully tested a variable cowl lip inlet at simulated takeoff conditions in Glenn s 10- by 10-Foot Supersonic Wind Tunnel (10x10 SWT) as part of the High-Speed Research Program. The test was a follow-on to the Two-Dimensional Bifurcated (2DB) Inlet/Engine test. At the takeoff condition for a High-Speed Civil Transport aircraft, the inlet must provide adequate airflow to the engine with an acceptable distortion level and high-pressure recovery. The test was conducted to study the effectiveness of installing two rotating lips on the 2DB Inlet cowls to increase mass flow rate and eliminate or reduce boundary layer flow separation near the lips. Hardware was mounted vertically in the test section so that it extended through the tunnel ceiling and that the 2DB Inlet was exposed to the atmosphere above the test section. The tunnel was configured in the aerodynamic mode, and exhausters were used to pump down the tunnel to vacuum levels and to provide a maximum flow rate of approximately 58 lb/sec. The test determined the (1) maximum flow in the 2DB Inlet for each variable cowl lip, (2) distortion level and pressure recovery for each lip configuration, (3) boundary layer conditions near variable lips inside the 2DB Inlet, (4) effects of a wing structure adjacent to the 2DB Inlet, and (5) effects of different 2DB Inlet exit configurations. It also employed flow visualization to generate enough qualitative data on variable lips to optimize the variable lip concept. This test was a collaborative effort between the Boeing Company and Glenn. Extensive inhouse support at Glenn contributed significantly to the progress and accomplishment of this test.

An apparatus for generation and quantitative measurement of homogeneous isotropic turbulence in He ii

NASA Astrophysics Data System (ADS)

Mastracci, Brian; Guo, Wei

2018-01-01

The superfluid phase of helium-4, known as He ii, exhibits extremely small kinematic viscosity and may be a useful tool for economically producing and studying high Reynolds number turbulent flow. Such applications are not currently possible because a comprehensive understanding of the complex two-fluid behavior of He ii is lacking. This situation could be remedied by a systematic investigation of simple, well controlled turbulence that can be directly compared with theoretical models. To this end, we have developed a new apparatus that combines flow visualization with second sound attenuation to study turbulence in the wake of a mesh grid towed through a He ii filled channel. One of three mesh grids (mesh number M = 3, 3.75, or 5 mm) can be pulled at speeds between 0.1 and 60 cm/s through a cast acrylic flow channel which has a 16 mm × 16 mm cross section and measures 330 mm long. The motion of solidified deuterium tracer particles, with diameter of the order 1 μm, in the resulting flow is captured by a high speed camera, and a particle tracking velocimetry algorithm resolves the Lagrangian particle trajectories through the turbulent flow field. A pair of oscillating superleak second sound transducers installed in the channel allows complementary measurement of vortex line density in the superfluid throughout the turbulent decay process. Success in early experiments demonstrates the effectiveness of both probes, and preliminary analysis of the data shows that both measurements strongly correlate with each other. Further investigations will provide comprehensive information that can be used to address open questions about turbulence in He ii and move toward the application of this fluid to high Reynolds number fluid research.

Method for transition prediction in high-speed boundary layers, phase 2

NASA Astrophysics Data System (ADS)

Herbert, T.; Stuckert, G. K.; Lin, N.

1993-09-01

The parabolized stability equations (PSE) are a new and more reliable approach to analyzing the stability of streamwise varying flows such as boundary layers. This approach has been previously validated for idealized incompressible flows. Here, the PSE are formulated for highly compressible flows in general curvilinear coordinates to permit the analysis of high-speed boundary-layer flows over fairly general bodies. Vigorous numerical studies are carried out to study convergence and accuracy of the linear-stability code LSH and the linear/nonlinear PSE code PSH. Physical interfaces are set up to analyze the M = 8 boundary layer over a blunt cone calculated by using a thin-layer Navier Stokes (TNLS) code and the flow over a sharp cone at angle of attack calculated using the AFWAL parabolized Navier-Stokes (PNS) code. While stability and transition studies at high speeds are far from routine, the method developed here is the best tool available to research the physical processes in high-speed boundary layers.

Use of schlieren methods to study gas flow in laser technology

NASA Astrophysics Data System (ADS)

Mrňa, Libor; Pavelka, Jan; Horník, Petr; Hrabovský, Jozef

2016-11-01

Laser technologies such as welding and cutting rely on process gases. We suggest to use schlieren imaging to visualize the gas flow during these processes. During the process of laser welding, the shielding gas flows to the welded area to prevent oxidation of the weld pool by surrounding air. The gas also interacts with hot plasma spurting from the key hole induced by the laser beam incident on the molten material. This interaction is quite complicated because hot plasma mixes with the cold shielding gas while the system is moving along the weld. Three shielding gases were used in the presented experiment: Ar, He and N2. Differences in dynamics of the flow are clearly visible on schlieren images. Moreover, high speed recording reveals a structure consisting of hot gas bubbles. We were also able to determine the velocity of the bubbles from the recording. During laser cutting, the process gas flows coaxially with the laser beam from the nozzle to remove the molten material out of the kerf. The gas flow is critical for the quality of the resulting edge of the cut. Schlieren method was used to study gas flow under the nozzle and then under the material being cut. This actually creates another slot nozzle. Due to the very low speed of flow below the material the schleiren method is already at the limit of its sensitivity. Therefore, it is necessary to apply a differential technique to increase the contrast. Distinctive widening of the flow shaped by the kerf was observed.

The effect of the chopper on granules from wet high-shear granulation using a PMA-1 granulator.

PubMed

Briens, Lauren; Logan, Ryan

2011-12-01

Chopper presence and then chopper speed was varied during wet high shear granulation of a placebo formulation using a PMA-1 granulator while also varying the impeller speed. The granules were extensively analyzed for differences due to the chopper. The effect of the chopper on the granules varied with impeller speed from no effect at a low impeller speed of 300 rpm to flow interruptions at an impeller speed of 700 rpm to minimal impact at very high impeller speeds as caking at the bowl perimeter obscured the effect of the chopper on the flow pattern. Differences in the granule flowability were minimal. However, it was concluded that the largest fraction of optimal granules would be obtained at an impeller speed of 700 rpm with the chopper at 1,000 rpm allowing balances between flow establishment, segregation, and centrifugal forces.

Fluid mechanics and heat transfer spirally fluted tubing

NASA Astrophysics Data System (ADS)

Yampolsky, J. S.; Libby, P. A.; Launder, B. E.; Larue, J. C.

1984-12-01

The objective of this program is to develop an understanding of the fluid mechanics and heat transfer mechanisms that result in the demonstrated performance of the spiral fluted tubing under development at GA Technologies Inc. Particularly emphasized are the processes that result in the augmentation of the heat transfer coefficient without an increase in friction coefficient in the single-phase flow. Quantitative delineation of these processes would allow for their application to the optimal solution of heat transfer problems in general was well as to tubular heat exchanges using spiral fluted tubes. The experimental phase of the program consisted of the following: (1) Flow visualization studies using high-speed photography of dye injected into water flowing in a cast acrylic spiral fluted tube. (2) Time-resolved axial velocity measurements as a function of radius at the exit plane of a spiral fluted tube with water flowing through the tube. (3) Simultaneous time-resolved measurements of the axial and radial velocity components and temperature with heated air flowing through the tube cooled by a water jacket.

Two-phase flow research using the DC-9/KC-135 apparatus

NASA Technical Reports Server (NTRS)

McQuillen, John B.; Neumann, Eric S.; Shoemaker, J. Michael

1996-01-01

Low-gravity gas-liquid flow research can be conducted aboard the NASA Lewis Research Center DC-9 or the Johnson Space Center KC-135. Air and water solutions serve as the test liquids in cylindrical test sections with constant or variable inner diameters of approximately 2.54 cm and lengths of up to 3.0 m. Superficial velocities range from 0.1 to 1.1 m/sec for liquids and from 0.1 to 25 m/sec for air. Flow rate, differential pressure, void fraction, film thickness, wall shear stress, and acceleration data are measured and recorded at data rates of up to 1000 Hz throughout the 20-sec duration of the experiment. Flow is visualized with a high-speed video system. In addition, the apparatus has a heat-transfer capability whereby sensible heat is transferred between the test-section wall and a subcooled liquid phase so that the heat-transfer characteristics of gas-liquid two-phase flows can be determined.

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

Characterization of the Boundary Layer on Full-Scale Bluefin Tuna

NASA Astrophysics Data System (ADS)

Amaral, Brian; Cipolla, Kimberly; Henoch, Charles

2014-11-01

The physics that enable tuna to cross large expanses of ocean while feeding and avoiding predators is not presently understood, and could involve complex control of turbulent boundary layer transition and drag reduction. Typical swimming speeds of Bluefin tuna are 1-2 m/s, but can be higher during strong accelerations. The goal of this work is to experimentally determine the approximate lateral location at which transition to turbulence occurs on the tuna for various speeds. The question is whether laminar flow or an advanced propulsion mechanism (or both) allows them to swim at high speeds. Uncertainties include the surface roughness of the skin, local favorable and adverse pressure gradients, and discontinuities such as the open mouth or juncture at the fins. Historically, much of the fluid mechanics work in the area of fish locomotion has focused on vortex shedding issues rather than the boundary layer. Here, the focus is obtaining information on the boundary layer characteristics of a rigid tuna model. A full scale model of a Pacific Bluefin tuna was fabricated using a mold made from an actual deceased tuna, preserving the surface features and details of the appendages. The model was instrumented with 32 wall pressure sensors and experiments performed in a tow tank. Results from flow visualization, drag and wall pressure measurements over a range of speeds and varying angles of attack will be presented.

Metal flow and temperature in direct extrusion of large-size aluminum billets

NASA Astrophysics Data System (ADS)

Valberg, Henry; Costa, André L. M.

2018-05-01

FEM-analysis is used to study thermo-mechanical conditions in aluminum rod extrusion for billets with large size corresponding to that used in industrial production. In the analysis, focus is on how the metal flow and the temperature conditions in the extrusion material is affected by the extrusion velocity in terms of the ram speed used in the extrusion process. In the study, metal flow is characterized by the deformations in extrusion subjected to a perfect grid pattern, consisting of orthogonal crossing lines, added into the longitudinal mid-plane of the initial billet. The analysis shows that metal flow in extrusion conducted at a low ram speed of 1 mms-1, is predicted significantly different from that at a high speed of 5 mms-1, or above. As regards the thermal conditions in the extrusion material, they are also predicted significantly different, at the low and the high ram speed level. A likely explanation why metal flow is different at low and high ram speeds may be that flow is altered because of the concurrent change in the temperature field within the billet.

High-tip-speed, low-loading transonic fan stage. Part 3: Final report

NASA Technical Reports Server (NTRS)

Ware, T. C.; Kobayashi, R. J.; Jackson, R. J.

1974-01-01

Tests were conducted on a high-tip-speed, low-loading transonic fan stage to determine the performance and inlet flow distortion tolerance of the design. The fan was designed for high efficiency at a moderate pressure ratio by designing the hub section to operate at minimum loss when the tip operates with an oblique shock. The design objective was an efficiency of 86 percent at a pressure ratio of 1.5, a specific flow (flow per unit annulus area) of 42 lb/sec-sq. ft (205.1 kgm/sec-m sq), and a tip speed of 1600 ft/sec (488.6 m/sec). During testing, a peak efficiency of 84 percent was achieved at design speed and design specific flow. At the design speed and pressure ratio, the flow was 4 percent greater than design, efficiency was 81 percent, and a stall margin of 24 percent was obtained. The stall line was improved with hub radial distortion but was reduced when the stage was tested with tip radial and circumferential flow distortions. Blade-to-blade values of static pressures were measured over the rotor blade tips.

Blood flow speed of the gastric conduit assessed by indocyanine green fluorescence

PubMed Central

Koyanagi, Kazuo; Ozawa, Soji; Oguma, Junya; Kazuno, Akihito; Yamazaki, Yasushi; Ninomiya, Yamato; Ochiai, Hiroki; Tachimori, Yuji

2016-01-01

Abstract Anastomotic leakage is considered as an independent risk factor for postoperative mortality after esophagectomy, and an insufficient blood flow in the reconstructed conduit may be a risk factor of anastomotic leakage. We investigated the clinical significance of blood flow visualization by indocyanine green (ICG) fluorescence in the gastric conduit as a means of predicting the leakage of esophagogastric anastomosis after esophagectomy. Forty patients who underwent an esophagectomy with gastric conduit reconstruction were prospectively investigated. ICG fluorescence imaging of the gastric conduit was detected by a near-infrared camera system during esophagectomy and correlated with clinical parameters or surgical outcomes. In 25 patients, the flow speed of ICG fluorescence in the gastric conduit wall was simultaneous with that of the greater curvature vessels (simultaneous group), whereas in 15 patients this was slower than that of the greater curvature vessels (delayed group). The reduced speed of ICG fluorescence stream in the gastric conduit wall was associated with intraoperative blood loss (P = 0.008). Although anastomotic leakage was not found in the simultaneous group, it occurred in 7 patients of the delayed group (P < 0.001). A flow speed of ICG fluorescence in the gastric conduit wall of 1.76 cm/s or less was determined by a receiver operating characteristic (ROC) curve, identified as a significant independent predictor of anastomotic leakage after esophagectomy (P = 0.004). This preliminary study demonstrates that intraoperative evaluation of blood flow speed by ICG fluorescence in the gastric conduit wall is a useful means to predict the risk of anastomotic leakage after esophagectomy. PMID:27472732

Global Visualization in Water using AnodizedAluminum PressureSensitive Paint and Dissolved Oxygen as Tracer

NASA Astrophysics Data System (ADS)

Ozaki, Tatsuya; Ishikawa, Hitoshi; Sakaue, Hirotaka

2009-11-01

We have developed anodized-aluminum pressuresensitive paint (AA-PSP) for flow visualization in water using dissolved oxygen as a tracer. Developed AA-PSP is characterized using water calibration setup by controlling a dissolved oxygen concentration. It is shown that the developed AA-PSP gives 4.0 percent change in luminescence per 1 mg/l of oxygen concentration. This AA-PSP is applied to visualize flows in a water tunnel. Oxygen concentrations of the water tunnel and the dissolved oxygen are 9.5 mg/l and 20 mg/l, respectively. We can capture horseshoe vortices over the base of 10 mm cylinder by using this technique at Reynolds number of 1000 and a water speed of 100 mm/s, respectively. Unlike conventional tracers such as ink, milk, and fluorescent dyes, this visualization technique gives flow information on the AA-PSP coated surface without integrating flows between the AA-PSP and an optical detector. Because of using dissolved oxygen as a tracer, it holds the material properties of testing water except for the amount of oxygen. The tracer does not interfere with optical measurements and it does not contaminate the testing water. A conventional visualization technique using milk as a tracer is also employed for comparison.

Interaction of gusts with forest edges

NASA Astrophysics Data System (ADS)

Ruck, Bodo; Tischmacher, Michael

2012-05-01

Experimental investigations in an atmospheric boundary layer wind tunnel were carried out in order to study the interaction of gusts with forest edges. Summarizing the state of knowledge in the field of forest damages generated by extreme storms, there is a strong indication that in many cases, windthrow of trees starts near the forest edge from where it spreads into the stand. The high-transient interaction between gusts and (porous) forest edges produce unsteady flow phenomena not known so far. From a fluid mechanical point of view, the flow type resembles a forward-facing porous step flow, which is significantly influenced by the characteristics of the oncoming atmospheric boundary layer flow and the shape and `porous properties' of the forest edge. The paper reports systematic investigations on the interaction of artificially generated gusts and forest edge models in an atmospheric boundary layer wind tunnel. The experimental investigations were carried out with a laser-based time-resolved PIV-system and high speed photography. Different flow phenomena like gust streching, vortex formation, Kelvin-Helmholtz instabilities or wake production of turbulence could be measured or visualized contributing to the understanding of the complex flow perfomance over the forest edge.

Qualitative Flow Visualization of a 110-N Hydrogen/Oxygen Laboratory Model Thruster

NASA Technical Reports Server (NTRS)

deGroot, Wim A.; McGuire, Thomas J.; Schneider, Steven J.

1997-01-01

The flow field inside a 110 N gaseous hydrogen/oxygen thruster was investigated using an optically accessible, two-dimensional laboratory test model installed in a high altitude chamber. The injector for this study produced an oxidizer-rich core flow, which was designed to fully mix and react inside a fuel-film sleeve insert before emerging into the main chamber section, where a substantial fuel film cooling layer was added to protect the chamber wall. Techniques used to investigate the flow consisted of spontaneous Raman spectra measurements, visible emission imaging, ultraviolet hydroxyl spectroscopy, and high speed schlieren imaging. Experimental results indicate that the oxygen rich core flow continued to react while emerging from the fuel-film sleeve, suggesting incomplete mixing of the hydrogen in the oxygen rich core flow. Experiments also showed that the fuel film cooling protective layer retained its integrity throughout the straight section of the combustion chamber. In the converging portion of the chamber, however, a turbulent reaction zone near the wall destroyed the integrity of the film layer, a result which implies that a lower contraction angle may improve the fuel film cooling in the converging section and extend the hardware lifetime.

Conveying Looming with a Localized Tactile Cue

DTIC Science & Technology

2015-04-01

leaning and reflexive head righting required at different speeds of linear or angular motion, the angle of contact of the foot to the substrate (e.g...approach information (e.g., relative distance updates) prior to actual contact , as has been reported for visual and auditory displays. A few studies have...Jacobs, 2013). Cancar et al. asked 12 subjects to estimate time-to- contact of a radially-expanding tactile or visual flow field representing a

High-Speed Lateral Flow Strategy for a Fast Biosensing with an Improved Selectivity and Binding Affinity.

PubMed

Cho, Dong Guk; Yoo, Haneul; Lee, Haein; Choi, Yeol Kyo; Lee, Minju; Ahn, Dong June; Hong, Seunghun

2018-05-10

We report a high-speed lateral flow strategy for a fast biosensing with an improved selectivity and binding affinity even under harsh conditions. In this strategy, biosensors were fixed at a location away from the center of a round shape disk, and the disk was rotated to create the lateral flow of a target solution on the biosensors during the sensing measurements. Experimental results using the strategy showed high reaction speeds, high binding affinity, and low nonspecific adsorptions of target molecules to biosensors. Furthermore, binding affinity between target molecules and sensing molecules was enhanced even in harsh conditions such as low pH and low ionic strength conditions. These results show that the strategy can improve the performance of conventional biosensors by generating high-speed lateral flows on a biosensor surface. Therefore, our strategy can be utilized as a simple but powerful tool for versatile bio and medical applications.

A Full Body Steerable Wind Display for a Locomotion Interface.

PubMed

Kulkarni, Sandip D; Fisher, Charles J; Lefler, Price; Desai, Aditya; Chakravarthy, Shanthanu; Pardyjak, Eric R; Minor, Mark A; Hollerbach, John M

2015-10-01

This paper presents the Treadport Active Wind Tunnel (TPAWT)-a full-body immersive virtual environment for the Treadport locomotion interface designed for generating wind on a user from any frontal direction at speeds up to 20 kph. The goal is to simulate the experience of realistic wind while walking in an outdoor virtual environment. A recirculating-type wind tunnel was created around the pre-existing Treadport installation by adding a large fan, ducting, and enclosure walls. Two sheets of air in a non-intrusive design flow along the side screens of the back-projection CAVE-like visual display, where they impinge and mix at the front screen to redirect towards the user in a full-body cross-section. By varying the flow conditions of the air sheets, the direction and speed of wind at the user are controlled. Design challenges to fit the wind tunnel in the pre-existing facility, and to manage turbulence to achieve stable and steerable flow, were overcome. The controller performance for wind speed and direction is demonstrated experimentally.

Remote visualization and scale analysis of large turbulence datatsets

NASA Astrophysics Data System (ADS)

Livescu, D.; Pulido, J.; Burns, R.; Canada, C.; Ahrens, J.; Hamann, B.

2015-12-01

Accurate simulations of turbulent flows require solving all the dynamically relevant scales of motions. This technique, called Direct Numerical Simulation, has been successfully applied to a variety of simple flows; however, the large-scale flows encountered in Geophysical Fluid Dynamics (GFD) would require meshes outside the range of the most powerful supercomputers for the foreseeable future. Nevertheless, the current generation of petascale computers has enabled unprecedented simulations of many types of turbulent flows which focus on various GFD aspects, from the idealized configurations extensively studied in the past to more complex flows closer to the practical applications. The pace at which such simulations are performed only continues to increase; however, the simulations themselves are restricted to a small number of groups with access to large computational platforms. Yet the petabytes of turbulence data offer almost limitless information on many different aspects of the flow, from the hierarchy of turbulence moments, spectra and correlations, to structure-functions, geometrical properties, etc. The ability to share such datasets with other groups can significantly reduce the time to analyze the data, help the creative process and increase the pace of discovery. Using the largest DOE supercomputing platforms, we have performed some of the biggest turbulence simulations to date, in various configurations, addressing specific aspects of turbulence production and mixing mechanisms. Until recently, the visualization and analysis of such datasets was restricted by access to large supercomputers. The public Johns Hopkins Turbulence database simplifies the access to multi-Terabyte turbulence datasets and facilitates turbulence analysis through the use of commodity hardware. First, one of our datasets, which is part of the database, will be described and then a framework that adds high-speed visualization and wavelet support for multi-resolution analysis of turbulence will be highlighted. The addition of wavelet support reduces the latency and bandwidth requirements for visualization, allowing for many concurrent users, and enables new types of analyses, including scale decomposition and coherent feature extraction.

Direct visualization of microalgae rupture by ultrasound-driven bubbles

NASA Astrophysics Data System (ADS)

Pommella, Angelo; Harun, Irina; Pouliopoulos, Antonis; Choi, James J.; Hellgardt, Klaus; Garbin, Valeria

2015-11-01

Cell rupture induced by ultrasound is central to applications in biotechnology. For instance, cell disruption is required in the production of biofuels from microalgae (unicellular species of algae). Ultrasound-induced cavitation, bubble collapse and jetting are exploited to induce sufficiently large viscous stresses to cause rupture of the cell membranes. It has recently been shown that seeding the flow with bubbles that act as cavitation nuclei significantly reduces the energy cost for cell processing. However, a fundamental understanding of the conditions for rupture of microalgae in the complex flow fields generated by ultrasound-driven bubbles is currently lacking. We perform high-speed video microscopy to visualize the miscroscale details of the interaction of Chlamydomonas reinhardtii , microalgae of about 10 μm in size, with ultrasound-driven microbubbles of 2-200 μm in diameter. We investigate the efficiency of cell rupture depending on ultrasound frequency and pressure amplitude (from 10 kPa up to 1 MPa), and the resulting bubble dynamics regimes. In particular we compare the efficiency of membrane rupture in the acoustic microstreaming flow induced by linear oscillations, with the case of violent bubble collapse and jetting. V.G. acknowledges partial support from the European Commission (FP7-PEOPLE-2013-CIG), Grant No. 618333.

Investigations of high-speed digital imaging of low-light-level events using pulsed near-infrared laser light sources

NASA Astrophysics Data System (ADS)

Jantzen, Connie; Slagle, Rick

1997-05-01

The distinction between exposure time and sample rate is often the first point raised in any discussion of high speed imaging. Many high speed events require exposure times considerably shorter than those that can be achieved solely by the sample rate of the camera, where exposure time equals 1/sample rate. Gating, a method of achieving short exposure times in digital cameras, is often difficult to achieve for exposure time requirements shorter than 100 microseconds. This paper discusses the advantages and limitations of using the short duration light pulse of a near infrared laser with high speed digital imaging systems. By closely matching the output wavelength of the pulsed laser to the peak near infrared response of current sensors, high speed image capture can be accomplished at very low (visible) light levels of illumination. By virtue of the short duration light pulse, adjustable to as short as two microseconds, image capture of very high speed events can be achieved at relatively low sample rates of less than 100 pictures per second, without image blur. For our initial investigations, we chose a ballistic subject. The results of early experimentation revealed the limitations of applying traditional ballistic imaging methods when using a pulsed infrared lightsource with a digital imaging system. These early disappointing results clarified the need to further identify the unique system characteristics of the digital imager and pulsed infrared combination. It was also necessary to investigate how the infrared reflectance and transmittance of common materials affects the imaging process. This experimental work yielded a surprising, successful methodology which will prove useful in imaging ballistic and weapons tests, as well as forensics, flow visualizations, spray pattern analyses, and nocturnal animal behavioral studies.

An experimental study of separated flow on a finite wing

NASA Technical Reports Server (NTRS)

Winkelmann, A. E.

1981-01-01

The flow field associated with the formation of a mushroom shaped trailing edge stall cell on a low-aspect-ratio (AR = 4.0) wing was investigated in a series of low speed wind tunnel tests (Reynolds number based on 15.2 cm chord = 480,000). Flow field surveys of the separation bubble and wake of a partially stalled and fully stalled wing were completed using a hot-wire probe, a split-film probe, and a directional sensitive pressure probe. A new color video display technique was developed to display the flow field survey data. Photographs were obtained of surface oil flow patterns and smoke flow visualization

An Experimental Investigation of Fluid Flow and Heating in Various Resonance Tube Modes

NASA Technical Reports Server (NTRS)

Sarohia, V.; Back, L. H.; Roschke, E. J.; Pathasarathy, S. P.

1976-01-01

Experiments have been performed to study resonance phenomena in tubes excited by underexpanded jet flows. This investigation comprised the following: Study of the various resonance tube modes under a wide range of nozzle pressure, spacing between nozzle and tube mouth, and different tube length; the effects of these modes on the endwall pressure and gas temperature; flow visualization of both jet and tube flows by spark shadowgraph technique; and measurement of wave speed inside the tube by the laser-schlieren techniques. An extensive study of the free-jet flow was undertaken to explain important aspects of various modes of operation of resonance tube flows.

Research methods of plasma stream interaction with heat-resistant materials

NASA Astrophysics Data System (ADS)

Tyuftyaev, A. S.; Gadzhiev, M. Kh; Sargsyan, M. A.; Chinnov, V. F.; Demirov, N. A.; Kavyrshin, D. I.; Ageev, A. G.; Khromov, M. A.

2016-11-01

An experimental automated system was designed and constructed for studying the parameters and characteristics of non-stationary interacting system high-enthalpy-plasma stream-investigated sample: enthalpy of plasma in the incident stream; speed and temperature of plasma stream; temperature of electrons and heavy particles, ionic composition and their spatial distribution; heat flux incident on the sample (kW/cm2); surface temperature of the sample; ablation of the sample material, and others. Measurements of achievable plasma heat flux levels are carried out by calorimetry of plasma streams incident on the surface of multisection copper calorimeter. Determination of acceleration characteristics for profiled plasma torch nozzle, as well as the gas flow rate is produced by measuring the total pressure using the Pitot tube. Video visualization of interacting system is carried out using synchronized high-speed cameras. Micropyrometry of the selected zone on the sample surface is carried out by high-speed, three-wavelength pyrometer. To measure the rate of mass loss of the sample, in addition to the weighing method of evaluation the methods of laser knife and two-position stereoscopy are used. Plasma and sample emission characteristics are performed with two separate spectrometers.

Low-speed Aerodynamic Investigations of a Hybrid Wing Body Configuration

NASA Technical Reports Server (NTRS)

Vicroy, Dan D.; Gatlin, Gregory M.; Jenkins, Luther N.; Murphy, Patrick C.; Carter, Melissa B.

2014-01-01

Two low-speed static wind tunnel tests and a water tunnel static and dynamic forced-motion test have been conducted on a hybrid wing-body (HWB) twinjet configuration. These tests, in addition to computational fluid dynamics (CFD) analysis, have provided a comprehensive dataset of the low-speed aerodynamic characteristics of this nonproprietary configuration. In addition to force and moment measurements, the tests included surface pressures, flow visualization, and off-body particle image velocimetry measurements. This paper will summarize the results of these tests and highlight the data that is available for code comparison or additional analysis.

Filtered Mass Density Function for Design Simulation of High Speed Airbreathing Propulsion Systems

NASA Technical Reports Server (NTRS)

Givi, P.; Madnia, C. K.; Gicquel, L. Y. M.; Sheikhi, M. R. H.; Drozda, T. G.

2002-01-01

The objective of this research is to improve and implement the filtered mass density function (FDF) methodology for large eddy simulation (LES) of high speed reacting turbulent flows. NASA is interested in the design of various components involved in air breathing propulsion systems such as the scramjet. There is a demand for development of robust tools that can aid in the design procedure. The physics of high speed reactive flows is rich with many complexities. LES is regarded as one of the most promising means of simulating turbulent reacting flows.

Assessment and application of Reynolds stress closure models to high-speed compressible flows

NASA Technical Reports Server (NTRS)

Gatski, T. B.; Sarkar, S.; Speziale, C. G.; Balakrishnan, L.; Abid, R.; Anderson, E. C.

1990-01-01

The paper presents results from the development of higher order closure models for the phenomological modeling of high-speed compressible flows. The work presented includes the introduction of an improved pressure-strain correlationi model applicable in both the low- and high-speed regime as well as modifications to the isotropic dissipation rate to account for dilatational effects. Finally, the question of stiffness commonly associated with the solution of two-equation and Reynolds stress transport equations in wall-bounded flows is examined and ways of relaxing these restrictions are discussed.

Flow interactions lead to orderly formations of flapping wings in forward flight

NASA Astrophysics Data System (ADS)

Ramananarivo, Sophie; Fang, Fang; Oza, Anand; Zhang, Jun; Ristroph, Leif

2016-11-01

Classic models of fish schools and flying formations of birds are built on the hypothesis that the preferred locations of an individual are determined by the flow left by its upstream neighbor. Lighthill posited that arrangements may in fact emerge passively from hydro- or aerodynamic interactions, drawing an analogy to the formation of crystals by intermolecular forces. Here, we carry out physical experiments aimed at testing the Lighthill conjecture and find that self-propelled flapping wings spontaneously assume one of multiple arrangements due to flow interactions. Wings in a tandem pair select the same forward speed, which tends to be faster than a single wing, while maintaining a separation distance that is an integer multiple of the wavelength traced out by each body. When perturbed, these locomotors robustly return to the same arrangement, and direct hydrodynamic force measurements reveal springlike restoring forces that maintain group cohesion. We also use these data to construct an interaction potential, showing how the observed positions of the follower correspond to stable wells in an energy landscape. Flow visualization and vortex-based theoretical models reveal coherent interactions in which the follower surfs on the periodic wake left by the leader. These results indicate that, for the high-Reynolds-number flows characteristic of schools and flocks, collective locomotion at enhanced speed and in orderly formations can emerge from flow interactions alone. If true for larger groups, then the view of collectives as ordered states of matter may prove to be a useful analogy.

The numerical simulation of a high-speed axial flow compressor

NASA Technical Reports Server (NTRS)

Mulac, Richard A.; Adamczyk, John J.

1991-01-01

The advancement of high-speed axial-flow multistage compressors is impeded by a lack of detailed flow-field information. Recent development in compressor flow modeling and numerical simulation have the potential to provide needed information in a timely manner. The development of a computer program is described to solve the viscous form of the average-passage equation system for multistage turbomachinery. Programming issues such as in-core versus out-of-core data storage and CPU utilization (parallelization, vectorization, and chaining) are addressed. Code performance is evaluated through the simulation of the first four stages of a five-stage, high-speed, axial-flow compressor. The second part addresses the flow physics which can be obtained from the numerical simulation. In particular, an examination of the endwall flow structure is made, and its impact on blockage distribution assessed.

Combustor flame flashback

NASA Technical Reports Server (NTRS)

Proctor, M. P.; Tien, J. S.

1985-01-01

A stainless steel, two-dimensional (rectangular), center-dump, premixed-prevaporized combustor with quartz window sidewalls for visual access was designed, built, and used to study flashback. A parametric study revealed that the flashback equivalence ratio decreased slightly as the inlet air temperature increased. It also indicated that the average premixer velocity and premixer wall temperature were not governing parameters of flashback. The steady-state velocity balance concept as the flashback mechanism was not supported. From visual observation several stages of burning were identified. High speed photography verified upstream flame propagation with the leading edge of the flame front near the premixer wall. Combustion instabilities (spontaneous pressure oscillations) were discovered during combustion at the dump plane and during flashback. The pressure oscillation frequency ranged from 40 to 80 Hz. The peak-to-peak amplitude (up to 1.4 psi) increased as the fuel/air equivalence ratio was increased attaining a maximum value just before flashback. The amplitude suddenly decreased when the flame stabilized in the premixer. The pressure oscillations were large enough to cause a local flow reversal. A simple test using ceramic fiber tufts indicated flow reversals existed at the premixer exit during flickering. It is suspected that flashback occurs through the premixer wall boundary layer flow reversal caused by combustion instability. A theoretical analysis of periodic flow in the premixing channel has been made. The theory supports the flow reversal mechanism.

Characterization of flow in a scroll duct

NASA Technical Reports Server (NTRS)

Begg, E. K.; Bennett, J. C.

1985-01-01

A quantitative, flow visualization study was made of a partially elliptic cross section, inward curving duct (scroll duct), with an axial outflow through a vaneless annular cutlet. The working fluid was water, with a Re(d) of 40,000 at the inlet to the scroll duct, this Reynolds number being representative of the conditions in an actual gas turbine scroll. Both still and high speed moving pictures of fluorescein dye injected into the flow and illuminated by an argon ion laser were used to document the flow. Strong secondary flow, similar to the secondary flow in a pipe bend, was found in the bottom half of the scroll within the first 180 degs of turning. The pressure field set up by the turning duct was strong enough to affect the inlet flow condition. At 90 degs downstream, the large scale secondary flow was found to be oscillatory in nature. The exit flow was nonuniform in the annular exit. By 270 degs downstream, the flow appeared unorganized with no distinctive secondary flow pattern. Large scale structures from the upstream core region appeared by 90 degs and continued through the duct to reenter at the inlet section.

Exploratory flow visualization investigation of mast-mounted sights in presence of a rotor

NASA Technical Reports Server (NTRS)

Ghee, Terence A.; Kelley, Henry L.

1995-01-01

A flow visualization investigation with a laser light sheet system was conducted on a 27-percent-scale AH-64 attack helicopter model fitted with two mast-mounted sights in the langley 14- by 22-foot subsonic tunnel. The investigation was conducted to identify aerodynamic phenomena that may have contributed to adverse vibration encountered during full-scale flight of the AH-64D apache/longbow helicopter with an asymmetric mast-mounted sight. Symmetric and asymmetric mast-mounted sights oriented at several skew angles were tested at simulated forward and rearward flight speeds of 30 and 45 knots. A laser light sheet system was used to visualize the flow in planes parallel to and perpendicular to the free-stream flow. Analysis of these flow visualization data identified frequencies of flow patterns in the wake shed from the sight, the streamline angle at the sight, and the location where the shed wake crossed the rotor plane. Differences in wake structure were observed between the sight configurations and various skew angles. Analysis of lateral light sheet plane data implied significant vortex structure in the wake of the asymmetric mast-mounted sight in the configuration that produced maximum in-flight vibration. The data showed no significant vortex structure in the wake of the asymmetric and symmetric configurations that produced no increase in in-flight adverse vibration.

Laryngeal High-Speed Videoendoscopy: Rationale and Recommendation for Accurate and Consistent Terminology

ERIC Educational Resources Information Center

Deliyski, Dimitar D.; Hillman, Robert E.; Mehta, Daryush D.

2015-01-01

Purpose: The authors discuss the rationale behind the term "laryngeal high-speed videoendoscopy" to describe the application of high-speed endoscopic imaging techniques to the visualization of vocal fold vibration. Method: Commentary on the advantages of using accurate and consistent terminology in the field of voice research is…

Study of Properties of the Microwave Streamer Discharge in a High-Speed Flow of Gas and in Two-Phase Medium

DTIC Science & Technology

2006-08-01

comparably high pressure p only at p Torr. This is connected with technical limitations of comparably high power PMW generation even with a help of...ignited in a high -speed air flow with vfl = 5⋅104 cm/ s . A scheme of the experimental setup with EM beam with λ = 2.5 cm in this configuration is...corresponding diagram in Fig.5.9.4.1. One can see from it that a high -speed air flow existed during τfl = 1 s in experiments. t=0 t=1 s t=0.2 s t

Novel full‐spectral flow cytometry with multiple spectrally‐adjacent fluorescent proteins and fluorochromes and visualization of in vivo cellular movement

PubMed Central

Futamura, Koji; Sekino, Masashi; Hata, Akihiro; Ikebuchi, Ryoyo; Nakanishi, Yasutaka; Egawa, Gyohei; Kabashima, Kenji; Watanabe, Takeshi; Furuki, Motohiro

2015-01-01

Abstract Flow cytometric analysis with multicolor fluoroprobes is an essential method for detecting biological signatures of cells. Here, we present a new full‐spectral flow cytometer (spectral‐FCM). Unlike conventional flow cytometer, this spectral‐FCM acquires the emitted fluorescence for all probes across the full‐spectrum from each cell with 32 channels sequential PMT unit after dispersion with prism, and extracts the signals of each fluoroprobe based on the spectral shape of each fluoroprobe using unique algorithm in high speed, high sensitive, accurate, automatic and real‐time. The spectral‐FCM detects the continuous changes in emission spectra from green to red of the photoconvertible protein, KikGR with high‐spectral resolution and separates spectrally‐adjacent fluoroprobes, such as FITC (Emission peak (Em) 519 nm) and EGFP (Em 507 nm). Moreover, the spectral‐FCM can measure and subtract autofluorescence of each cell providing increased signal‐to‐noise ratios and improved resolution of dim samples, which leads to a transformative technology for investigation of single cell state and function. These advances make it possible to perform 11‐color fluorescence analysis to visualize movement of multilinage immune cells by using KikGR‐expressing mice. Thus, the novel spectral flow cytometry improves the combinational use of spectrally‐adjacent various FPs and multicolor fluorochromes in metabolically active cell for the investigation of not only the immune system but also other research and clinical fields of use. © 2015 The Authors. Cytometry Part A Published by Wiley Periodicals, Inc. on behalf of ISAC PMID:26217952

The effect of dry spots on heat transfer in a locally heated liquid film moving under the action of gas flow in a channel

NASA Astrophysics Data System (ADS)

Zaitsev, D. V.; Tkachenko, E. M.; Bykovskaya, E. F.

2017-11-01

Intensive evaporation of a thin liquid film, moving in a flat micro-/minichannel under the action of gas flow is very promising for the use in cooling systems of modern semiconductor devices with localized heat sources of high intensity. In this work, using the high-speed visualization, the effect of the formation of dry spots on heat transfer in a locally heated liquid film shear-driven in a channel was investigated. It was found that the maximum intensity of heat removal from the heater is achieved in the mode, when the film flow continuity is broken. During the experiment the total area of dry spots increases with increasing heat flux and heater temperature, but when the heater reaches a certain temperature (≈100°C), the total area begins to decrease. However, the length of contact line increases with increasing heat flux and reaches a maximum in the pre-crisis regime. Intensive evaporation in the region of the contact line may explain the achievement of high heat fluxes in the shear-driven liquid film.

Effect of surface roughness on the heating rates of large-angled hypersonic blunt cones

NASA Astrophysics Data System (ADS)

Irimpan, Kiran Joy; Menezes, Viren

2018-03-01

Surface-roughness caused by the residue of an ablative Thermal Protection System (TPS) can alter the turbulence level and surface heating rates on a hypersonic re-entry capsule. Large-scale surface-roughness that could represent an ablated TPS, was introduced over the forebody of a 120° apex angle blunt cone, in order to test for its influence on surface heating rates in a hypersonic freestream of Mach 8.8. The surface heat transfer rates measured on smooth and roughened models under the same freestream conditions were compared. The hypersonic flow-fields of the smooth and rough-surfaced models were visualized to analyse the flow physics. Qualitative numerical simulations and pressure measurements were carried out to have an insight into the high-speed flow physics. Experimental observations under moderate Reynolds numbers indicated a delayed transition and an overall reduction of 17-46% in surface heating rates on the roughened model.

Characterization of Ventilatory Modes in Dragonfly Nymph

NASA Astrophysics Data System (ADS)

Roh, Chris; Saxton-Fox, Theresa; Gharib, Morteza

2013-11-01

A dragonfly nymph's highly modified hindgut has multiple ventilatory modes: hyperventilation (i.e. jet propulsion), gulping ventilation (extended expiratory phase) and normal ventilation. Each mode involves dynamic manipulation of the exit diameter and pressure. To study the different fluid dynamics associated with the three modes, Anisopteran larvae of the family Aeshnidae were tethered onto a rod for flow visualization. The result showed distinct flow structures. The hyperventilation showed a highly turbulent and powerful jet that occurred at high frequency. The gulping ventilation produced a single vortex at a moderate frequency. The normal ventilation showed two distinct vortices, a low-Reynolds number vortex, followed by a high-Reynolds number vortex. Furthermore, a correlation of the formation of the vortices with the movement of the sternum showed that the dragonfly is actively controlling the timing and the speed of the vortices to have them at equal distance from the jet exit at the onset of inspiration. This behavior prevents inspiration of the oxygen deficient expirated water, resulting in the maximization of the oxygen intake. Supported by NSF GRFP.

Navier-Stokes Simulation of UH-60A Rotor/Wake Interaction Using Adaptive Mesh Refinement

NASA Technical Reports Server (NTRS)

Chaderjian, Neal M.

2017-01-01

Time-dependent Navier-Stokes simulations have been carried out for a flexible UH-60A rotor in forward flight, where the rotor wake interacts with the rotor blades. These flow conditions involved blade vortex interaction and dynamic stall, two common conditions that occur as modern helicopter designs strive to achieve greater flight speeds and payload capacity. These numerical simulations utilized high-order spatial accuracy and delayed detached eddy simulation. Emphasis was placed on understanding how improved rotor wake resolution affects the prediction of the normal force, pitching moment, and chord force of the rotor. Adaptive mesh refinement was used to highly resolve the turbulent rotor wake in a computationally efficient manner. Moreover, blade vortex interaction was found to trigger dynamic stall. Time-dependent flow visualization was utilized to provide an improved understanding of the numerical and physical mechanisms involved with three-dimensional dynamic stall.

Intermittent large amplitude internal waves observed in Port Susan, Puget Sound

NASA Astrophysics Data System (ADS)

Harris, J. C.; Decker, L.

2017-07-01

A previously unreported internal tidal bore, which evolves into solitary internal wave packets, was observed in Port Susan, Puget Sound, and the timing, speed, and amplitude of the waves were measured by CTD and visual observation. Acoustic Doppler current profiler (ADCP) measurements were attempted, but unsuccessful. The waves appear to be generated with the ebb flow along the tidal flats of the Stillaguamish River, and the speed and width of the resulting waves can be predicted from second-order KdV theory. Their eventual dissipation may contribute significantly to surface mixing locally, particularly in comparison with the local dissipation due to the tides. Visually the waves appear in fair weather as a strong foam front, which is less visible the farther they propagate.

Experimental and computational investigation of the NASA low-speed centrifugal compressor flow field

NASA Technical Reports Server (NTRS)

Hathaway, Michael D.; Chriss, Randall M.; Wood, Jerry R.; Strazisar, Anthony J.

1993-01-01

An experimental and computational investigation of the NASA Lewis Research Center's low-speed centrifugal compressor (LSCC) flow field was conducted using laser anemometry and Dawes' three-dimensional viscous code. The experimental configuration consisted of a backswept impeller followed by a vaneless diffuser. Measurements of the three-dimensional velocity field were acquired at several measurement planes through the compressor. The measurements describe both the throughflow and secondary velocity field along each measurement plane. In several cases the measurements provide details of the flow within the blade boundary layers. Insight into the complex flow physics within centrifugal compressors is provided by the computational fluid dynamics analysis (CFD), and assessment of the CFD predictions is provided by comparison with the measurements. Five-hole probe and hot-wire surveys at the inlet and exit to the impeller as well as surface flow visualization along the impeller blade surfaces provided independent confirmation of the laser measurement technique. The results clearly document the development of the throughflow velocity wake that is characteristic of unshrouded centrifugal compressors.

The Langley 14- by 22-Foot Subsonic Tunnel: Description, Flow Characteristics, and Guide for Users

NASA Technical Reports Server (NTRS)

Gentry, Garl L., Jr.; Quinto, P. Frank; Gatlin, Gregory M.; Applin, Zachary T.

1990-01-01

The Langley 14- by 22-foot Subsonic Tunnel is a closed circuit, single-return atmospheric wind tunnel with a test section that can be operated in a variety of configurations (closed, slotted, partially open, and open). The closed test section configuration is 14.5 ft high by 21.75 ft wide and 50 ft long with a maximum speed of about 338 ft/sec. The open test section configuration has a maximum speed of about 270 ft/sec, and is formed by raising the ceiling and walls, to form a floor-only configuration. The tunnel may be configured with a moving-belt ground plane and a floor boundary-layer removal system at the entrance to the test section for ground effect testing. In addition, the tunnel had a two-component laser velocimeter, a frequency modulated (FM) tape system for dynamic data acquisition, flow visualization equipment, and acoustic testing capabilities. Users of the 14- by 22-foot Subsonic Tunnel are provided with information required for planning of experimental investigations including test hardware and model support systems.

Flight validation of a pulsed smoke flow visualization system

NASA Technical Reports Server (NTRS)

Ward, Donald T.; Dorsett, Kenneth M.

1993-01-01

A flow visualization scheme, designed to measure vortex fluid dynamics on research aircraft, was validated in flight. Strake vortex trajectories and axial core velocities were determined using pulsed smoke, high-speed video images, and semiautomated image edge detection hardware and software. Smoke was pulsed by using a fast-acting three-way valve. After being redesigned because of repeatedly jamming in flight, the valve shuttle operated flawlessly during the last two tests. A 25-percent scale, Gothic strake was used to generate vortex over the wing of a GA-7 Cougar and was operated at a local angle of attack of 22 degrees and Reynolds number of approximately 7.8 x 10(exp 5)/ft. Maximum axial velocities measured in the vortex core were between 1.75 and 1.95 times the freestream velocity. Analysis of the pulsed smoke system's affect on forebody vortices indicates that the system may reorient the forebody vortex system; however, blowing momentum coefficients normally used will have no appreciable affect on the leading-edge extension vortex system. It is recommended that a similar pulsed smoke system be installed on the F/A-18 High Angle Research Vehicle and that this approach be used to analyze vortex core dynamics during the remainder of its high-angle-of-attack research flights.

Turbulent flow reduces oxygen consumption in the labriform swimming shiner perch, Cymatogaster aggregata.

PubMed

van der Hoop, Julie M; Byron, Margaret L; Ozolina, Karlina; Miller, David L; Johansen, Jacob L; Domenici, Paolo; Steffensen, John F

2018-06-12

Fish swimming energetics are often measured in laboratory environments which attempt to minimize turbulence, though turbulent flows are common in the natural environment. To test whether the swimming energetics and kinematics of shiner perch, Cymatogaster aggregata (a labriform swimmer), were affected by turbulence, two flow conditions were constructed in a swim-tunnel respirometer. A low-turbulence flow was created using a common swim-tunnel respirometry setup with a flow straightener and fine-mesh grid to minimize velocity fluctuations. A high-turbulence flow condition was created by allowing large velocity fluctuations to persist without a flow straightener or fine grid. The two conditions were tested with particle image velocimetry to confirm significantly different turbulence properties throughout a range of mean flow speeds. Oxygen consumption rate of the swimming fish increased with swimming speed and pectoral fin beat frequency in both flow conditions. Higher turbulence also caused a greater positional variability in swimming individuals (versus low-turbulence flow) at medium and high speeds. Surprisingly, fish used less oxygen in high-turbulence compared with low-turbulence flow at medium and high swimming speeds. Simultaneous measurements of swimming kinematics indicated that these reductions in oxygen consumption could not be explained by specific known flow-adaptive behaviours such as Kármán gaiting or entraining. Therefore, fish in high-turbulence flow may take advantage of the high variability in turbulent energy through time. These results suggest that swimming behaviour and energetics measured in the lab in straightened flow, typical of standard swimming respirometers, might differ from that of more turbulent, semi-natural flow conditions. © 2018. Published by The Company of Biologists Ltd.

In vivo flow speed measurement of capillaries by photoacoustic correlation spectroscopy.

PubMed

Chen, Sung-Liang; Xie, Zhixing; Carson, Paul L; Wang, Xueding; Guo, L Jay

2011-10-15

We recently proposed photoacoustic correlation spectroscopy (PACS) and demonstrated a proof-of-concept experiment. Here we use the technique for in vivo flow speed measurement in capillaries in a chick embryo model. The photoacoustic microscopy system is used to render high spatial resolution and high sensitivity, enabling sufficient signals from single red blood cells. The probe beam size is calibrated by a blood-mimicking phantom. The results indicate the feasibility of using PACS to study flow speeds in capillaries.

High-repetition-rate interferometric Rayleigh scattering for flow-velocity measurements

NASA Astrophysics Data System (ADS)

Estevadeordal, Jordi; Jiang, Naibo; Cutler, Andrew D.; Felver, Josef J.; Slipchenko, Mikhail N.; Danehy, Paul M.; Gord, James R.; Roy, Sukesh

2018-03-01

High-repetition-rate interferometric-Rayleigh-scattering (IRS) velocimetry is demonstrated for non-intrusive, high-speed flow-velocity measurements. High temporal resolution is obtained with a quasi-continuous burst-mode laser that is capable of operating at 10-100 kHz, providing 10-ms bursts with pulse widths of 5-1000 ns and pulse energy > 100 mJ at 532 nm. Coupled with a high-speed camera system, the IRS method is based on imaging the flow field through an etalon with 8-GHz free spectral range and capturing the Doppler shift of the Rayleigh-scattered light from the flow at multiple points having constructive interference. The seed-laser linewidth permits a laser linewidth of < 150 MHz at 532 nm. The technique is demonstrated in a high-speed jet, and high-repetition-rate image sequences are shown.

The flip-flop nozzle extended to supersonic flows

NASA Technical Reports Server (NTRS)

Raman, Ganesh; Hailye, Michael; Rice, Edward J.

1992-01-01

An experiment studying a fluidically oscillated rectangular jet flow was conducted. The Mach number was varied over a range from low subsonic to supersonic. Unsteady velocity and pressure measurements were made using hot wires and piezoresistive pressure transducers. In addition smoke flow visualization using high speed photography was used to document the oscillation of the jet. For the subsonic flip-flop jet it was found that the apparent time-mean widening of the jet was not accompanied by an increase in mass flux. It was found that it is possible to extend the operation of these devices to supersonic flows. Most of the measurements were made for a fixed nozzle geometry for which the oscillations ceased at a fully expanded Mach number of 1.58. By varying the nozzle geometry this limitation was overcome and operation was extended to Mach 1.8. The streamwise velocity perturbation levels produced by this device were much higher than the perturbation levels that could be produced using conventional excitation sources such as acoustic drivers. In view of this ability to produce high amplitudes, the potential for using small scale fluidically oscillated jet as an unsteady excitation source for the control of shear flows in full scale practical applications seems promising.

The flip flop nozzle extended to supersonic flows

NASA Technical Reports Server (NTRS)

Raman, Ganesh; Hailye, Michael; Rice, Edward J.

1992-01-01

An experiment studying a fluidically oscillated rectangular jet flow was conducted. The Mach number was varied over a range from low subsonic to supersonic. Unsteady velocity and pressure measurements were made using hot wires and piezoresistive pressure transducers. In addition smoke flow visualization using high speed photography was used to document the oscillation of the jet. For the subsonic flip-flop jet it was found that the apparent time-mean widening of the jet was not accompanied by an increase in mass flux. It was found that it is possible to extend the operation of these devices to supersonic flows. Most of the measurements were made for a fixed nozzle geometry for which the oscillations ceased at a fully expanded Mach number of 1.58. By varying the nozzle geometry this limitation was overcome and operation was extended to Mach 1.8. The streamwise velocity perturbation levels produced by this device were much higher than the perturbation levels that could be produced using conventional excitation sources such as acoustic drivers. In view of this ability to produce high amplitudes, the potential for using small scale fluidically oscillated jet as an unsteady excitation source for the control of shear flows in full scale practical applications seems promising.

The temperature of unheated bodies in a high-speed gas stream

NASA Technical Reports Server (NTRS)

Eckert, E; Weise, W

1941-01-01

The present report deals with temperature measurements on cylinders of 0.2 to 3 millimeters diameter in longitudinal and transverse air flow at speeds of 100 to 300 meters per second. Within the explored test range, that is, the probable laminar boundary layer region, the temperature of the cylinders in axial flow is practically independent of the speed and in good agreement with Pohlhausen's theoretical values; Whereas, in transverse flow, cylinders of certain diameter manifest a close relationship with speed, the ratio of the temperature above the air of the body to the adiabatic stagnation temperature decreases with rising speed and then rises again from a Mach number of 0.6. The importance of this "specific temperature" of the body for heat-transfer studies at high speed is discussed.

Wind Tunnel Investigation of the Effects of Surface Porosity and Vertical Tail Placement on Slender Wing Vortex Flow Aerodynamics at Supersonic Speeds

NASA Technical Reports Server (NTRS)

Erickson, Gary E.

2007-01-01

A wind tunnel experiment was conducted in the NASA Langley Research Center (LaRC) Unitary Plan Wind Tunnel (UPWT) to determine the effects of passive surface porosity and vertical tail placement on vortex flow development and interactions about a general research fighter configuration at supersonic speeds. Optical flow measurement and flow visualization techniques were used that featured pressure sensitive paint (PSP), laser vapor screen (LVS), and schlieren, These techniques were combined with conventional electronically-scanned pressure (ESP) and six-component force and moment measurements to quantify and to visualize the effects of flow-through porosity applied to a wing leading edge extension (LEX) and the placement of centerline and twin vertical tails on the vortex-dominated flow field of a 65 cropped delta wing model. Test results were obtained at free-stream Mach numbers of 1.6, 1.8, and 2.1 and a Reynolds number per foot of 2.0 million. LEX porosity promoted a wing vortex-dominated flow field as a result of a diffusion and weakening of the LEX vortex. The redistribution of the vortex-induced suction pressures contributed to large nose-down pitching moment increments but did not significantly affect the vortex-induced lift. The trends associated with LEX porosity were unaffected by vertical tail placement. The centerline tail configuration generally provided more stable rolling moments and yawing moments compared to the twin wing-mounted vertical tails. The strength of a complex system of shock waves between the twin tails was reduced by LEX porosity.

Effective solidity in vertical axis wind turbines

NASA Astrophysics Data System (ADS)

Parker, Colin M.; Leftwich, Megan C.

2016-11-01

The flow surrounding vertical axis wind turbines (VAWTs) is investigated using particle imaging velocimetry (PIV). This is done in a low-speed wind tunnel with a scale model that closely matches geometric and dynamic properties tip-speed ratio and Reynolds number of a full size turbine. Previous results have shown a strong dependance on the tip-speed ratio on the wake structure of the spinning turbine. However, it is not clear whether this is a speed or solidity effect. To determine this, we have measured the wakes of three turbines with different chord-to-diameter ratios, and a solid cylinder. The flow is visualized at the horizontal mid-plane as well as the vertical mid-plane behind the turbine. The results are both ensemble averaged and phase averaged by syncing the PIV system with the rotation of the turbine. By keeping the Reynolds number constant with both chord and diameter, we can determine how each effects the wake structure. As these parameters are varied there are distinct changes in the mean flow of the wake. Additionally, by looking at the vorticity in the phase averaged profiles we can see structural changes to the overall wake pattern.

A high sensitivity 20Mfps CMOS image sensor with readout speed of 1Tpixel/sec for visualization of ultra-high speed phenomena

NASA Astrophysics Data System (ADS)

Kuroda, R.; Sugawa, S.

2017-02-01

Ultra-high speed (UHS) CMOS image sensors with on-chop analog memories placed on the periphery of pixel array for the visualization of UHS phenomena are overviewed in this paper. The developed UHS CMOS image sensors consist of 400H×256V pixels and 128 memories/pixel, and the readout speed of 1Tpixel/sec is obtained, leading to 10 Mfps full resolution video capturing with consecutive 128 frames, and 20 Mfps half resolution video capturing with consecutive 256 frames. The first development model has been employed in the high speed video camera and put in practical use in 2012. By the development of dedicated process technologies, photosensitivity improvement and power consumption reduction were simultaneously achieved, and the performance improved version has been utilized in the commercialized high-speed video camera since 2015 that offers 10 Mfps with ISO16,000 photosensitivity. Due to the improved photosensitivity, clear images can be captured and analyzed even under low light condition, such as under a microscope as well as capturing of UHS light emission phenomena.

Flowfield measurements in a separated and reattached flat plate turbulent boundary layer

NASA Technical Reports Server (NTRS)

Patrick, William P.

1987-01-01

The separation and reattachment of a large-scale, two-dimensional turbulent boundary layer at low subsonic speed on a flat plate has been studied experimentally. The separation bubble was 55 cm long and had a maximum bubble thickness, measured to the height of the mean dividing streamline, of 17 cm, which was twice the thickness of the inlet boundary layer. A combination of laser velocimetry, hot-wire anemometry, pneumatic probing techniques, and flow visualization were used as diagnostics. Principal findings were that an outer inviscid rotational flow was defined which essentially convected over the blockage associated with the inner, viscously dominated bubble recirculation region. A strong backflow region in which the flow moved upstream 100 percent of the time was measured near the test surface over the central 35 percent of the bubble. A laminar backflow boundary layer having pseudo-turbulent characteristics including a log-linear velocity profile was generated under the highly turbulent backflow. Velocity profile shapes in the reversed flow region matched a previously developed universal backflow profile at the upstream edge of the separation region but not in the steady backflow region downstream. A smoke flow visualization movie and hot-film measurements revealed low frequency nonperiodic flapping at reattachment. However, forward flow fraction data at reattachment and mean velocity profiles in the redeveloping boundary layer downstream of reattachment correlated with backward-facing step data when the axial dimension was scaled by the distance from the maximum bubble thickness to reattachment.

DFLOWZ: A free program to evaluate the area potentially inundated by a debris flow

NASA Astrophysics Data System (ADS)

Berti, M.; Simoni, A.

2014-06-01

The transport and deposition mechanisms of debris flows are still poorly understood due to the complexity of the interactions governing the behavior of water-sediment mixtures. Empirical-statistical methods can therefore be used, instead of more sophisticated numerical methods, to predict the depositional behavior of these highly dangerous gravitational movements. We use widely accepted semi-empirical scaling relations and propose an automated procedure (DFLOWZ) to estimate the area potentially inundated by a debris flow event. Beside a digital elevation model (DEM), the procedure has only two input requirements: the debris flow volume and the possible flow-path. The procedure is implemented in Matlab and a Graphical User Interface helps to visualize initial conditions, flow propagation and final results. Different hypothesis about the depositional behavior of an event can be tested together with the possible effect of simple remedial measures. Uncertainties associated to scaling relations can be treated and their impact on results evaluated. Our freeware application aims to facilitate and speed up the process of susceptibility mapping. We discuss limits and advantages of the method in order to inform inexperienced users.

Label-free and highly sensitive optical imaging of detailed microcirculation within meninges and cortex in mice with the cranium left intact

NASA Astrophysics Data System (ADS)

Jia, Yali; An, Lin; Wang, Ruikang K.

2010-05-01

We demonstrate for the first time that the detailed blood flow distribution within intracranial dura mater and cortex can be visualized by an ultrahigh sensitive optical microangiography (UHS-OMAG). The study uses an UHS-OMAG system operating at 1310 nm with an imaging speed at 150 frames per second that requires ~10 s to complete one 3-D scan of ~2.5×2.5 mm2. The system is sensitive to blood flow with a velocity ranging from ~4 μm/s to ~23 mm/s. We show superior performance of UHS-OMAG in providing functional images of capillary level microcirculation within meninges in mice with the cranium left intact, the results of which correlate well with the standard dural histopathology.

A processing work-flow for measuring erythrocytes velocity in extended vascular networks from wide field high-resolution optical imaging data.

PubMed

Deneux, Thomas; Takerkart, Sylvain; Grinvald, Amiram; Masson, Guillaume S; Vanzetta, Ivo

2012-02-01

Comprehensive information on the spatio-temporal dynamics of the vascular response is needed to underpin the signals used in hemodynamics-based functional imaging. It has recently been shown that red blood cells (RBCs) velocity and its changes can be extracted from wide-field optical imaging recordings of intrinsic absorption changes in cortex. Here, we describe a complete processing work-flow for reliable RBC velocity estimation in cortical networks. Several pre-processing steps are implemented: image co-registration, necessary to correct for small movements of the vasculature, semi-automatic image segmentation for fast and reproducible vessel selection, reconstruction of RBC trajectories patterns for each micro-vessel, and spatio-temporal filtering to enhance the desired data characteristics. The main analysis step is composed of two robust algorithms for estimating the RBCs' velocity field. Vessel diameter and its changes are also estimated, as well as local changes in backscattered light intensity. This full processing chain is implemented with a software suite that is freely distributed. The software uses efficient data management for handling the very large data sets obtained with in vivo optical imaging. It offers a complete and user-friendly graphical user interface with visualization tools for displaying and exploring data and results. A full data simulation framework is also provided in order to optimize the performances of the algorithm with respect to several characteristics of the data. We illustrate the performance of our method in three different cases of in vivo data. We first document the massive RBC speed response evoked by a spreading depression in anesthetized rat somato-sensory cortex. Second, we show the velocity response elicited by a visual stimulation in anesthetized cat visual cortex. Finally, we report, for the first time, visually-evoked RBC speed responses in an extended vascular network in awake monkey extrastriate cortex. Copyright © 2011 Elsevier Inc. All rights reserved.

In-flight total forces, moments and static aeroelastic characteristics of an oblique-wing research airplane

NASA Technical Reports Server (NTRS)

Curry, R. E.; Sim, A. G.

1984-01-01

A low-speed flight investigation has provided total force and moment coefficients and aeroelastic effects for the AD-1 oblique-wing research airplane. The results were interpreted and compared with predictions that were based on wind tunnel data. An assessment has been made of the aeroelastic wing bending design criteria. Lateral-directional trim requirements caused by asymmetry were determined. At angles of attack near stall, flow visualization indicated viscous flow separation and spanwise vortex flow. These effects were also apparent in the force and moment data.

Experimental Study of Tip Vortex Flow from a Periodically Pitched Airfoil Section

NASA Technical Reports Server (NTRS)

Zaman, Khairul; Fagan, Amy; Mankbadi, Mina

2016-01-01

An experimental investigation of tip vortex flow from a NACA0012 airfoil, pitched periodically at various frequencies, is conducted in a low-speed wind tunnel. Initially, data for stationary airfoil held fixed at various angles-of-attack are gathered. Flow visualization pictures as well as detailed cross-sectional properties areobtained at various streamwise locations using hot-wire anemometry. Data include mean velocity, streamwise vorticity as well as various turbulent stresses. Preliminary data are also acquired for periodically pitched airfoil. These results are briefly presented in this extended abstract.

Control of self-motion in dynamic fluids: fish do it differently from bees.

PubMed

Scholtyssek, Christine; Dacke, Marie; Kröger, Ronald; Baird, Emily

2014-05-01

To detect and avoid collisions, animals need to perceive and control the distance and the speed with which they are moving relative to obstacles. This is especially challenging for swimming and flying animals that must control movement in a dynamic fluid without reference from physical contact to the ground. Flying animals primarily rely on optic flow to control flight speed and distance to obstacles. Here, we investigate whether swimming animals use similar strategies for self-motion control to flying animals by directly comparing the trajectories of zebrafish (Danio rerio) and bumblebees (Bombus terrestris) moving through the same experimental tunnel. While moving through the tunnel, black and white patterns produced (i) strong horizontal optic flow cues on both walls, (ii) weak horizontal optic flow cues on both walls and (iii) strong optic flow cues on one wall and weak optic flow cues on the other. We find that the mean speed of zebrafish does not depend on the amount of optic flow perceived from the walls. We further show that zebrafish, unlike bumblebees, move closer to the wall that provides the strongest visual feedback. This unexpected preference for strong optic flow cues may reflect an adaptation for self-motion control in water or in environments where visibility is limited. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Experimental Investigation of the Low-Speed Aerodynamic Characteristics of a 5.8-Percent Scale Hybrid Wing Body Configuration

NASA Technical Reports Server (NTRS)

Gatlin, Gregory M.; Vicroy, Dan D.; Carter, Melissa B.

2012-01-01

A low-speed experimental investigation has been conducted on a 5.8-percent scale Hybrid Wing Body configuration in the NASA Langley 14- by 22-Foot Subsonic Tunnel. This Hybrid Wing Body (HWB) configuration was designed with specific intention to support the NASA Environmentally Responsible Aviation (ERA) Project goals of reduced noise, emissions, and fuel burn. This HWB configuration incorporates twin, podded nacelles mounted on the vehicle upper surface between twin vertical tails. Low-speed aerodynamic characteristics were assessed through the acquisition of force and moment, surface pressure, and flow visualization data. Longitudinal and lateral-directional characteristics were investigated on this multi-component model. The effects of a drooped leading edge, longitudinal flow-through nacelle location, vertical tail shape and position, elevon deflection, and rudder deflection have been studied. The basic configuration aerodynamics, as well as the effects of these configuration variations, are presented in this paper.

Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows

NASA Technical Reports Server (NTRS)

Givi, Peyman; Madnia, C. K.; Steinberger, C. J.; Tsai, A.

1991-01-01

This research is involved with the implementations of advanced computational schemes based on large eddy simulations (LES) and direct numerical simulations (DNS) to study the phenomenon of mixing and its coupling with chemical reactions in compressible turbulent flows. In the efforts related to LES, a research program was initiated to extend the present capabilities of this method for the treatment of chemically reacting flows, whereas in the DNS efforts, focus was on detailed investigations of the effects of compressibility, heat release, and nonequilibrium kinetics modeling in high speed reacting flows. The efforts to date were primarily focussed on simulations of simple flows, namely, homogeneous compressible flows and temporally developing hign speed mixing layers. A summary of the accomplishments is provided.

Altitude-Wind-Tunnel Investigation of a 4000-Pound-Thrust Axial-Flow Turbojet Engine. II - Operational Characteristics. II; Operational Characteristics

NASA Technical Reports Server (NTRS)

Fleming, William A.

1948-01-01

An investigation was conducted in the Cleveland altitude wind tunnel to determine the operational characteristics of an axial flow-type turbojet engine with a 4000-pound-thrust rating over a range of pressure altitudes from 5,000 to 50,OOO feet, ram pressure ratios from 1.00 to 1.86, and temperatures from 60 deg to -50 deg F. The low-flow (standard) compressor with which the engine was originally equipped was replaced by a high-flow compressor for part of the investigation. The effects of altitude and airspeed on such operating characteristics as operating range, stability of combustion, acceleration, starting, operation of fuel-control systems, and bearing cooling were investigated. With the low-flow compressor, the engine could be operated at full speed without serious burner unbalance at altitudes up to 50,000 feet. Increasing the altitude and airspeed greatly reduced the operable speed range of the engine by raising the minimum operating speed of the engine. In several runs with the high-flow compressor the maximum engine speed was limited to less than 7600 rpm by combustion blow-out, high tail-pipe temperatures, and compressor stall. Acceleration of the engine was relatively slow and the time required for acceleration increased with altitude. At maximum engine speed a sudden reduction in jet-nozzle area resulted in an immediate increase in thrust. The engine started normally and easily below 20,000 feet with each configuration. The use of a high-voltage ignition system made possible starts at a pressure altitude of 40,000 feet; but on these starts the tail-pipe temperatures were very high, a great deal of fuel burned in and behind the tail-pipe, and acceleration was very slow. Operation of the engine was similar with both fuel regulators except that the modified fuel regulator restricted the fuel flow in such a manner that the acceleration above 6000 rpm was very slow. The bearings did not cool properly at high altitudes and high engine speeds with a low-flow compressor, and bearing cooling was even poorer with a high-flow compressor.

MPCM: a hardware coder for super slow motion video sequences

NASA Astrophysics Data System (ADS)

Alcocer, Estefanía; López-Granado, Otoniel; Gutierrez, Roberto; Malumbres, Manuel P.

2013-12-01

In the last decade, the improvements in VLSI levels and image sensor technologies have led to a frenetic rush to provide image sensors with higher resolutions and faster frame rates. As a result, video devices were designed to capture real-time video at high-resolution formats with frame rates reaching 1,000 fps and beyond. These ultrahigh-speed video cameras are widely used in scientific and industrial applications, such as car crash tests, combustion research, materials research and testing, fluid dynamics, and flow visualization that demand real-time video capturing at extremely high frame rates with high-definition formats. Therefore, data storage capability, communication bandwidth, processing time, and power consumption are critical parameters that should be carefully considered in their design. In this paper, we propose a fast FPGA implementation of a simple codec called modulo-pulse code modulation (MPCM) which is able to reduce the bandwidth requirements up to 1.7 times at the same image quality when compared with PCM coding. This allows current high-speed cameras to capture in a continuous manner through a 40-Gbit Ethernet point-to-point access.

Asymmetric-detection time-stretch optical microscopy (ATOM) for ultrafast high-contrast cellular imaging in flow

PubMed Central

Wong, Terence T. W.; Lau, Andy K. S.; Ho, Kenneth K. Y.; Tang, Matthew Y. H.; Robles, Joseph D. F.; Wei, Xiaoming; Chan, Antony C. S.; Tang, Anson H. L.; Lam, Edmund Y.; Wong, Kenneth K. Y.; Chan, Godfrey C. F.; Shum, Ho Cheung; Tsia, Kevin K.

2014-01-01

Accelerating imaging speed in optical microscopy is often realized at the expense of image contrast, image resolution, and detection sensitivity – a common predicament for advancing high-speed and high-throughput cellular imaging. We here demonstrate a new imaging approach, called asymmetric-detection time-stretch optical microscopy (ATOM), which can deliver ultrafast label-free high-contrast flow imaging with well delineated cellular morphological resolution and in-line optical image amplification to overcome the compromised imaging sensitivity at high speed. We show that ATOM can separately reveal the enhanced phase-gradient and absorption contrast in microfluidic live-cell imaging at a flow speed as high as ~10 m/s, corresponding to an imaging throughput of ~100,000 cells/sec. ATOM could thus be the enabling platform to meet the pressing need for intercalating optical microscopy in cellular assay, e.g. imaging flow cytometry – permitting high-throughput access to the morphological information of the individual cells simultaneously with a multitude of parameters obtained in the standard assay. PMID:24413677

Evaluation of flow quality in two large NASA wind tunnels at transonic speeds

NASA Technical Reports Server (NTRS)

Harvey, W. D.; Stainback, P. C.; Owen, F. K.

1980-01-01

Wind tunnel testing of low drag airfoils and basic transition studies at transonic speeds are designed to provide high quality aerodynamic data at high Reynolds numbers. This requires that the flow quality in facilities used for such research be excellent. To obtain a better understanding of the characteristics of facility disturbances and identification of their sources for possible facility modification, detailed flow quality measurements were made in two prospective NASA wind tunnels. Experimental results are presented of an extensive and systematic flow quality study of the settling chamber, test section, and diffuser in the Langley 8 foot transonic pressure tunnel and the Ames 12 foot pressure wind tunnel. Results indicate that the free stream velocity and pressure fluctuation levels in both facilities are low at subsonic speeds and are so high as to make it difficult to conduct meaningful boundary layer control and transition studies at transonic speeds.

Fast PSP measurements of wall-pressure fluctuation in low-speed flows: improvements using proper orthogonal decomposition

NASA Astrophysics Data System (ADS)

Peng, Di; Wang, Shaofei; Liu, Yingzheng

2016-04-01

Fast pressure-sensitive paint (PSP) is very useful in flow diagnostics due to its fast response and high spatial resolution, but its applications in low-speed flows are usually challenging due to limitations of paint's pressure sensitivity and the capability of high-speed imagers. The poor signal-to-noise ratio in low-speed cases makes it very difficult to extract useful information from the PSP data. In this study, unsteady PSP measurements were made on a flat plate behind a cylinder in a low-speed wind tunnel (flow speed from 10 to 17 m/s). Pressure fluctuations (Δ P) on the plate caused by vortex-plate interaction were recorded continuously by fast PSP (using a high-speed camera) and a microphone array. Power spectrum of pressure fluctuations and phase-averaged Δ P obtained from PSP and microphone were compared, showing good agreement in general. Proper orthogonal decomposition (POD) was used to reduce noise in PSP data and extract the dominant pressure features. The PSP results reconstructed from selected POD modes were then compared to the pressure data obtained simultaneously with microphone sensors. Based on the comparison of both instantaneous Δ P and root-mean-square of Δ P, it was confirmed that POD analysis could effectively remove noise while preserving the instantaneous pressure information with good fidelity, especially for flows with strong periodicity. This technique extends the application range of fast PSP and can be a powerful tool for fundamental fluid mechanics research at low speed.

Gap Winds in a Fjord: Howe Sound, British Columbia.

NASA Astrophysics Data System (ADS)

Jackson, Peter L.

1993-01-01

Gap, outflow, or Squamish wind, is the cold low level seaward flow of air through fjords which dissect the coastal mountain barrier of northwestern North America. These flows, occurring mainly during winter, can be strong, threatening safety, economic activity and comfort. Howe Sound gap winds were studied using a combination of observations and several types of models. Observations of winds in Howe Sound showed that gap wind strength varied considerably along the channel, across the channel and vertically. Generally, winds increase down the channel, are strongest along the eastern side, and are below 1000 m depth. Observations were unable to answer all questions about gap winds due to data sparseness, particularly in the vertical direction. Therefore, several modelling approaches were used. The modelling began with a complete 3-dimensional quasi-Boussinesq model (CSU RAMS) and ended with the creation and testing of models which are conceptually simpler, and more easily interpreted and manipulated. A gap wind simulation made using RAMS was shown to be mostly successful by statistical evaluation compared to other mesoscale simulations, and by visual inspection of the fields. The RAMS output, which has very high temporal and spatial resolution, provided much additional information about the details of gap flow. In particular, RAMS results suggested a close analogy between gap wind and hydraulic channel flow, with hydraulic features such as supercritical flow and hydraulic jumps apparent. These findings imply gap wind flow could potentially be represented by much simpler models. The simplest possible models containing pressure gradient, advection and friction but not incorporating hydraulic effects, were created, tested, and found lacking. A hydraulic model, which in addition incorporates varying gap wind height and channel geometry, was created and shown to successfully simulate gap winds. Force balance analysis from RAMS and the hydraulic model showed that pressure gradient and advection are the most important forces, followed by friction which becomes an important force in fast supercritical flow. The sensitivity of gap wind speed to various parameters was found from sensitivity tests using the hydraulic model. Results indicated that gap wind speed increases with increasing boundary layer height and speed at the head of channel, and increasing synoptic pressure gradient. Gap wind speed decreases with increasing friction, and increasing boundary layer height at the seaward channel end. Increasing temperature differences between the cold gap wind air and the warmer air aloft was found to increase the variability of the flow--higher maximum but lower mean wind speeds.

Effect of Sweep on Cavity Flow Fields at Subsonic and Transonic Speeds

NASA Technical Reports Server (NTRS)

Tracy, Maureen B.; Plentovich, Elizabeth B.; Hemsch, Michael J.; Wilcox, Floyd J.

2012-01-01

An experimental investigation was conducted in the NASA Langley 7 x 10-Foot High Speed Tunnel (HST) to study the effect of leading- and trailing-edge sweep on cavity flow fields for a range of cavity length-to-height (l/h) ratios. The free-stream Mach number was varied from 0.2 to 0.8. The cavity had a depth of 0.5 inches, a width of 2.5 inches, and a maximum length of 12.0 inches. The leading- and trailing-edge sweep was adjusted using block inserts to achieve leading edge sweep angles of 65 deg, 55 deg, 45 deg, 35 deg, and 0 deg. The fore and aft cavity walls were always parallel. The aft wall of the cavity was remotely positioned to achieve a range of length-to-depth ratios. Fluctuating- and static-pressure data were obtained on the floor of the cavity. The fluctuating pressure data were used to determine whether or not resonance occurred in the cavity rather than to provide a characterization of the fluctuating pressure field. Qualitative surface flow visualization was obtained using a technique in which colored water was introduced into the model through static-pressure orifices. A complete tabulation of the mean static-pressure data for the swept leading edge cavities is included.

Modeling visual-based pitch, lift and speed control strategies in hoverflies

PubMed Central

Vercher, Jean-Louis

2018-01-01

To avoid crashing onto the floor, a free falling fly needs to trigger its wingbeats quickly and control the orientation of its thrust accurately and swiftly to stabilize its pitch and hence its speed. Behavioural data have suggested that the vertical optic flow produced by the fall and crossing the visual field plays a key role in this anti-crash response. Free fall behavior analyses have also suggested that flying insect may not rely on graviception to stabilize their flight. Based on these two assumptions, we have developed a model which accounts for hoverflies´ position and pitch orientation recorded in 3D with a fast stereo camera during experimental free falls. Our dynamic model shows that optic flow-based control combined with closed-loop control of the pitch suffice to stabilize the flight properly. In addition, our model sheds a new light on the visual-based feedback control of fly´s pitch, lift and thrust. Since graviceptive cues are possibly not used by flying insects, the use of a vertical reference to control the pitch is discussed, based on the results obtained on a complete dynamic model of a virtual fly falling in a textured corridor. This model would provide a useful tool for understanding more clearly how insects may or not estimate their absolute attitude. PMID:29361632

Analysis of high speed flow, thermal and structural interactions

NASA Technical Reports Server (NTRS)

Thornton, Earl A.

1994-01-01

Research for this grant focused on the following tasks: (1) the prediction of severe, localized aerodynamic heating for complex, high speed flows; (2) finite element adaptive refinement methodology for multi-disciplinary analyses; (3) the prediction of thermoviscoplastic structural response with rate-dependent effects and large deformations; (4) thermoviscoplastic constitutive models for metals; and (5) coolant flow/structural heat transfer analyses.

Computational fluid dynamics research

NASA Technical Reports Server (NTRS)

Chandra, Suresh; Jones, Kenneth; Hassan, Hassan; Mcrae, David Scott

1992-01-01

The focus of research in the computational fluid dynamics (CFD) area is two fold: (1) to develop new approaches for turbulence modeling so that high speed compressible flows can be studied for applications to entry and re-entry flows; and (2) to perform research to improve CFD algorithm accuracy and efficiency for high speed flows. Research activities, faculty and student participation, publications, and financial information are outlined.

Dual-pulse laser ignition of ethylene-air mixtures in a supersonic combustor.

PubMed

Yang, Leichao; An, Bin; Liang, Jianhan; Li, Xipeng; Wang, Zhenguo

2018-04-02

To reduce the energy of an individual laser pulse, dual-pulse laser ignitions (LIs) at various pulse intervals were investigated in a Mach 2.92 scramjet engine fueled with ethylene. For comparison, experiments on a single-pulse LI were also performed. Schlieren visualization and high-speed photography were employed to observe the ignition processes simultaneously. The results indicate that the energy of an individual laser pulse can be reduced by half via a dual-pulse LI method as compared with a single-pulse LI with the same total energy. The reduction of the individual laser pulse energy degrades the requirements on the laser source and the beam delivery system, which facilitates the practical application of LI in hypersonic vehicles. A pulse interval shorter than 40 μs is suggested for dual-pulse LI in the present study. Because of the intense heat loss and radical dissipation in high-speed flows, the pulse interval for dual-pulse LI should be short enough to narrow the spatial distribution of the initial flame kernel.

Large eddy simulations and direct numerical simulations of high speed turbulent reacting flows

NASA Technical Reports Server (NTRS)

Givi, P.; Madnia, C. K.; Steinberger, C. J.; Frankel, S. H.

1992-01-01

The basic objective of this research is to extend the capabilities of Large Eddy Simulations (LES) and Direct Numerical Simulations (DNS) for the computational analyses of high speed reacting flows. In the efforts related to LES, we were primarily involved with assessing the performance of the various modern methods based on the Probability Density Function (PDF) methods for providing closures for treating the subgrid fluctuation correlations of scalar quantities in reacting turbulent flows. In the work on DNS, we concentrated on understanding some of the relevant physics of compressible reacting flows by means of statistical analysis of the data generated by DNS of such flows. In the research conducted in the second year of this program, our efforts focused on the modeling of homogeneous compressible turbulent flows by PDF methods, and on DNS of non-equilibrium reacting high speed mixing layers. Some preliminary work is also in progress on PDF modeling of shear flows, and also on LES of such flows.

Interfacial instability of wormlike micellar solutions sheared in a Taylor-Couette cell

NASA Astrophysics Data System (ADS)

Mohammadigoushki, Hadi; Muller, Susan J.

2014-10-01

We report experiments on wormlike micellar solutions sheared in a custom-made Taylor-Couette (TC) cell. The computer controlled TC cell allows us to rotate both cylinders independently. Wormlike micellar solutions containing water, CTAB, and NaNo3 with different compositions are highly elastic and exhibit shear banding within a range of shear rate. We visualized the flow field in the θ-z as well as r-z planes, using multiple cameras. When subject to low shear rates, the flow is stable and azimuthal, but becomes unstable above a certain threshold shear rate. This shear rate coincides with the onset of shear banding. Visualizing the θ-z plane shows that this instability is characterized by stationary bands equally spaced in the z direction. Increasing the shear rate results to larger wave lengths. Above a critical shear rate, experiments reveal a chaotic behavior reminiscent of elastic turbulence. We also studied the effect of ramp speed on the onset of instability and report an acceleration below which the critical Weissenberg number for onset of instability is unaffected. Moreover, visualizations in the r-z direction reveals that the interface between the two bands undulates. The shear band evolves towards the outer cylinder upon increasing the shear rate, regardless of which cylinder is rotating.

Unsteady Viscous Flow in a High Speed Core Compressor

DTIC Science & Technology

1990-12-01

in a High Speed Core Compressor by M. A. Cherrett DTICJ. D.Bryc ELECTE J. D. Bryce MAR 2 81991 ED Procurement Executive, Ministry of Defence...ESTABLISHMENT Technical Memorandum P 1198 Received for printing 10 December 1990 UNSTEADY VISCOUS FLOW IN A HIGH SPEED CORE COMPRESSOR by M. A. Cherrett J. D...processed in the Compressor," ASME PaperNo 89-GT-24 following manner to determine the periodic (phase-locked Cherrett , MA, 1990, Temperature Error

High Resolution, High-Speed Photography, an Increasingly Prominent Diagnostic in Ballistic Research Experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shaw, L.; Muelder, S.

1999-10-22

High resolution, high-speed photography is becoming a prominent diagnostic in ballistic experimentation. The development of high speed cameras utilizing electro-optics and the use of lasers for illumination now provide the capability to routinely obtain high quality photographic records of ballistic style experiments. The purpose of this presentation is to review in a visual manner the progress of this technology and how it has impacted ballistic experimentation. Within the framework of development at LLNL, we look at the recent history of large format high-speed photography, and present a number of photographic records that represent the state of the art at themore » time they were made. These records are primarily from experiments involving shaped charges. We also present some examples of current photographic technology, developed within the ballistic community, that has application to hydro diagnostic experimentation at large. This paper is designed primarily as an oral-visual presentation. This written portion is to provide general background, a few examples, and a bibliography.« less

Numerical Simulation of High-Speed Turbulent Reacting Flows

NASA Technical Reports Server (NTRS)

Jaberi, F. A.; Colucci, P. J.; James, S.; Givi, P.

1996-01-01

The purpose of this research is to continue our efforts in advancing the state of knowledge in large eddy simulation (LES) methods for computational analysis of high-speed reacting turbulent flows. We have just completed the first year of Phase 3 of this research.

Optical observation of metal jet generated by high speed inclined collision

NASA Astrophysics Data System (ADS)

Mori, A.; Tanaka, S.; Hokamoto, K.

2017-02-01

Explosive welding, one of the high energy rate material processing, is known the technique to weld strongly for the dissimilar metal combinations. When a metal is collided to the other metal at high velocity with a certain angle, good welding is achieved in this technique. Important parameters of the explosive welding method are the collision velocity and the collision angle. And it is necessary to know these parameters to obtain the explosively welded materials of several metals combinations. However, the optical observation for the collision of metal plate accelerated by the explosive is difficult because of the obstruction by the spreading of detonation gas. In the present work a single-stage powder gun and high speed video camera were used to observe the inclined collision of metals at the high velocity. Projectile consisted by a metal disc and sabot was accelerated by the deflagration of a gunpowder and was collided to another metal disc set with a certain angle. Metal jet was generated at the collision point when the projectile was collided to the target disc in the range of suitable conditions. By using this observation system, a series of the flow from the high speed collision to the generation of metal jet could be taken photographs clearly. This investigation shows the experimental results of the similar and dissimilar metal collision, with comparing the visualization of a metal jet simulated numerically.

Tip-leakage cavitation in the clearance of a 2D hydrofoil with fillets: high-speed visualization and PIV/PTV measurements

NASA Astrophysics Data System (ADS)

Zapryagaev, Ivan I.; Timoshevskiy, Mikhail V.; Pervunin, Konstantin S.

2017-09-01

Tip-clearance cavitation is one of the most aggressive forms of cavitation as it can cause surface erosion of hydraulic machinery elements and, as a result, their fatigue damage and disturb designed operating conditions. At present, the literature lacks for detailed experimental data on the inception and development of this type of cavitation at various flow conditions. In the paper, a tip-leakage cavitation occurring in the clearance between an end face of a 2D hydrofoil (a scaled-down model of guide vanes (GV) of a Francis turbine) and a transparent wall of the test section was studied. The experiments were carried out for different cavitating regimes on the cavitation number and two attack angles of 3° and 9°, with the gap size (tip clearance width) varied in the range from 0.4 to 0.8 mm. In order to determine the cavitation inception conditions and investigate the dynamics of the tip-leakage cavitation, a high-speed visualization was applied. A modified PIV/PTV technique with a diverging laser beam instead of a laser light sheet was used to measure the mean velocity distributions within the gap. It was shown that the cavitation pattern on the suction side of the GV model impacts the dynamics of the leakage flow in the gap but does not affect the sheet cavity formed close to the foil leading edge in the clearance as well as its size and dynamics. When the gap size is increased, the tip-leakage cavitation initiates at higher cavitation numbers or, in other words, conditions for the cavitation occurrence become more favorable.

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.

Static and dynamic force/moment measurements in the Eidetics water tunnel

NASA Technical Reports Server (NTRS)

Suarez, Carlos J.; Malcolm, Gerald N.

1994-01-01

Water tunnels have been utilized in one form or another to explore fluid mechanics and aerodynamics phenomena since the days of Leonardo da Vinci. Water tunnel testing is attractive because of the relatively low cost and quick turn-around time to perform flow visualization experiments and evaluate the results. The principal limitation of a water tunnel is that the low flow speed, which provides for detailed visualization, also results in very small hydrodynamic (aerodynamic) forces on the model, which, in the past, have proven to be difficult to measure accurately. However, the advent of semi-conductor strain gage technology and devices associated with data acquisition such as low-noise amplifiers, electronic filters, and digital recording have made accurate measurements of very low strain levels feasible. The principal objective of this research effort was to develop a multi-component strain gage balance to measure forces and moments on models tested in flow visualization water tunnels. A balance was designed that allows measuring normal and side forces, and pitching, yawing and rolling moments (no axial force). The balance mounts internally in the model and is used in a manner typical of wind tunnel balances. The key differences between a water tunnel balance and a wind tunnel balance are the requirement for very high sensitivity since the loads are very low (typical normal force is 0.2 lbs), the need for water proofing the gage elements, and the small size required to fit into typical water tunnel models.

NASA Tech Briefs, September 2003

NASA Technical Reports Server (NTRS)

2003-01-01

Topics include: Oxygen-Partial-Pressure Sensor for Aircraft Oxygen Mask; Three-Dimensional Venturi Sensor for Measuring Extreme Winds; Swarms of Micron-Sized Sensors; Monitoring Volcanoes by Use of Air-Dropped Sensor Packages; Capacitive Sensors for Measuring Masses of Cryogenic Fluids; UHF Microstrip Antenna Array for Synthetic- Aperture Radar; Multimode Broad-Band Patch Antennas; 164-GHz MMIC HEMT Frequency Doubler; GPS Position and Heading Circuitry for Ships; Software for Managing Parametric Studies; Software Aids Visualization of Computed Unsteady Flow; Software for Testing Electroactive Structural Components; Advanced Software for Analysis of High-Speed Rolling-Element Bearings; Web Program for Development of GUIs for Cluster Computers; XML-Based Generator of C++ Code for Integration With GUIs; Oxide Protective Coats for Ir/Re Rocket Combustion Chambers; Simplified Waterproofing of Aerogels; Improved Thermal-Insulation Systems for Low Temperatures; Device for Automated Cutting and Transfer of Plant Shoots; Extension of Liouville Formalism to Postinstability Dynamics; Advances in Thrust-Based Emergency Control of an Airplane; Ultrasonic/Sonic Mechanisms for Drilling and Coring; Exercise Device Would Exert Selectable Constant Resistance; Improved Apparatus for Measuring Distance Between Axles; Six Classes of Diffraction-Based Optoelectronic Instruments; Modernizing Fortran 77 Legacy Codes; Active State Model for Autonomous Systems; Shields for Enhanced Protection Against High-Speed Debris; Scaling of Two-Phase Flows to Partial-Earth Gravity; Neutral-Axis Springs for Thin-Wall Integral Boom Hinges.

Modeling the effect of varying swim speeds on fish passage through velocity barriers

USGS Publications Warehouse

Castro-Santos, T.

2006-01-01

The distance fish can swim through zones of high-velocity flow is an important factor limiting the distribution and conservation of riverine and diadromous fishes. Often, these barriers are characterized by nonuniform flow conditions, and it is likely that fish will swim at varying speeds to traverse them. Existing models used to predict passage success, however, typically include the unrealistic assumption that fish swim at a constant speed regardless of the speed of flow. This paper demonstrates how the maximum distance of ascent through velocity barriers can be estimated from the swim speed-fatigue time relationship, allowing for variation in both swim speed and water velocity.

Pixel-wise deblurring imaging system based on active vision for structural health monitoring at a speed of 100 km/h

NASA Astrophysics Data System (ADS)

Hayakawa, Tomohiko; Moko, Yushi; Morishita, Kenta; Ishikawa, Masatoshi

2018-04-01

In this paper, we propose a pixel-wise deblurring imaging (PDI) system based on active vision for compensation of the blur caused by high-speed one-dimensional motion between a camera and a target. The optical axis is controlled by back-and-forth motion of a galvanometer mirror to compensate the motion. High-spatial-resolution image captured by our system in high-speed motion is useful for efficient and precise visual inspection, such as visually judging abnormal parts of a tunnel surface to prevent accidents; hence, we applied the PDI system for structural health monitoring. By mounting the system onto a vehicle in a tunnel, we confirmed significant improvement in image quality for submillimeter black-and-white stripes and real tunnel-surface cracks at a speed of 100 km/h.

Simulation of High-Speed Droplet Impact Against Dry Substrates with Partial Velocity Slip

NASA Astrophysics Data System (ADS)

Kondo, Tomoki; Ando, Keita

2017-11-01

High-speed droplet impact can be used to clean substrates such as silicon wafers. Radially spreading shear flow after the impact may allow for mechanically removing contaminant particles at substrate surfaces. Since it is a big challenge to experimentally explore such complicated flow that exhibits contact line motion and water hammer, its flow feature is not well understood. Here, we aim to numerically evaluate shear flow caused by the impact of a spherical water droplet (of submillimeter sizes) at high speed (up to 50 m/s) against a dry rigid wall. We model the flow based on compressible Navier-Stokes equations with Stokes' hypothesis and solve them by a high-order-accurate finite volume method equipped with shock and interface capturing. To treat the motion of a contact line between the three phases (the droplet, the rigid wall, and the ambient air) in a robust manner, we permit velocity slip at the wall with Navier's model, for wall slip is known to come into play under steep velocity gradients that can arise from high-speed droplet impact. In our presentation, we will examine radially spreading flow after the droplet impact and the resulting wall shear stress generation from the simulation. This work was supported by JSPS KAKENHI Grant Number JP17J02211.

Why do Cross-Flow Turbines Stall?

NASA Astrophysics Data System (ADS)

Cavagnaro, Robert; Strom, Benjamin; Polagye, Brian

2015-11-01

Hydrokinetic turbines are prone to instability and stall near their peak operating points under torque control. Understanding the physics of turbine stall may help to mitigate this undesirable occurrence and improve the robustness of torque controllers. A laboratory-scale two-bladed cross-flow turbine operating at a chord-based Reynolds number ~ 3 ×104 is shown to stall at a critical tip-speed ratio. Experiments are conducting bringing the turbine to this critical speed in a recirculating current flume by increasing resistive torque and allowing the rotor to rapidly decelerate while monitoring inflow velocity, torque, and drag. The turbine stalls probabilistically with a distribution generated from hundreds of such events. A machine learning algorithm identifies stall events and indicates the effectiveness of available measurements or combinations of measurements as predictors. Bubble flow visualization and PIV are utilized to observe fluid conditions during stall events including the formation, separation, and advection of leading-edge vortices involved in the stall process.

Direct numerical simulation of the laminar-turbulent transition at hypersonic flow speeds on a supercomputer

NASA Astrophysics Data System (ADS)

Egorov, I. V.; Novikov, A. V.; Fedorov, A. V.

2017-08-01

A method for direct numerical simulation of three-dimensional unsteady disturbances leading to a laminar-turbulent transition at hypersonic flow speeds is proposed. The simulation relies on solving the full three-dimensional unsteady Navier-Stokes equations. The computational technique is intended for multiprocessor supercomputers and is based on a fully implicit monotone approximation scheme and the Newton-Raphson method for solving systems of nonlinear difference equations. This approach is used to study the development of three-dimensional unstable disturbances in a flat-plate and compression-corner boundary layers in early laminar-turbulent transition stages at the free-stream Mach number M = 5.37. The three-dimensional disturbance field is visualized in order to reveal and discuss features of the instability development at the linear and nonlinear stages. The distribution of the skin friction coefficient is used to detect laminar and transient flow regimes and determine the onset of the laminar-turbulent transition.

Pulse-burst PIV in a high-speed wind tunnel

NASA Astrophysics Data System (ADS)

Beresh, Steven; Kearney, Sean; Wagner, Justin; Guildenbecher, Daniel; Henfling, John; Spillers, Russell; Pruett, Brian; Jiang, Naibo; Slipchenko, Mikhail; Mance, Jason; Roy, Sukesh

2015-09-01

Time-resolved particle image velocimetry (TR-PIV) has been achieved in a high-speed wind tunnel, providing velocity field movies of compressible turbulence events. The requirements of high-speed flows demand greater energy at faster pulse rates than possible with the TR-PIV systems developed for low-speed flows. This has been realized using a pulse-burst laser to obtain movies at up to 50 kHz, with higher speeds possible at the cost of spatial resolution. The constraints imposed by use of a pulse-burst laser are limited burst duration of 10.2 ms and a low duty cycle for data acquisition. Pulse-burst PIV has been demonstrated in a supersonic jet exhausting into a transonic crossflow and in transonic flow over a rectangular cavity. The velocity field sequences reveal the passage of turbulent structures and can be used to find velocity power spectra at every point in the field, providing spatial distributions of acoustic modes. The present work represents the first use of TR-PIV in a high-speed ground-test facility.

Absorption Filter Based Optical Diagnostics in High Speed Flows

NASA Technical Reports Server (NTRS)

Samimy, Mo; Elliott, Gregory; Arnette, Stephen

1996-01-01

Two major regimes where laser light scattered by molecules or particles in a flow contains significant information about the flow are Mie scattering and Rayleigh scattering. Mie scattering is used to obtain only velocity information, while Rayleigh scattering can be used to measure both the velocity and the thermodynamic properties of the flow. Now, recently introduced (1990, 1991) absorption filter based diagnostic techniques have started a new era in flow visualization, simultaneous velocity and thermodynamic measurements, and planar velocity measurements. Using a filtered planar velocimetry (FPV) technique, we have modified the optically thick iodine filter profile of Miles, et al., and used it in the pressure-broaden regime which accommodates measurements in a wide range of velocity applications. Measuring velocity and thermodynamic properties simultaneously, using absorption filtered based Rayleigh scattering, involves not only the measurement of the Doppler shift, but also the spectral profile of the Rayleigh scattering signal. Using multiple observation angles, simultaneous measurement of one component velocity and thermodynamic properties in a supersonic jet were measured. Presently, the technique is being extended for simultaneous measurements of all three components of velocity and thermodynamic properties.

Embedded function methods for compressible high speed turbulent flow

NASA Technical Reports Server (NTRS)

Walker, J. D. A.

1989-01-01

Fundamental issues relating to compressible turbulent flow are addressed. The focus has been on developing methods and testing concepts for attached flows rather than trying to force a conventional law of the wall into a zone of backflow. Although the dynamics of the near-wall flow in an attached turbulent boundary layer are relatively well documented, the dynamical features of a zone of reversed turbulent flow are not, nor are they well understood. Incompressibility introduces effects and issues that have been dealt with only marginally in the literature, therefore, the present work has been focussed on attached high-speed flows. The wall function method has been extended up through the supersonic to hypersonic speeds. Algorithms have been successfully introduced into the code that calculates the flow all the way to the wall, and testing is being carried out for progressively more complex flow situations.

Aerodynamic Design of a Dual-Flow Mach 7 Hypersonic Inlet System for a Turbine-Based Combined-Cycle Hypersonic Propulsion System

NASA Technical Reports Server (NTRS)

Sanders, Bobby W.; Weir, Lois J.

2008-01-01

A new hypersonic inlet for a turbine-based combined-cycle (TBCC) engine has been designed. This split-flow inlet is designed to provide flow to an over-under propulsion system with turbofan and dual-mode scramjet engines for flight from takeoff to Mach 7. It utilizes a variable-geometry ramp, high-speed cowl lip rotation, and a rotating low-speed cowl that serves as a splitter to divide the flow between the low-speed turbofan and the high-speed scramjet and to isolate the turbofan at high Mach numbers. The low-speed inlet was designed for Mach 4, the maximum mode transition Mach number. Integration of the Mach 4 inlet into the Mach 7 inlet imposed significant constraints on the low-speed inlet design, including a large amount of internal compression. The inlet design was used to develop mechanical designs for two inlet mode transition test models: small-scale (IMX) and large-scale (LIMX) research models. The large-scale model is designed to facilitate multi-phase testing including inlet mode transition and inlet performance assessment, controls development, and integrated systems testing with turbofan and scramjet engines.

The characterisation and application of a pulsed neodymium YAG laser DGV system to a time-varying high-speed flow

NASA Astrophysics Data System (ADS)

Thorpe, S. J.; Quinlan, N.; Ainsworth, R. W.

2000-10-01

Doppler Global Velocimetry (DGV) is a whole-field measurement technique which has attracted significant interest from the fluid-flow research community since its introduction in 1991. Practical implementations of the methodology have focused on two principal laser light sources: the argon ion laser, applied to steady state or slowly varying flows; and the pulsed neodymium YAG laser for the measurement of instantaneous velocity fields. However, the emphasis in the published literature has been very much on research using the argon laser. This paper reports the application of a Q-switched, injection-seeded neodymium YAG laser to the proven Oxford DGV system, and the use of this combination in a short duration unsteady high-speed flow. The pertinent characteristics of the apparatus are described, and the impact of these on the integrity of the resulting velocity measurements is presented. Adaptations to the commercial laser system that make it suitable for application to the measurement of transient high-speed flows are described. Finally, the application of this system to a short duration unsteady flow is described. This application is based on the flow found in a new type of transdermal drug delivery device, where particles of the drug material are projected at high speed through the skin. Whole-field velocities are recorded, and values as high as 800 m/ s are evident.

Impact of left ventricular assist device speed adjustment on exercise tolerance and markers of wall stress.

PubMed

Hayward, Christopher S; Salamonsen, Robert; Keogh, Anne M; Woodard, John; Ayre, Peter; Prichard, Roslyn; Kotlyar, Eugene; Macdonald, Peter S; Jansz, Paul; Spratt, Phillip

2015-09-01

Left ventricular assist devices are crucial in rehabilitation of patients with end-stage heart failure. Whether cardiopulmonary function is enhanced with higher pump output is unknown. 10 patients (aged 39±16 years, mean±SD) underwent monitored adjustment of pump speed to determine minimum safe low speed and maximum safe high speed at rest. Patients were then randomized to these speed settings and underwent three 6-minute walk tests (6MWT) and symptom-limited cardiopulmonary stress tests (CPX) on separate days. Pump speed settings (low, normal and high) resulted in significantly different resting pump flows of 4.43±0.6, 5.03±0.94, and 5.72±1.2 l/min (P<.001). There was a significant enhancement of pump flows (greater at higher speed settings) with exercise (P<0.05). Increased pump speed was associated with a trend to increased 6MWT distance (P=.10); and CPX exercise time (p=.27). Maximum workload achieved and peak oxygen consumption were significantly different comparing low to high pump speed settings only (P<.05). N-terminal-pro-B-type natriuretic peptide release was significantly reduced at higher pump speed with exercise (P<.01). We have found that alteration of pump speed setting resulted in significant variation in estimated pump flow. The high-speed setting was associated with lower natriuretic hormone release consistent with lower myocardial wall stress. This did not, however, improve exercise tolerance.

Evaluation of range and distortion tolerance for high Mach number transonic fan stages. Task 2: Performance of a 1500-foot-per-second tip speed transonic fan stage with variable geometry inlet guide vanes and stator

NASA Technical Reports Server (NTRS)

Bilwakesh, K. R.; Koch, C. C.; Prince, D. C.

1972-01-01

A 0.5 hub/tip radius ratio compressor stage consisting of a 1500 ft/sec tip speed rotor, a variable camber inlet guide vane and a variable stagger stator was designed and tested with undistorted inlet flow, flow with tip radial distortion, and flow with 90 degrees, one-per-rev, circumferential distortion. At the design speed and design IGV and stator setting the design stage pressure ratio was achieved at a weight within 1% of the design flow. Analytical results on rotor tip shock structure, deviation angle and part-span shroud losses at different operating conditions are presented. The variable geometry blading enabled efficient operation with adequate stall margin at the design condition and at 70% speed. Closing the inlet guide vanes to 40 degrees changed the speed-versus-weight flow relationship along the stall line and thus provided the flexibility of operation at off-design conditions. Inlet flow distortion caused considerable losses in peak efficiency, efficiency on a constant throttle line through design pressure ratio at design speed, stall pressure ratio, and stall margin at the 0 degrees IGV setting and high rotative speeds. The use of the 40 degrees inlet guide vane setting enabled partial recovery of the stall margin over the standard constant throttle line.

Stratified charge rotary engine combustion studies

NASA Technical Reports Server (NTRS)

Shock, H.; Hamady, F.; Somerton, C.; Stuecken, T.; Chouinard, E.; Rachal, T.; Kosterman, J.; Lambeth, M.; Olbrich, C.

1989-01-01

Analytical and experimental studies of the combustion process in a stratified charge rotary engine (SCRE) continue to be the subject of active research in recent years. Specifically to meet the demand for more sophisticated products, a detailed understanding of the engine system of interest is warranted. With this in mind the objective of this work is to develop an understanding of the controlling factors that affect the SCRE combustion process so that an efficient power dense rotary engine can be designed. The influence of the induction-exhaust systems and the rotor geometry are believed to have a significant effect on combustion chamber flow characteristics. In this report, emphasis is centered on Laser Doppler Velocimetry (LDV) measurements and on qualitative flow visualizations in the combustion chamber of the motored rotary engine assembly. This will provide a basic understanding of the flow process in the RCE and serve as a data base for verification of numerical simulations. Understanding fuel injection provisions is also important to the successful operation of the stratified charge rotary engine. Toward this end, flow visualizations depicting the development of high speed, high pressure fuel jets are described. Friction is an important consideration in an engine from the standpoint of lost work, durability and reliability. MSU Engine Research Laboratory efforts in accessing the frictional losses associated with the rotary engine are described. This includes work which describes losses in bearing, seal and auxillary components. Finally, a computer controlled mapping system under development is described. This system can be used to map shapes such as combustion chamber, intake manifolds or turbine blades accurately.

Stratified charge rotary engine combustion studies

NASA Astrophysics Data System (ADS)

Shock, H.; Hamady, F.; Somerton, C.; Stuecken, T.; Chouinard, E.; Rachal, T.; Kosterman, J.; Lambeth, M.; Olbrich, C.

1989-07-01

Analytical and experimental studies of the combustion process in a stratified charge rotary engine (SCRE) continue to be the subject of active research in recent years. Specifically to meet the demand for more sophisticated products, a detailed understanding of the engine system of interest is warranted. With this in mind the objective of this work is to develop an understanding of the controlling factors that affect the SCRE combustion process so that an efficient power dense rotary engine can be designed. The influence of the induction-exhaust systems and the rotor geometry are believed to have a significant effect on combustion chamber flow characteristics. In this report, emphasis is centered on Laser Doppler Velocimetry (LDV) measurements and on qualitative flow visualizations in the combustion chamber of the motored rotary engine assembly. This will provide a basic understanding of the flow process in the RCE and serve as a data base for verification of numerical simulations. Understanding fuel injection provisions is also important to the successful operation of the stratified charge rotary engine. Toward this end, flow visualizations depicting the development of high speed, high pressure fuel jets are described. Friction is an important consideration in an engine from the standpoint of lost work, durability and reliability. MSU Engine Research Laboratory efforts in accessing the frictional losses associated with the rotary engine are described. This includes work which describes losses in bearing, seal and auxillary components. Finally, a computer controlled mapping system under development is described. This system can be used to map shapes such as combustion chamber, intake manifolds or turbine blades accurately.

High Speed Vortex Flows

NASA Technical Reports Server (NTRS)

Wood, Richard M.; Wilcox, Floyd J., Jr.; Bauer, Steven X. S.; Allen, Jerry M.

2000-01-01

A review of the research conducted at the National Aeronautics and Space Administration (NASA), Langley Research Center (LaRC) into high-speed vortex flows during the 1970s, 1980s, and 1990s is presented. The data reviewed is for flat plates, cavities, bodies, missiles, wings, and aircraft. These data are presented and discussed relative to the design of future vehicles. Also presented is a brief historical review of the extensive body of high-speed vortex flow research from the 1940s to the present in order to provide perspective of the NASA LaRC's high-speed research results. Data are presented which show the types of vortex structures which occur at supersonic speeds and the impact of these flow structures to vehicle performance and control is discussed. The data presented shows the presence of both small- and large scale vortex structures for a variety of vehicles, from missiles to transports. For cavities, the data show very complex multiple vortex structures exist at all combinations of cavity depth to length ratios and Mach number. The data for missiles show the existence of very strong interference effects between body and/or fin vortices and the downstream fins. It was shown that these vortex flow interference effects could be both positive and negative. Data are shown which highlights the effect that leading-edge sweep, leading-edge bluntness, wing thickness, location of maximum thickness, and camber has on the aerodynamics of and flow over delta wings. The observed flow fields for delta wings (i.e. separation bubble, classical vortex, vortex with shock, etc.) are discussed in the context of' aircraft design. And data have been shown that indicate that aerodynamic performance improvements are available by considering vortex flows as a primary design feature. Finally a discussing of a design approach for wings which utilize vortex flows for improved aerodynamic performance at supersonic speed is presented.

Visualization of hump formation in high-speed gas metal arc welding

NASA Astrophysics Data System (ADS)

Wu, C. S.; Zhong, L. M.; Gao, J. Q.

2009-11-01

The hump bead is a typical weld defect observed in high-speed welding. Its occurrence limits the improvement of welding productivity. Visualization of hump formation during high-speed gas metal arc welding (GMAW) is helpful in the better understanding of the humping phenomena so that effective measures can be taken to suppress or decrease the tendency of hump formation and achieve higher productivity welding. In this study, an experimental system was developed to implement vision-based observation of the weld pool behavior during high-speed GMAW. Considering the weld pool characteristics in high-speed welding, a narrow band-pass and neutral density filter was equipped for the CCD camera, the suitable exposure time was selected and side view orientation of the CCD camera was employed. The events that took place at the rear portion of the weld pools were imaged during the welding processes with and without hump bead formation, respectively. It was found that the variation of the weld pool surface height and the solid-liquid interface at the pool trailing with time shows some useful information to judge whether the humping phenomenon occurs or not.

In-flight flow visualization characteristics of the NASA F-18 high alpha research vehicle at high angles of attack

NASA Technical Reports Server (NTRS)

Fisher, David F.; Delfrate, John H.; Richwine, David M.

1991-01-01

Surface and off-surface flow visualization techniques were used to visualize the 3-D separated flows on the NASA F-18 high alpha research vehicle at high angles of attack. Results near the alpha = 25 to 26 deg and alpha = 45 to 49 deg are presented. Both the forebody and leading edge extension (LEX) vortex cores and breakdown locations were visualized using smoke. Forebody and LEX vortex separation lines on the surface were defined using an emitted fluid technique. A laminar separation bubble was also detected on the nose cone using the emitted fluid technique and was similar to that observed in the wind tunnel test, but not as extensive. Regions of attached, separated, and vortical flow were noted on the wing and the leading edge flap using tufts and flow cones, and compared well with limited wind tunnel results.

Inviscid Limit for Damped and Driven Incompressible Navier-Stokes Equations in mathbb R^2

NASA Astrophysics Data System (ADS)

Ramanah, D.; Raghunath, S.; Mee, D. J.; Rösgen, T.; Jacobs, P. A.

2007-08-01

Experiments to demonstrate the use of the background-oriented schlieren (BOS) technique in hypersonic impulse facilities are reported. BOS uses a simple optical set-up consisting of a structured background pattern, an electronic camera with a high shutter speed and a high intensity light source. The visualization technique is demonstrated in a small reflected shock tunnel with a Mach 4 conical nozzle, nozzle supply pressure of 2.2 MPa and nozzle supply enthalpy of 1.8 MJ/kg. A 20° sharp circular cone and a model of the MUSES-C re-entry body were tested. Images captured were processed using PIV-style image analysis to visualize variations in the density field. The shock angle on the cone measured from the BOS images agreed with theoretical calculations to within 0.5°. Shock standoff distances could be measured from the BOS image for the re-entry body. Preliminary experiments are also reported in higher enthalpy facilities where flow luminosity can interfere with imaging of the background pattern.

The direct, not V1-mediated, functional influence between the thalamus and middle temporal complex in the human brain is modulated by the speed of visual motion.

PubMed

Gaglianese, A; Costagli, M; Ueno, K; Ricciardi, E; Bernardi, G; Pietrini, P; Cheng, K

2015-01-22

The main visual pathway that conveys motion information to the middle temporal complex (hMT+) originates from the primary visual cortex (V1), which, in turn, receives spatial and temporal features of the perceived stimuli from the lateral geniculate nucleus (LGN). In addition, visual motion information reaches hMT+ directly from the thalamus, bypassing the V1, through a direct pathway. We aimed at elucidating whether this direct route between LGN and hMT+ represents a 'fast lane' reserved to high-speed motion, as proposed previously, or it is merely involved in processing motion information irrespective of speeds. We evaluated functional magnetic resonance imaging (fMRI) responses elicited by moving visual stimuli and applied connectivity analyses to investigate the effect of motion speed on the causal influence between LGN and hMT+, independent of V1, using the Conditional Granger Causality (CGC) in the presence of slow and fast visual stimuli. Our results showed that at least part of the visual motion information from LGN reaches hMT+, bypassing V1, in response to both slow and fast motion speeds of the perceived stimuli. We also investigated whether motion speeds have different effects on the connections between LGN and functional subdivisions within hMT+: direct connections between LGN and MT-proper carry mainly slow motion information, while connections between LGN and MST carry mainly fast motion information. The existence of a parallel pathway that connects the LGN directly to hMT+ in response to both slow and fast speeds may explain why MT and MST can still respond in the presence of V1 lesions. Copyright © 2014 IBRO. Published by Elsevier Ltd. All rights reserved.

Initial Piloted Simulation Evaluation of the Reference-H High-Speed Civil Transport Design During Takeoff and Recovery From Limit Flight Conditions

NASA Technical Reports Server (NTRS)

Glaab, Louis J.

1999-01-01

An initial assessment of a proposed High-Speed Civil Transport (HSCT) was conducted in the fall of 1995 at the NASA Langley Research Center. This configuration, known as the Industry Reference-H (Ref.-H), was designed by the Boeing Aircraft Company as part of their work in the High Speed Research program. It included a conventional tail, a cranked-arrow wing, four mixed-flow turbofan engines, and capacity for transporting approximately 300 passengers. The purpose of this assessment was to evaluate and quantify operational aspects of the Reference-H configuration from a pilot's perspective with the additional goal of identifying design strengths as well as any potential configuration deficiencies. This study was aimed at evaluating the Ref.-H configuration at many points of the aircraft's envelope to determine the suitability of the vehicle to accomplish typical mission profiles as well as emergency or envelope-limit conditions. Pilot-provided Cooper-Harper ratings and comments constituted the primary vehicle evaluation metric. The analysis included simulated real-time piloted evaluations, performed in a 6 degree of freedom motion base NASA Langley Visual-Motion Simulator, combined with extensive bath analysis. The assessment was performed using the third major release of the simulation data base (known as Ref.-H cycle 2B).

Toluene laser-induced fluorescence imaging of compressible flows in an expansion tube

NASA Astrophysics Data System (ADS)

Miller, V. A.; Gamba, M.; Mungal, M. G.; Hanson, R. K.; Mohri, K.; Schulz, C.

2011-11-01

Laser-induced fluorescence (LIF) imaging using toluene as a tracer molecule has been developed for high-speed, low-to-moderate enthalpy conditions in the Stanford 6-inch Expansion Tube. The approach is demonstrated on three canonical compressible flow configurations: (i) supersonic flow over a 20° wedge, (ii) around a cylinder, and (iii) a supersonic boundary layer. Under constant-pressure conditions, toluene LIF offers unique sensitivity to temperature and can therefore be used as an accurate thermometry diagnostic for supersonic flows; on the other hand, for variable-pressure flow fields (e.g., flow around a blunt body), toluene LIF imaging is demonstrated to be an effective flow visualization tool. The three configurations selected demonstrate the diagnostic in these two capacities. For all configurations considered in the study, toluene (0.6% by volume) is seeded into a nitrogen freestream at a Mach number ~ 2.2, T ~ 500K, and p ~ 1.5 bar. A frequency-quadrupled pulsed Nd:YAG laser is used to excite the tracer, and the resulting fluorescence is captured by an ICCD camera. Synthetic fluorescence signals from CFD solutions of each case have been computed and compare favorably to measured signals. Sponsored by DoE PSAAP at Stanford University.

Andreas Acrivos Dissertation Award: Onset of Dynamic Wetting Failure - The Mechanics of High-Speed Fluid Displacement

NASA Astrophysics Data System (ADS)

Vandre, Eric

2014-11-01

Dynamic wetting is crucial to processes where a liquid displaces another fluid along a solid surface, such as the deposition of a coating liquid onto a moving substrate. Dynamic wetting fails when process speed exceeds some critical value, leading to incomplete fluid displacement and transient phenomena that impact a variety of applications, such as microfluidic devices, oil-recovery systems, and splashing droplets. Liquid coating processes are particularly sensitive to wetting failure, which can induce air entrainment and other catastrophic coating defects. Despite the industrial incentives for careful control of wetting behavior, the hydrodynamic factors that influence the transition to wetting failure remain poorly understood from empirical and theoretical perspectives. This work investigates the fundamentals of wetting failure in a variety of systems that are relevant to industrial coating flows. A hydrodynamic model is developed where an advancing fluid displaces a receding fluid along a smooth, moving substrate. Numerical solutions predict the onset of wetting failure at a critical substrate speed, which coincides with a turning point in the steady-state solution path for a given set of system parameters. Flow-field analysis reveals a physical mechanism where wetting failure results when capillary forces can no longer support the pressure gradients necessary to steadily displace the receding fluid. Novel experimental systems are used to measure the substrate speeds and meniscus shapes associated with the onset of air entrainment during wetting failure. Using high-speed visualization techniques, air entrainment is identified by the elongation of triangular air films with system-dependent size. Air films become unstable to thickness perturbations and ultimately rupture, leading to the entrainment of air bubbles. Meniscus confinement in a narrow gap between the substrate and a stationary plate is shown to delay air entrainment to higher speeds for a variety of water/glycerol solutions. In addition, liquid pressurization (relative to ambient air) further postpones air entrainment when the meniscus is located near a sharp corner along the plate. Recorded critical speeds compare well to predictions from the model, supporting the hydrodynamic mechanism for the onset of wetting failure. Lastly, the industrial practice of curtain coating is investigated using the hydrodynamic model. Due to the complexity of this system, a new computational approach is developed combining a finite element method and lubrication theory in order to improve the efficiency of the numerical analysis. Results show that the onset of wetting failure varies strongly with the operating conditions of this system. In addition, stresses from the air flow dramatically affect the steady wetting behavior of curtain coating. Ultimately, these findings emphasize the important role of two-fluid displacement mechanics in high-speed wetting systems.

Visualizing Oil Process Dynamics in Porous Media with Micromodels

NASA Astrophysics Data System (ADS)

Biswal, S. L.

2016-12-01

The use of foam in enhanced oil recovery (EOR) applications is being considered for gas mobility control to ensure pore-trapped oil can be effectively displaced. In fractured reservoirs, gas tends to channel only through the highly permeability regions, bypassing the less permeable porous matrix, where most of the residual oil remains. Because of the unique transport problems presented by the large permeability contrast between fractures and adjacent porous media, we aim to understand the mechanism by which foam transitions from the fracture to the matrix and how initially trapped oil can be displaced and ultimately recovered. My lab has generated micromodels, which are combined with high-speed imaging to visualize foam transport in models with permeability contrasts, fractures, and multiple phases. The wettability of these surfaces can be altered to mimic the heterogeneous wettability found in reservoir systems. We have shown how foam quality can be modulated by adjusting the ratio of gas flow ratio to aqueous flow rate in a flow focusing system and this foam quality influences sweep efficiency in heterogeneous porous media systems. I will discuss how this understanding has allowed us to design better foam EOR processes. I will also highlight our recent efforts in ashaltene deposition. Asphaltene deposition is a common cause of significant flow assurance problems in wellbores and production equipment as well as near-wellbore regions in oil reservoirs. I will present our results for visualizing real time asphaltene deposition from model and crude oils using microfluidic devices. In particular, we consider porous-media micromodel designs to represent various flow conditions typical of that found in oil flow processes. Also, four stages of deposition have been found and investigated in the pore scale and with qualitatively macroscopic total collector efficiency as well as Hamaker expressions for interacting asphaltenes with surfaces. By understanding the nature and the mechanisms of asphaltene deposits, we increase our ability to design cost effective mitigation strategies that includes the development of a new generation of asphaltene deposition inhibitors and improved methods for prevention and treatment of this problem.

A study of sea lion hydrodynamics using a robotic foreflipper platform

NASA Astrophysics Data System (ADS)

Kulkarni, Aditya A.; Patel, Rahi K.; Leftwich, Megan C.

2016-11-01

Unlike most fish and mammals-that utilize BCF swimming-sea lions rely on their foreflippers to generate thrust without a characteristic flapping frequency. This unique swimming style allows the sea lion to be highly maneuverable, while also producing high amounts of thrust. To explore this motion, and the physics that underlies it, we use novel markerless tracking techniques on untrained sea lions at the Smithsonian National Zoo in Washington, D.C to get the complete motion during different maneuvers. High speed video and three-dimensional surface reconstruction techniques are used to extract the foreflippers kinematics during the thrust phase. Using this data, pitch angle is calculated with respect to the base of the flipper to build a scaled robotic flipper. Dye visualization is carried out in a water channel by injecting dye upstream of the leading edge of the flipper with flow speed set to explore different parameters, like Reynolds number or angular velocity. Results show low pressure on the upper surface of the flipper causes the fluid to be pulled around the flipper forming a vortex that moves fully out of the plane.

In situ flash x-ray high-speed computed tomography for the quantitative analysis of highly dynamic processes

NASA Astrophysics Data System (ADS)

Moser, Stefan; Nau, Siegfried; Salk, Manfred; Thoma, Klaus

2014-02-01

The in situ investigation of dynamic events, ranging from car crash to ballistics, often is key to the understanding of dynamic material behavior. In many cases the important processes and interactions happen on the scale of milli- to microseconds at speeds of 1000 m s-1 or more. Often, 3D information is necessary to fully capture and analyze all relevant effects. High-speed 3D-visualization techniques are thus required for the in situ analysis. 3D-capable optical high-speed methods often are impaired by luminous effects and dust, while flash x-ray based methods usually deliver only 2D data. In this paper, a novel 3D-capable flash x-ray based method, in situ flash x-ray high-speed computed tomography is presented. The method is capable of producing 3D reconstructions of high-speed processes based on an undersampled dataset consisting of only a few (typically 3 to 6) x-ray projections. The major challenges are identified, discussed and the chosen solution outlined. The application is illustrated with an exemplary application of a 1000 m s-1 high-speed impact event on the scale of microseconds. A quantitative analysis of the in situ measurement of the material fragments with a 3D reconstruction with 1 mm voxel size is presented and the results are discussed. The results show that the HSCT method allows gaining valuable visual and quantitative mechanical information for the understanding and interpretation of high-speed events.

NASA Lewis 9- by 15-foot low-speed wind tunnel user manual

NASA Technical Reports Server (NTRS)

Soeder, Ronald H.

1993-01-01

This manual describes the 9- by 15-Foot Low-Speed Wind Tunnel at the Lewis Research Center and provides information for users who wish to conduct experiments in this atmospheric facility. Tunnel variables such as pressures, temperatures, available tests section area, and Mach number ranges (0.05 to 0.20) are discussed. In addition, general support systems such as air systems, hydraulic system, hydrogen system, laser system, flow visualization system, and model support systems are described. Instrumentation and data processing and acquisition systems are also discussed.

Head-bobbing behavior in foraging Whooping Cranes

USGS Publications Warehouse

Cronin, T.; Kinloch, M.; Olsen, Glenn H.

2006-01-01

Many species of cursorial birds 'head-bob', that is, they alternately thrust the head forward, then hold it stiII as they walk. Such a motion stabilizes visual fields intermittently and could be critical for visual search; yet the time available for stabilization vs. forward thrust varies with walking speed. Whooping Cranes (Grus americana) are extremely tall birds that visually search the ground for seeds, berries, and small prey. We examined head movements in unrestrained Whooping Cranes using digital video subsequently analyzed with a computer graphical overlay. When foraging, the cranes walk at speeds that allow the head to be held still for at least 50% of the time. This behavior is thought to balance the two needs for covering as much ground as possible and for maximizing the time for visual fixation of the ground in the search for prey. Our results strongly suggest that in cranes, and probably many other bird species, visual fixation of the ground is required for object detection and identification. The thrust phase of the head-bobbing cycle is probably also important for vision. As the head moves forward, the movement generates visual flow and motion parallax, providing visual cues for distances and the relative locations of objects. The eyes commonly change their point of fixation when the head is moving too, suggesting that they remain visually competent throughout the entire cycle of thrust and stabilization.

High-Speed Schlieren Movies of the Flow About Reefed Parachute Models Towed at Supersonic Speeds Behind a Conical Body (4.875 Inches in Diameter). Drag Values Based on the Unreefed Diameter of 1.73 F. Porosity of Unreefed Parachute is 28 Percent.

NASA Technical Reports Server (NTRS)

1960-01-01

Flexible parachute models reefed to one-eighth, one-fourth, one-third, and four tenths of its diameter were towed at speeds of Mach 1.80, 2.00, 2.20 and 2.87. Towline lengths tested were 23.40, 24.38, 26.81, and 29.25 inches. High-speed Schlieren movies of the flow are shown.

Effects of Various Fillet Shapes on a 76/40 Double Delta Wing from Mach 0.18 to 0.7

NASA Technical Reports Server (NTRS)

Erickson, Gary E.; Bell, James H.; Gonzalez, Hugo A.; McLachlan, Blair G.

2003-01-01

The effects of linear, diamond, and parabolic fillets on a double delta wing were investigated in the NASA Langley 7 x 10 ft High Speed Tunnel from Mach 0.18 to 0.7 and angles of attack from 4 deg. to 42 deg. Force and moment, pneumatic pressures, pressure sensitive paint, and vapor screen flow visualization measurements were used to characterize the flow field and to determine longitudinal forces and moments. The fillets increased lift coefficient and reduced induced drag without significantly affecting pitching moment. Pressure sensitive paint showed the increase in lift is caused by an increase in suction and broadening of the vortex suction footprint. Vapor screen results showed the mixing and coalescing of the strake fillet and wing vortices causes the footprint to broaden.

Subsonic flow investigations on a cranked wing designed for high maneuverability

NASA Technical Reports Server (NTRS)

Rao, D. M.

1986-01-01

The characteristic pitching moment nonlinearity of cranked wings limits their usable lift coefficient well below C sub L max. The potential of several aerodynamic devices, viz., fences, pylon vortex generators (PVG), mid-span strakes and cavity flaps, in delaying the pitch up onset on a 70/50 deg cranked wing was explored in low speed tunnel tests. Upper surface pressure measurements and low visualizations were conducted on a semi-span wing model to observe the vortex flow development with increasing angle of attack, and then to assess the effectiveness of the devices in controlling the collapse of vortex lift over the wing panel outboard of the crank. Force tests on a full span wing and body model were also conducted to assess the fence and PVG in improving the usable C sub L.

Label-free and highly sensitive optical imaging of detailed microcirculation within meninges and cortex in mice with the cranium left intact.

PubMed

Jia, Yali; An, Lin; Wang, Ruikang K

2010-01-01

We demonstrate for the first time that the detailed blood flow distribution within intracranial dura mater and cortex can be visualized by an ultrahigh sensitive optical microangiography (UHS-OMAG). The study uses an UHS-OMAG system operating at 1310 nm with an imaging speed at 150 frames per second that requires approximately 10 s to complete one 3-D scan of approximately 2.5 x 2.5 mm(2). The system is sensitive to blood flow with a velocity ranging from approximately 4 microms to approximately 23 mms. We show superior performance of UHS-OMAG in providing functional images of capillary level microcirculation within meninges in mice with the cranium left intact, the results of which correlate well with the standard dural histopathology.

Label-free and highly sensitive optical imaging of detailed microcirculation within meninges and cortex in mice with the cranium left intact

PubMed Central

Jia, Yali; An, Lin; Wang, Ruikang K.

2010-01-01

We demonstrate for the first time that the detailed blood flow distribution within intracranial dura mater and cortex can be visualized by an ultrahigh sensitive optical microangiography (UHS-OMAG). The study uses an UHS-OMAG system operating at 1310 nm with an imaging speed at 150 frames per second that requires ∼10 s to complete one 3-D scan of ∼2.5×2.5 mm2. The system is sensitive to blood flow with a velocity ranging from ∼4 μm∕s to ∼23 mm∕s. We show superior performance of UHS-OMAG in providing functional images of capillary level microcirculation within meninges in mice with the cranium left intact, the results of which correlate well with the standard dural histopathology. PMID:20614993

The development of an experimental facility and investigation of rapidly maneuvering Micro-Air-Vehicle wings

NASA Astrophysics Data System (ADS)

Wilson, Lee Alexander

Vertical Takeoff-and-Landing (VTOL) Micro Air Vehicles (MAVs) provide a versatile operational platform which combines the capabilities of fixed wing and rotary wing MAVs. In order to improve performance of these vehicles, a better understanding of the rapid transition between horizontal and vertical flight is required. This study examines the flow structures around the Mini-Vertigo VTOL MAV using flow visualization techniques. This will gives an understanding of the flow structures which dominate the flight dynamics of rapid pitching maneuvers. This study consists of three objectives: develop an experimental facility, use flow visualization to investigate the flow around the experimental subject during pitching, and analyze the results. The flow around the Mini-Vertigo VTOL MAV is dominated by the slipstream from its propellers. The slipstream delays LE separation and causes drastic deflection in the flow. While the frequency of the vortices shed from the LE and TE varies with flow speed, the non-dimensional frequency does not. It does, however, vary slightly with the pitching rate. These results are applicable across a wide range of flight conditions. The results correlate to previous research done to examine the aerodynamic forces on the MAV.

How Lovebirds Maneuver Rapidly Using Super-Fast Head Saccades and Image Feature Stabilization

PubMed Central

Kress, Daniel; van Bokhorst, Evelien; Lentink, David

2015-01-01

Diurnal flying animals such as birds depend primarily on vision to coordinate their flight path during goal-directed flight tasks. To extract the spatial structure of the surrounding environment, birds are thought to use retinal image motion (optical flow) that is primarily induced by motion of their head. It is unclear what gaze behaviors birds perform to support visuomotor control during rapid maneuvering flight in which they continuously switch between flight modes. To analyze this, we measured the gaze behavior of rapidly turning lovebirds in a goal-directed task: take-off and fly away from a perch, turn on a dime, and fly back and land on the same perch. High-speed flight recordings revealed that rapidly turning lovebirds perform a remarkable stereotypical gaze behavior with peak saccadic head turns up to 2700 degrees per second, as fast as insects, enabled by fast neck muscles. In between saccades, gaze orientation is held constant. By comparing saccade and wingbeat phase, we find that these super-fast saccades are coordinated with the downstroke when the lateral visual field is occluded by the wings. Lovebirds thus maximize visual perception by overlying behaviors that impair vision, which helps coordinate maneuvers. Before the turn, lovebirds keep a high contrast edge in their visual midline. Similarly, before landing, the lovebirds stabilize the center of the perch in their visual midline. The perch on which the birds land swings, like a branch in the wind, and we find that retinal size of the perch is the most parsimonious visual cue to initiate landing. Our observations show that rapidly maneuvering birds use precisely timed stereotypic gaze behaviors consisting of rapid head turns and frontal feature stabilization, which facilitates optical flow based flight control. Similar gaze behaviors have been reported for visually navigating humans. This finding can inspire more effective vision-based autopilots for drones. PMID:26107413

Note: High-speed Z tip scanner with screw cantilever holding mechanism for atomic-resolution atomic force microscopy in liquid

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reza Akrami, Seyed Mohammad; Miyata, Kazuki; Asakawa, Hitoshi

High-speed atomic force microscopy has attracted much attention due to its unique capability of visualizing nanoscale dynamic processes at a solid/liquid interface. However, its usability and resolution have yet to be improved. As one of the solutions for this issue, here we present a design of a high-speed Z-tip scanner with screw holding mechanism. We perform detailed comparison between designs with different actuator size and screw arrangement by finite element analysis. Based on the design giving the best performance, we have developed a Z tip scanner and measured its performance. The measured frequency response of the scanner shows a flatmore » response up to ∼10 kHz. This high frequency response allows us to achieve wideband tip-sample distance regulation. We demonstrate the applicability of the scanner to high-speed atomic-resolution imaging by visualizing atomic-scale calcite crystal dissolution process in water at 2 s/frame.« less

Performance of large-bore tapered-roller bearings under combined radial and thrust load at shaft speeds to 15,000 rpm

NASA Technical Reports Server (NTRS)

Parker, R. J.; Signer, H. R.

1977-01-01

The performance of 120.65-mm bore tapered roller bearings was investigated at shaft speeds up to 15,000 rpm. Temperature distribution and bearing heat generation were determined as a function of shaft speed, radial and thrust loads, lubricant flow rate, and lubricant inlet temperature. Lubricant was supplied by either jets or by a combination of holes through the cone directly to the cone-rib contact and jets at the roller small-end side. Cone-rib lubrication significantly improved high-speed tapered-roller bearing performance, yielding lower cone-face temperatures and lower power loss and allowing lower lubricant flow rates for a given speed condition. Bearing temperatures increased with increased shaft speed and decreased with increased lubricant flow rate. Bearing power loss increased with increased shaft speed and increased lubricant flow rate.

Photoacoustic thermal flowmetry with a single light source

NASA Astrophysics Data System (ADS)

Liu, Wei; Lan, Bangxin; Hu, Leo; Chen, Ruimin; Zhou, Qifa; Yao, Junjie

2017-09-01

We report a photoacoustic thermal flowmetry based on optical-resolution photoacoustic microscopy (OR-PAM) using a single laser source for both thermal tagging and photoacoustic excitation. When an optically absorbing medium is flowing across the optical focal zone of OR-PAM, a small volume of the medium within the optical focus is repeatedly illuminated and heated by a train of laser pulses with a high repetition rate. The average temperature of the heated volume at each laser pulse is indicated by the photoacoustic signal excited by the same laser pulse due to the well-established linear relationship between the Grueneisen coefficient and the local temperature. The thermal dynamics of the heated medium volume, which are closely related to the flow speed, can therefore be measured from the time course of the detected photoacoustic signals. Here, we have developed a lumped mathematical model to describe the time course of the photoacoustic signals as a function of the medium's flow speed. We conclude that the rising time constant of the photoacoustic signals is linearly dependent on the flow speed. Thus, the flow speed can be quantified by fitting the measured photoacoustic signals using the derived mathematical model. We first performed proof-of-concept experiments using defibrinated bovine blood flowing in a plastic tube. The experiment results have demonstrated that the proposed method has high accuracy (˜±6%) and a wide range of measurable flow speeds. We further validated the method by measuring the blood flow speeds of the microvasculature in a mouse ear in vivo.

A bio-inspired flying robot sheds light on insect piloting abilities.

PubMed

Franceschini, Nicolas; Ruffier, Franck; Serres, Julien

2007-02-20

When insects are flying forward, the image of the ground sweeps backward across their ventral viewfield and forms an "optic flow," which depends on both the groundspeed and the groundheight. To explain how these animals manage to avoid the ground by using this visual motion cue, we suggest that insect navigation hinges on a visual-feedback loop we have called the optic-flow regulator, which controls the vertical lift. To test this idea, we built a micro-helicopter equipped with an optic-flow regulator and a bio-inspired optic-flow sensor. This fly-by-sight micro-robot can perform exacting tasks such as take-off, level flight, and landing. Our control scheme accounts for many hitherto unexplained findings published during the last 70 years on insects' visually guided performances; for example, it accounts for the fact that honeybees descend in a headwind, land with a constant slope, and drown when travelling over mirror-smooth water. Our control scheme explains how insects manage to fly safely without any of the instruments used onboard aircraft to measure the groundheight, groundspeed, and descent speed. An optic-flow regulator is quite simple in terms of its neural implementation and just as appropriate for insects as it would be for aircraft.

Ultrascale collaborative visualization using a display-rich global cyberinfrastructure.

PubMed

Jeong, Byungil; Leigh, Jason; Johnson, Andrew; Renambot, Luc; Brown, Maxine; Jagodic, Ratko; Nam, Sungwon; Hur, Hyejung

2010-01-01

The scalable adaptive graphics environment (SAGE) is high-performance graphics middleware for ultrascale collaborative visualization using a display-rich global cyberinfrastructure. Dozens of sites worldwide use this cyberinfrastructure middleware, which connects high-performance-computing resources over high-speed networks to distributed ultraresolution displays.

Flame-Vortex Interactions in Microgravity to Improve Models of Turbulent Combustion

NASA Technical Reports Server (NTRS)

Driscoll, James F.

1999-01-01

A unique flame-vortex interaction experiment is being operated in microgravity in order to obtain fundamental data to assess the Theory of Flame Stretch which will be used to improve models of turbulent combustion. The experiment provides visual images of the physical process by which an individual eddy in a turbulent flow increases the flame surface area, changes the local flame propagation speed, and can extinguish the reaction. The high quality microgravity images provide benchmark data that are free from buoyancy effects. Results are used to assess Direct Numerical Simulations of Dr. K. Kailasanath at NRL, which were run for the same conditions.

Vision and air flow combine to streamline flying honeybees

PubMed Central

Taylor, Gavin J.; Luu, Tien; Ball, David; Srinivasan, Mandyam V.

2013-01-01

Insects face the challenge of integrating multi-sensory information to control their flight. Here we study a ‘streamlining' response in honeybees, whereby honeybees raise their abdomen to reduce drag. We find that this response, which was recently reported to be mediated by optic flow, is also strongly modulated by the presence of air flow simulating a head wind. The Johnston's organs in the antennae were found to play a role in the measurement of the air speed that is used to control the streamlining response. The response to a combination of visual motion and wind is complex and can be explained by a model that incorporates a non-linear combination of the two stimuli. The use of visual and mechanosensory cues increases the strength of the streamlining response when the stimuli are present concurrently. We propose this multisensory integration will make the response more robust to transient disturbances in either modality. PMID:24019053

The effects of leading edge modifications on the post-stall characteristics of wings

NASA Technical Reports Server (NTRS)

Winkelmann, A. E.; Barlow, J. B.; Saini, J. K.; Anderson, J. D., Jr.; Jones, E.

1980-01-01

An investigation of the effects of leading edge modifications on the post-stall characteristics of two rectangular planform wings in a series of low speed wind tunnel tests is presented. Abrupt discontinuities in the leading edge shape of the wings were produced by placing a nose glove over a portion of the span or by deflecting sections of a segmented leading edge flap. Six component balance data, oil flow visualization photographs, and pressure distribution measurements were obtained, and tests made to study the development of flow separation at stall on small scale planform wing models. Results of oil flow visualization tests at and beyond stall showed the formation of counter-rotating swirl patterns on the upper surface of the '2-D' and '3-D' wings, and results of a numerical lifting line technique applied to wings with leading edge modifications are included.

Experimental Investigation of a Helicopter Rotor Hub Flow

NASA Astrophysics Data System (ADS)

Reich, David

The rotor hub system is by far the largest contributor to helicopter parasite drag and a barrier to increasing helicopter forward-flight speed and range. Additionally, the hub sheds undesirable vibration- and instability-inducing unsteady flow over the empennage. The challenges associated with rotor hub flows are discussed, including bluff body drag, interactional aerodynamics, and the effect of the turbulent hub wake on the helicopter empennage. This study was conducted in three phases to quantify model-scale rotor hub flows in water tunnels at The Pennsylvania State University Applied research lab. The first phase investigated scaling and component interaction effects on a 1:17 scale rotor hub model in the 12-inch diameter water tunnel. Effects of Reynolds number, advance ratio, and hub geometry configuration on the drag and wake shed from the rotor hub were quantified using load cell measurements and particle-image velocimetry (PIV). The second phase focused on flow visualization and measurement on a rotor hub and rotor hub/pylon geometry in the 12-inch diameter water tunnel. Stereo PIV was conducted in a cross plane downstream of the hub and flow visualization was conducted using oil paint and fluorescent dye. The third phase concentrated on high accuracy load measurement and prediction up to full-scale Reynolds number on a 1:4.25 scale model in the 48-inch diameter water tunnel. Measurements include 6 degree of freedom loads on the hub and two-component laser-Doppler velocimetry in the wake. Finally, results and conclusions are discussed, followed by recommendations for future investigations.

Numerical Simulation of High-Speed Turbulent Reacting Flows

NASA Technical Reports Server (NTRS)

Givi, P.; Taulbee, D. B.; Madnia, C. K.; Jaberi, F. A.; Colucci, P. J.; Gicquel, L. Y. M.; Adumitroaie, V.; James, S.

1999-01-01

The objectives of this research are: (1) to develop and implement a new methodology for large eddy simulation of (LES) of high-speed reacting turbulent flows. (2) To develop algebraic turbulence closures for statistical description of chemically reacting turbulent flows. We have just completed the third year of Phase III of this research. This is the Final Report of our activities on this research sponsored by the NASA LaRC.

Numerical investigation of flow on NACA4412 aerofoil with different aspect ratios

NASA Astrophysics Data System (ADS)

Demir, Hacımurat; Özden, Mustafa; Genç, Mustafa Serdar; Çağdaş, Mücahit

2016-03-01

In this study, the flow over NACA4412 was investigated both numerically and experimentally at a different Reynolds numbers. The experiments were carried out in a low speed wind tunnel with various angles of attack and different Reynolds numbers (25000 and 50000). Airfoil was manufactured using 3D printer with a various aspect ratios (AR = 1 and AR = 3). Smoke-wire and oil flow visualization methods were used to visualize the surface flow patterns. NACA4412 aerofoil was designed by using SOLIDWORKS. The structural grid of numerical model was constructed by ANSYS ICEM CFD meshing software. Furthermore, ANSYS FLUENT™ software was used to perform numerical calculations. The numerical results were compared with experimental results. Bubble formation was shown in CFD streamlines and smoke-wire experiments at z / c = 0.4. Furthermore, bubble shrunk at z / c = 0.2 by reason of the effects of tip vortices in both numerical and experimental studies. Consequently, it was seen that there was a good agreement between numerical and experimental results.

Laboratory Facilities and Measurement Techniques for Beamed-Energy-Propulsion Experiments in Brazil

NASA Astrophysics Data System (ADS)

de Oliveira, Antonio Carlos; Chanes Júnior, José Brosler; Cordeiro Marcos, Thiago Victor; Pinto, David Romanelli; Santos Vilela, Renan Guilherme; Barros Galvão, Victor Alves; Mantovani, Arthur Freire; da Costa, Felipe Jean; dos Santos Assenção, José Adeildo; dos Santos, Alberto Monteiro; de Paula Toro, Paulo Gilberto; Sala Minucci, Marco Antonio; da Silveira Rêgo, Israel; Salvador, Israel Irone; Myrabo, Leik N.

2011-11-01

Laser propulsion is an innovative concept of accessing the space easier and cheaper where the propulsive energy is beamed to the aerospace vehicle in flight from ground—or even satellite-based high-power laser sources. In order to be realistic about laser propulsion, the Institute for Advanced Studies of the Brazilian Air Force in cooperation with the United States Air Force and the Rensselaer Polytechnic Institute are seriously investigating its basic physics mechanisms and engineering aspects at the Henry T. Hamamatsu Laboratory of Hypersonic and Aerothermodynamics in São José dos Campos, Brazil. This paper describes in details the existing facilities and measuring systems such as high-power laser devices, pulsed-hypersonic wind tunnels and high-speed flow visualization system currently utilized in the laboratory for experimentation on laser propulsion.

Effect of Thickness-to-Chord Ratio on Flow Structure of Low Swept Delta Wing

NASA Astrophysics Data System (ADS)

Gulsacan, Burak; Sencan, Gizem; Yavuz, Mehmet Metin

2017-11-01

The effect of thickness-to-chord (t/C) ratio on flow structure of a delta wing with sweep angle of 35 degree is characterized in a low speed wind tunnel using laser illuminated smoke visualization, particle image velocimetry, and surface pressure measurements. Four different t/C ratio varying from 4.75% to 19% are tested at angles of attack 4, 6, 8, and 10 degrees for Reynolds numbers Re =10,000 and 35,000. The results indicate that the effect of thickness-to-chord ratio on flow structure is quite substantial, such that, as the wing thickness increases, the flow structure transforms from leading edge vortex to three-dimensional separated flow regime. The wing with low t/C ratio of 4.75% experiences pronounced surface separation at significantly higher angle of attack compared to the wing with high t/C ratio. The results might explain some of the discrepancies reported in previously conducted studies related to delta wings. In addition, it is observed that the thickness of the shear layer separated from windward side of the wing is directly correlated with the thickness of the wing. To conclude, the flow structure on low swept delta wing is highly affected by t/C ratio, which in turn might indicate the potential usage of wing thickness as an effective flow control parameter.

An Assessment of Gigabit Ethernet Technology and Its Applications at the NASA Glenn Research Center

NASA Technical Reports Server (NTRS)

Bakes, Catherine Murphy; Kim, Chan M.; Ramos, Calvin T.

2000-01-01

This paper describes Gigabit Ethernet and its role in supporting R&D programs at NASA Glenn. These programs require an advanced high-speed network capable of transporting multimedia traffic, including real-time visualization, high- resolution graphics, and scientific data. GigE is a 1 Gbps extension to 10 and 100 Mbps Ethernet. The IEEE 802.3z and 802.3ab standards define the MAC layer and 1000BASE-X and 1000BASE-T physical layer specifications for GigE. GigE switches and buffered distributors support IEEE 802.3x flow control. The paper also compares GigE with ATM in terms of quality of service, data rate, throughput, scalability, interoperability, network management, and cost of ownership.

Investigation of Flow Separation in a Transonic-fan Linear Cascade Using Visualization Methods

NASA Technical Reports Server (NTRS)

Lepicovsky, Jan; Chima, Rodrick V.; Jett, Thomas A.; Bencic, Timothy J.; Weiland, Kenneth E.

2000-01-01

An extensive study into the nature of the separated flows on the suction side of modem transonic fan airfoils at high incidence is described in the paper. Suction surface.flow separation is an important flow characteristic that may significantly contribute to stall flutter in transonic fans. Flutter in axial turbomachines is a highly undesirable and dangerous self-excited mode of blade oscillations that can result in high cycle fatigue blade failure. The study basically focused on two visualization techniques: surface flow visualization using dye oils, and schlieren (and shadowgraph) flow visualization. The following key observations were made during the study. For subsonic inlet flow, the flow on the suction side of the blade is separated over a large portion of the blade, and the separated area increases with increasing inlet Mach number. For the supersonic inlet flow condition, the flow is attached from the leading edge up to the point where a bow shock from the upper neighboring blade hits the blade surface. Low cascade solidity, for the subsonic inlet flow, results in an increased area of separated flow. For supersonic flow conditions, a low solidity results in an improvement in flow over the suction surface. Finally, computational results modeling the transonic cascade flowfield illustrate our ability to simulate these flows numerically.

Visualization of cavitating and flashing flows within a high aspect ratio injector

NASA Astrophysics Data System (ADS)

Thompson, Andrew S.

Thermal management issues necessitate the use of fuel as a heat sink for gas turbine and liquid rocket engines. There are certain benefits to using heated fuels, namely, increased sensible enthalpy, increased combustion efficiency, a decrease in certain emissions, and enhanced vaporization characteristics. However, the thermal and pressure enviornment inside an injector can result in the fuel flashing to vapor. Depending on the injector design, this can have deleterious effects on engine performance. As interest in heated fuels inreases, it is important to understand what occurs in the flow path of an injector under flashing conditions. At the High Pressure Laboratory at Purdue University's Maurice J. Zucrow Laboritories, a test rig was designed and built to give visual access into the flow path of a 2-D slot injector. The rig is capable of pressurizing and heating a liquid to superheated conditions and utilizes a pneumatically actuated piston to pusth the liquid through the slot injector. Methanol was chosen as a surrogate fuel to allow for high levels of superheat at relatively low temperatures. Testing was completed with acrylic and quartz injectors of varying L/DH. Flashing conditions inside the injector flow path were induced via a combination of heating and back pressure adjustments. Volume flow rate, pressure measurements, and temperature measurements were made which allowed the discharge characteristics, the level of superheat, and other parameters to be calculated and compared. To give a basis for comparison the flashing results are compared to the flow through the injector under cavitating conditions. Cavitation and flashing appear to be related phenomena and this relationship is shown. Bubble formation under cavitating or flashing conditions is observed to attenuate the injector's discharge characteristics. High speed videos of the flow field were also collected. Several flow regimes and flow structures, unique to these regimes, were observed. A frequency analysis was also performed on the video files. Bubble formation in the flow field dominates the frequency spectrum, which is confined below 1 kHz. The test campaign was successful. The result is a possible way to predict an injector's performance under flashing conditions without running heated fuel through the injector. These results may be applicable to real world injector design and testing.

Visual motion transforms visual space representations similarly throughout the human visual hierarchy.

PubMed

Harvey, Ben M; Dumoulin, Serge O

2016-02-15

Several studies demonstrate that visual stimulus motion affects neural receptive fields and fMRI response amplitudes. Here we unite results of these two approaches and extend them by examining the effects of visual motion on neural position preferences throughout the hierarchy of human visual field maps. We measured population receptive field (pRF) properties using high-field fMRI (7T), characterizing position preferences simultaneously over large regions of the visual cortex. We measured pRFs properties using sine wave gratings in stationary apertures, moving at various speeds in either the direction of pRF measurement or the orthogonal direction. We find direction- and speed-dependent changes in pRF preferred position and size in all visual field maps examined, including V1, V3A, and the MT+ map TO1. These effects on pRF properties increase up the hierarchy of visual field maps. However, both within and between visual field maps the extent of pRF changes was approximately proportional to pRF size. This suggests that visual motion transforms the representation of visual space similarly throughout the visual hierarchy. Visual motion can also produce an illusory displacement of perceived stimulus position. We demonstrate perceptual displacements using the same stimulus configuration. In contrast to effects on pRF properties, perceptual displacements show only weak effects of motion speed, with far larger speed-independent effects. We describe a model where low-level mechanisms could underlie the observed effects on neural position preferences. We conclude that visual motion induces similar transformations of visuo-spatial representations throughout the visual hierarchy, which may arise through low-level mechanisms. Copyright © 2015 Elsevier Inc. All rights reserved.

Shock waves in aviation security and safety

NASA Astrophysics Data System (ADS)

Settles, G. S.; Keane, B. T.; Anderson, B. W.; Gatto, J. A.

Accident investigations such as of Pan Am 103 and TWA 800 reveal the key role of shock-wave propagation in destroying the aircraft when an on-board explosion occurs. This paper surveys shock wave propagation inside an aircraft fuselage, caused either by a terrorist device or by accident, and provides some new experimental results. While aircraft-hardening research has been under way for more than a decade, no such experiments to date have used the crucial tool of high-speed optical imaging to visualize shock motion. Here, Penn State's Full-Scale Schlieren flow visualization facility yields the first shock-motion images in aviation security scenarios: 1) Explosions beneath full-size aircraft seats occupied by mannequins, 2) Explosions inside partially-filled luggage containers, and 3) Luggage-container explosions resulting in hull-holing. Both single-frame images and drum-camera movies are obtained. The implications of these results are discussed, though the overall topic must still be considered in its infancy.

Parallel Computation and Visualization of Three-dimensional, Time-dependent, Thermal Convective Flows

NASA Technical Reports Server (NTRS)

Wang, P.; Li, P.

1998-01-01

A high-resolution numerical study on parallel systems is reported on three-dimensional, time-dependent, thermal convective flows. A parallel implentation on the finite volume method with a multigrid scheme is discussed, and a parallel visualization systemm is developed on distributed systems for visualizing the flow.

Calibration, Information, and Control Strategies for Braking to Avoid a Collision

ERIC Educational Resources Information Center

Fajen, Brett R.

2005-01-01

This study explored visual control strategies for braking to avoid collision by manipulating information about speed of self-motion. Participants watched computer-generated displays and used a brake to stop at an object in the path of motion. Global optic flow rate and edge rate were manipulated by adjusting eyeheight and ground-texture size.…

Reaction time and anticipatory skill of athletes in open and closed skill-dominated sport.

PubMed

Nuri, Leila; Shadmehr, Azadeh; Ghotbi, Nastaran; Attarbashi Moghadam, Behrouz

2013-01-01

In sports, reaction time and anticipatory skill are critical aspects of perceptual abilities. To date, no study has compared reaction time and anticipatory skill of athletes from open and closed skill-dominated sport. Accordingly, the present study investigated whether a difference exists in sensory-cognitive skills between these two different sport domains. Eleven volleyball players and 11 sprinters participated in this experiment. Reaction time and anticipatory skill of both groups were recorded by a custom-made software called SART (speed anticipation and reaction time test). This software consists of six sensory-cognitive tests that evaluate visual choice reaction time, visual complex choice reaction time, auditory choice reaction time, auditory complex choice reaction time, and anticipatory skill of the high speed and low speed of the ball. For each variable, an independent t-test was performed. Results suggested that sprinters were better in both auditory reaction times (P<0.001 for both tests) and volleyball players were better in both anticipatory skill tests (P = 0.007 and P = 0.04 for anticipatory skill of the high speed and low speed of the ball, respectively). However, no significant differences were found in both visual choice reaction time tests (P > 0.05 for both visual reaction time tests). It is concluded that athletes have greater sensory-cognitive skills related to their specific sport domain either open or closed.

Hot gas ingestion characteristics and flow visualization of a vectored thrust STOVL concept

NASA Technical Reports Server (NTRS)

Johns, Albert L.; Neiner, George H.; Bencic, Timothy J.; Flood, Joseph D.; Amuedo, Kurt C.; Strock, Thomas W.; Williams, Ben R.

1990-01-01

A 9.2 percent scale short takeoff and vertical landing (STOVL) hot gas ingestion model was designed and built by McDonnell Douglas Corporation (MCAIR) and tested in the NASA Lewis Research Center 9- by 15-Foot Low Speed Wind Tunnel (LSWT). Hot gas ingestion, the entrainment of heated engine exhaust into the inlet flow field, is a key development issue for advanced short takeoff and vertical landing aircraft. The Phase 1 test program, conducted by NASA Lewis and McDonnell Douglas Corporation, evaluated the hot ingestion phenomena and control techniques and Phase 2 test program which was conducted by NASA Lewis are both reported. The Phase 2 program was conducted at exhaust nozzles temperatures up to 1460 R and utilized a sheet laser system for flow visualization of the model flow field in and out of ground effects. Hot gas ingestion levels were measured for the several forward nozzle splay configurations and with flow control/lift improvement devices which reduced the hot gas ingestion. The model support system had four degrees of freedom, heated high pressure air for nozzle flow, and a suction system exhaust for inlet flow. The headwind (freestream) velocity for Phase 1 was varied from 8 to 90 kn, with primary data taken in the 8 to 23 kn headwind velocity range. Phase 2 headwind velocity varied from 10 to 23 kn. Results of both Phase 1 and 2 are presented. A description of the model, facility, a new model support system, and a sheet laser illumination system are also provided. Results are presented over a range of main landing gear height (model height) above the ground plane at a 10 kn headwind velocity. The results contain the compressor face pressure and temperature distortions, total pressure recovery, compressor face temperature rise, and the environmental effects of the hot gas. The environmental effects include the ground plane temperature and pressure distributions, model airframe heating, and the location of the ground flow separation. Results from the sheet laser flow visualization test are also shown.

Process optimization of an auger pyrolyzer with heat carrier using response surface methodology.

PubMed

Brown, J N; Brown, R C

2012-01-01

A 1 kg/h auger reactor utilizing mechanical mixing of steel shot heat carrier was used to pyrolyze red oak wood biomass. Response surface methodology was employed using a circumscribed central composite design of experiments to optimize the system. Factors investigated were: heat carrier inlet temperature and mass flow rate, rotational speed of screws in the reactor, and volumetric flow rate of sweep gas. Conditions for maximum bio-oil and minimum char yields were high flow rate of sweep gas (3.5 standard L/min), high heat carrier temperature (∼600 °C), high auger speeds (63 RPM) and high heat carrier mass flow rates (18 kg/h). Regression models for bio-oil and char yields are described including identification of a novel interaction effect between heat carrier mass flow rate and auger speed. Results suggest that auger reactors, which are rarely described in literature, are well suited for bio-oil production. The reactor achieved liquid yields greater than 73 wt.%. Copyright © 2011 Elsevier Ltd. All rights reserved.

Forecasting the short-term passenger flow on high-speed railway with neural networks.

PubMed

Xie, Mei-Quan; Li, Xia-Miao; Zhou, Wen-Liang; Fu, Yan-Bing

2014-01-01

Short-term passenger flow forecasting is an important component of transportation systems. The forecasting result can be applied to support transportation system operation and management such as operation planning and revenue management. In this paper, a divide-and-conquer method based on neural network and origin-destination (OD) matrix estimation is developed to forecast the short-term passenger flow in high-speed railway system. There are three steps in the forecasting method. Firstly, the numbers of passengers who arrive at each station or depart from each station are obtained from historical passenger flow data, which are OD matrices in this paper. Secondly, short-term passenger flow forecasting of the numbers of passengers who arrive at each station or depart from each station based on neural network is realized. At last, the OD matrices in short-term time are obtained with an OD matrix estimation method. The experimental results indicate that the proposed divide-and-conquer method performs well in forecasting the short-term passenger flow on high-speed railway.

Large Eddy Simulations (LES) and Direct Numerical Simulations (DNS) for the computational analyses of high speed reacting flows

NASA Technical Reports Server (NTRS)

Givi, Peyman; Madnia, Cyrus K.; Steinberger, C. J.; Frankel, S. H.

1992-01-01

The principal objective is to extend the boundaries within which large eddy simulations (LES) and direct numerical simulations (DNS) can be applied in computational analyses of high speed reacting flows. A summary of work accomplished during the last six months is presented.

High-Speed Magnetohydrodynamic Flow Control Analyses With 3-D Simulations

DTIC Science & Technology

2008-01-01

color. 14. ABSTRACT Magnetohydrodynamic studies of high-speed flow control are described with emphasis on understanding fluid response to specific...interactions play a crucial role by distorting the velocity field. The interaction with an external circuit through electrodes is relatively efficient when... Entropy layer . . . . . . . . . . . . . 20 6 Energy management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 7 Conclusion

Blade tip, finite aspect ratio, and dynamic stall effects on the Darrieus rotor

NASA Astrophysics Data System (ADS)

Paraschivoiu, I.; Desy, P.; Masson, C.

1988-02-01

The objective of the work described in this paper was to apply the Boeing-Vertol dynamic stall model in an asymmetric manner to account for the asymmetry of the flow between the left and right sides of the rotor. This phenomenon has been observed by the flow visualization of a two-straight-bladed Darrieus rotor in the IMST water tunnel. Also introduced into the aerodynamic model are the effects of the blade tip and finite aspect ratio on the aerodynamic performance of the Darrieus wind turbine. These improvements are compatible with the double-multiple-streamtube model and have been included in the CARDAAV computer code for predicting the aerodynamic performance. Very good agreement has been observed between the test data (Sandia 17 m) and theoretical predictions; a significant improvement over the previous dynamic stall model was obtained for the rotor power at low tip speed ratios, while the inclusion of the finite aspect ratio effects enhances the prediction of the rotor power for high tip speed ratios. The tip losses and finite aspect ratio effects were also calculated for a small-scale vertical-axis wind turbine, with a two-straight-bladed (NACA 0015) rotor.

Numerical simulation of hydrodynamic processes beneath a wind-driven water surface

NASA Astrophysics Data System (ADS)

Tsai, Wu-ting

Turbulent flow driven by a constant wind stress acting at the water surface was simulated numerically to gain a better understanding of the hydrodynamic processes governing the transfer of slightly soluble gases across the atmosphere-water interfaces. Simulation results show that two distinct flow features, attributed to subsurface surface renewal eddies, appear at the water surface. The first characteristic feature is surface streaming, which consists of high-speed streaks aligned with the wind stress. Floating Lagrangian particles, which are distributed uniformly at the water surface, merge to the predominantly high-speed streaks and form elongated streets immediately after they are released. The second characteristic surface signatures are localized low-speed spots which emerge randomly at the water surface. A high-speed streak bifurcates and forms a dividing flow when it encounters a low-speed surface spot. These coherent surface flow structures are qualitatively identical to those observed in the experiment of Melville et al. [1998]. The persistence of these surface features also suggests that there must exist organized subsurface vortical structures that undergo autonomous generation cycles maintained by self-sustaining mechanisms. These coherent vortical flows serve as the renewal eddies that pump the submerged fluids toward the water surface and bring down the upper fluids, and therefore enhance the scalar exchange between the atmosphere and the water body.

[Design and optimization of wireless power and data transmission for visual prosthesis].

PubMed

Lei, Xuping; Wu, Kaijie; Zhao, Lei; Chai, Xinyu

2013-11-01

Boosting spatial resolution of visual prostheses is an effective method to improve implant subjects' visual perception. However, power consumption of visual implants greatly rises with the increasing number of implanted electrodes. In respond to this trend, visual prostheses need to develop high-efficiency wireless power transmission and high-speed data transmission. This paper presents a review of current research progress on wireless power and data transmission for visual prostheses, analyzes relative principles and requirement, and introduces design methods of power and data transmission.

Experimental Study on Ice Forming Process of Cryogenic Liquid Releasing underwater

NASA Astrophysics Data System (ADS)

Zhang, Bin; Wu, Wanqing; Zhang, Xingdong; Zhang, Yi; Zhang, Chuanlin; Zhang, Haoran; Wang, Peng

2017-11-01

Cryogenic liquid releasing into water would be a process combines hyperactive boiling with ice forming. There are still few researches on the experimental study on the environmental conditions for deciding ice forming speed and liquid surviving state. In this paper, to advance our understanding of ice forming deciding factors in the process of LN2 releasing underwater, a visualization experimental system is built. The results show that the pressure difference significantly influences the ice forming speed and liquid surviving distance, which is observed by the experiment and theoretically analysed by Kelvin-Helmholtz instability. Adding nucleating agent is helpful to provide ice nucleus which can accelerate the ice forming speed. Water flowing has some effect on changing pressure difference, which can affect the ice forming speed and liquid surviving distance.

Embodied linearity of speed control in Drosophila melanogaster.

PubMed

Medici, V; Fry, S N

2012-12-07

Fruitflies regulate flight speed by adjusting their body angle. To understand how low-level posture control serves an overall linear visual speed control strategy, we visually induced free-flight acceleration responses in a wind tunnel and measured the body kinematics using high-speed videography. Subsequently, we reverse engineered the transfer function mapping body pitch angle onto flight speed. A linear model is able to reproduce the behavioural data with good accuracy. Our results show that linearity in speed control is realized already at the level of body posture-mediated speed control and is therefore embodied at the level of the complex aerodynamic mechanisms of body and wings. Together with previous results, this study reveals the existence of a linear hierarchical control strategy, which can provide relevant control principles for biomimetic implementations, such as autonomous flying micro air vehicles.

Embodied linearity of speed control in Drosophila melanogaster

PubMed Central

Medici, V.; Fry, S. N.

2012-01-01

Fruitflies regulate flight speed by adjusting their body angle. To understand how low-level posture control serves an overall linear visual speed control strategy, we visually induced free-flight acceleration responses in a wind tunnel and measured the body kinematics using high-speed videography. Subsequently, we reverse engineered the transfer function mapping body pitch angle onto flight speed. A linear model is able to reproduce the behavioural data with good accuracy. Our results show that linearity in speed control is realized already at the level of body posture-mediated speed control and is therefore embodied at the level of the complex aerodynamic mechanisms of body and wings. Together with previous results, this study reveals the existence of a linear hierarchical control strategy, which can provide relevant control principles for biomimetic implementations, such as autonomous flying micro air vehicles. PMID:22933185

3D-PTV around Operational Wind Turbines

NASA Astrophysics Data System (ADS)

Brownstein, Ian; Dabiri, John

2016-11-01

Laboratory studies and numerical simulations of wind turbines are typically constrained in how they can inform operational turbine behavior. Laboratory experiments are usually unable to match both pertinent parameters of full-scale wind turbines, the Reynolds number (Re) and tip speed ratio, using scaled-down models. Additionally, numerical simulations of the flow around wind turbines are constrained by the large domain size and high Re that need to be simulated. When these simulations are preformed, turbine geometry is typically simplified resulting in flow structures near the rotor not being well resolved. In order to bypass these limitations, a quantitative flow visualization method was developed to take in situ measurements of the flow around wind turbines at the Field Laboratory for Optimized Wind Energy (FLOWE) in Lancaster, CA. The apparatus constructed was able to seed an approximately 9m x 9m x 5m volume in the wake of the turbine using artificial snow. Quantitative measurements were obtained by tracking the evolution of the artificial snow using a four camera setup. The methodology for calibrating and collecting data, as well as preliminary results detailing the flow around a 2kW vertical-axis wind turbine (VAWT), will be presented.

Visual adaptation alters the apparent speed of real-world actions.

PubMed

Mather, George; Sharman, Rebecca J; Parsons, Todd

2017-07-27

The apparent physical speed of an object in the field of view remains constant despite variations in retinal velocity due to viewing conditions (velocity constancy). For example, people and cars appear to move across the field of view at the same objective speed regardless of distance. In this study a series of experiments investigated the visual processes underpinning judgements of objective speed using an adaptation paradigm and video recordings of natural human locomotion. Viewing a video played in slow-motion for 30 seconds caused participants to perceive subsequently viewed clips played at standard speed as too fast, so playback had to be slowed down in order for it to appear natural; conversely after viewing fast-forward videos for 30 seconds, playback had to be speeded up in order to appear natural. The perceived speed of locomotion shifted towards the speed depicted in the adapting video ('re-normalisation'). Results were qualitatively different from those obtained in previously reported studies of retinal velocity adaptation. Adapting videos that were scrambled to remove recognizable human figures or coherent motion caused significant, though smaller shifts in apparent locomotion speed, indicating that both low-level and high-level visual properties of the adapting stimulus contributed to the changes in apparent speed.

Measurement of surface shear stress vector beneath high-speed jet flow using liquid crystal coating

NASA Astrophysics Data System (ADS)

Wang, Cheng-Peng; Zhao, Ji-Song; Jiao, Yun; Cheng, Ke-Ming

2018-05-01

The shear-sensitive liquid crystal coating (SSLCC) technique is investigated in the high-speed jet flow of a micro-wind-tunnel. An approach to measure surface shear stress vector distribution using the SSLCC technique is established, where six synchronous cameras are used to record the coating color at different circumferential view angles. Spatial wall shear stress vector distributions on the test surface are obtained at different velocities. The results are encouraging and demonstrate the great potential of the SSLCC technique in high-speed wind-tunnel measurement.

Comparison of gamma densitometry and electrical capacitance measurements applied to hold-up prediction of oil–water flow patterns in horizontal and slightly inclined pipes

NASA Astrophysics Data System (ADS)

Perera, Kshanthi; Kumara, W. A. S.; Hansen, Fredrik; Mylvaganam, Saba; Time, Rune W.

2018-06-01

Measurement techniques are vital for the control and operation of multiphase oil–water flow in pipes. The development of such techniques depends on laboratory experiments involving flow visualization, liquid fraction (‘hold-up’), phase slip and pressure drop measurements. They provide valuable information by revealing the physics, spatial and temporal structures of complex multiphase flow phenomena. This paper presents the hold-up measurement of oil–water flow in pipelines using gamma densitometry and electrical capacitance tomography (ECT) sensors. The experiments were carried out with different pipe inclinations from  ‑5° to  +6° for selected mixture velocities (0.2–1.5 m s‑1), and at selected watercuts (0.05–0.95). Mineral oil (Exxsol D60) and water were used as test fluids. Nine flow patterns were identified including a new pattern called stratified wavy and mixed interface flow. As a third direct method, visual observations and high-speed videos were used for the flow regime and interface identification. ECT and gamma densitometry hold-up measurements show similar trends for changes in pipeline inclinations. Changing the pipe inclination affected the flow mostly at lower mixture velocities and caused a change of flow patterns, allowing the highest change of hold-up. ECT hold-up measurements overpredict the gamma densitometry measurements at higher input water cuts and underpredict at intermediate water cuts. Gamma hold-up results showed good agreement with the literature results, having a maximum deviation of 6%, while it was as high as 22% for ECT in comparison to gamma densitometry. Uncertainty analysis of the measurement techniques was carried out with single-phase oil flow. This shows that the measurement error associated with gamma densitometry is approximately 3.2%, which includes 1.3% statistical error and 2.9% error identified as electromagnetically induced noise in electronics. Thus, gamma densitometry can predict hold-up with a higher accuracy in comparison to ECT when applied to oil–water systems at minimized electromagnetic noise.

Large Scale Behavior and Droplet Size Distributions in Crude Oil Jets and Plumes

NASA Astrophysics Data System (ADS)

Katz, Joseph; Murphy, David; Morra, David

2013-11-01

The 2010 Deepwater Horizon blowout introduced several million barrels of crude oil into the Gulf of Mexico. Injected initially as a turbulent jet containing crude oil and gas, the spill caused formation of a subsurface plume stretching for tens of miles. The behavior of such buoyant multiphase plumes depends on several factors, such as the oil droplet and bubble size distributions, current speed, and ambient stratification. While large droplets quickly rise to the surface, fine ones together with entrained seawater form intrusion layers. Many elements of the physics of droplet formation by an immiscible turbulent jet and their resulting size distribution have not been elucidated, but are known to be significantly influenced by the addition of dispersants, which vary the Weber Number by orders of magnitude. We present experimental high speed visualizations of turbulent jets of sweet petroleum crude oil (MC 252) premixed with Corexit 9500A dispersant at various dispersant to oil ratios. Observations were conducted in a 0.9 m × 0.9 m × 2.5 m towing tank, where large-scale behavior of the jet, both stationary and towed at various speeds to simulate cross-flow, have been recorded at high speed. Preliminary data on oil droplet size and spatial distributions were also measured using a videoscope and pulsed light sheet. Sponsored by Gulf of Mexico Research Initiative (GoMRI).

Dynamics of flexible molecules in thinning fluid filaments

NASA Astrophysics Data System (ADS)

Arratia, Paulo E.; Juarez, Gabriel

2011-11-01

Newtonian liquids that contain small amounts (~ppm) of flexible polymers can exhibit viscoelastic behavior in extensional flows. In this talk, we report the results of experiments on the thinning and breakup of polymeric fluids in a simple microfluidic device. We aim to understand the stretching dynamics of flexible polymers by direct visualization of fluorescent DNA molecules, a model polymer. A Boger fluid, composed of 100 ppm polyacrylamide and 85% w/w glycerol, is seeded with stained lambdaâDNA molecules (<10% v/v) imaged by high speed epifluorescence microscopy. We observe that the strong flow in the thinning fluid threads provide sufficient forces to stretch the DNA molecules away from their equilibrium coiled state. The distribution of stretch lengths, however, is very heterogeneous due to molecular individualism and initial conditions. Once the molecules are stretched to their full length and aligned with the flow, they translate along the fluid thread as rigid rods until the point of pinch off. After pinch off, both the fluid and molecules return to a relaxed state.

On the nonlinear aerodynamic and stability characteristics of a generic chine-forebody slender-wing fighter configuration

NASA Technical Reports Server (NTRS)

Erickson, Gary E.; Brandon, Jay M.

1987-01-01

An exploratory investigation was conducted of the nonlinear aerodynamic and stability characteristics of a tailless generic fighter configuration featuring a chine-shaped forebody coupled to a slender cropped delta wing in the NASA Langley Research Center's 12-Foot Low-Speed Wind Tunnel. Forebody and wing vortex flow mechanisms were identified through off-body flow visualizations to explain the trends in the longitudinal and lateral-directional characteristics at extreme attitudes (angles of attack and sideslip). The interactions of the vortical motions with centerline and wing-mounted vertical tail surfaces were studied and the flow phenomena were correlated with the configuration forces and moments. Single degree of freedom, free-to-roll tests were used to study the wing rock susceptibility of the generic fighter model. Modifications to the nose region of the chine forebody were examined and fluid mechanisms were established to account for their ineffectiveness in modulating the highly interactive forebody and wing vortex systems.

Dynamic PIV measurement of a compressible flow issuing from an airbag inflator nozzle

NASA Astrophysics Data System (ADS)

Lee, Sang Joon; Jang, Young Gil; Kim, Seok; Kim, Chang Soo

2006-12-01

Among many equipment for passenger safety, the air bag system is the most fundamental and effective device for an automobile. The inflator housing is a main part of the curtain-type air bag system, which supplies high-pressure gases in pumping up the air bag-curtain which is increasingly being adapted in deluxe cars for protecting passengers from the danger of side clash. However, flow information on the inflator housing is very limited. In this study, we measure the instantaneous velocity fields of a high-speed compressible flow issuing from the exit nozzle of an inflator housing using a dynamic PIV system. From the velocity field data measured at a high frame-rate, we evaluate the variation of the mass flow rate with time. The dynamic PIV system consists of a high-repetition Nd:YLF laser, a high-speed CMOS camera, and a delay generator. The flow images are taken at 4000 fps with synchronization of the trigger signal for inflator ignition. From the instantaneous velocity field data of flow ejecting from the airbag inflator housing at the initial stage, we can see a flow pattern of broken shock wave front and its downward propagation. The flow ejecting from the inflator housing is found to have very high velocity fluctuations, with the maximum velocity at about 700 m/s. The time duration of the high-speed flow is very short, and there is no perceptible flow after 100 ms.

Investigation of the cavitating flow in injector nozzles for diesel and biodiesel

NASA Astrophysics Data System (ADS)

Zhong, Wenjun; He, Zhixia; Wang, Qian; Jiang, Zhaochen; Fu, Yanan

2013-07-01

In diesel engines, the cavitating flow in nozzles greatly affects the fuel atomization characteristics and then the subsequent combustion and exhaust emissions. At present the biodiesel is a kind of prospective alternative fuel in diesel engines, the flow characteristics for the biodiesel fuel need to be investigated. In this paper, based on the third-generation synchrotrons of Shanghai Synchrotron Radiation facility (SSRF), a high-precision three-dimension structure of testing nozzle with detailed internal geometry information was obtained using X-ray radiography for a more accurate physical model. A flow visualization experiment system with a transparent scaled-up vertical multi-hole injector nozzle tip was setup. A high resolution and speed CCD camera equipped with a long distance microscope device was used to acquire flow images of diesel and biodiesel fuel, respectively. Then, the characteristics of cavitating flow and their effects on the fuel atomization characteristics were investigated. The experimental results show that the nozzle cavitating flow of both the diesel and biodiesel fuel could be divided into four regimes: turbulent flow, cavitation inception, development of cavitation and hydraulic flip. The critical pressures of both the cavitating flow and hydraulic flip of biodiesel are higher than those of diesel. The spray cone angle increases as the cavitation occurs, but it decreases when the hydraulic flip appears. Finally, it can be concluded that the Reynolds number decreases with the increase of cavitation number, and the discharge coefficient increases with the increase of cavitation number.

Evaluation of the Wind Flow Variability Using Scanning Doppler Lidar Measurements

NASA Astrophysics Data System (ADS)

Sand, S. C.; Pichugina, Y. L.; Brewer, A.

2016-12-01

Better understanding of the wind flow variability at the heights of the modern turbines is essential to accurately assess of generated wind power and efficient turbine operations. Nowadays the wind energy industry often utilizes scanning Doppler lidar to measure wind-speed profiles at high spatial and temporal resolution.The study presents wind flow features captured by scanning Doppler lidars during the second Wind Forecast and Improvement Project (WFIP 2) sponsored by the Department of Energy (DOE) and National Oceanic and Atmospheric Administration (NOAA). This 18-month long experiment in the Columbia River Basin aims to improve model wind forecasts complicated by mountain terrain, coastal effects, and numerous wind farms.To provide a comprehensive dataset to use for characterizing and predicting meteorological phenomena important to Wind Energy, NOAA deployed scanning, pulsed Doppler lidars to two sites in Oregon, one at Wasco, located upstream of all wind farms relative to the predominant westerly flow in the region, and one at Arlington, located in the middle of several wind farms.In this presentation we will describe lidar scanning patterns capable of providing data in conical, or vertical-slice modes. These individual scans were processed to obtain 15-min averaged profiles of wind speed and direction in real time. Visualization of these profiles as time-height cross sections allows us to analyze variability of these parameters with height, time and location, and reveal periods of rapid changes (ramp events). Examples of wind flow variability between two sites of lidar measurements along with examples of reduced wind velocity downwind of operating turbines (wakes) will be presented.

Usage of CO2 microbubbles as flow-tracing contrast media in X-ray dynamic imaging of blood flows.

PubMed

Lee, Sang Joon; Park, Han Wook; Jung, Sung Yong

2014-09-01

X-ray imaging techniques have been employed to visualize various biofluid flow phenomena in a non-destructive manner. X-ray particle image velocimetry (PIV) was developed to measure velocity fields of blood flows to obtain hemodynamic information. A time-resolved X-ray PIV technique that is capable of measuring the velocity fields of blood flows under real physiological conditions was recently developed. However, technical limitations still remained in the measurement of blood flows with high image contrast and sufficient biocapability. In this study, CO2 microbubbles as flow-tracing contrast media for X-ray PIV measurements of biofluid flows was developed. Human serum albumin and CO2 gas were mechanically agitated to fabricate CO2 microbubbles. The optimal fabricating conditions of CO2 microbubbles were found by comparing the size and amount of microbubbles fabricated under various operating conditions. The average size and quantity of CO2 microbubbles were measured by using a synchrotron X-ray imaging technique with a high spatial resolution. The quantity and size of the fabricated microbubbles decrease with increasing speed and operation time of the mechanical agitation. The feasibility of CO2 microbubbles as a flow-tracing contrast media was checked for a 40% hematocrit blood flow. Particle images of the blood flow were consecutively captured by the time-resolved X-ray PIV system to obtain velocity field information of the flow. The experimental results were compared with a theoretically amassed velocity profile. Results show that the CO2 microbubbles can be used as effective flow-tracing contrast media in X-ray PIV experiments.

Subsonic investigations of vortex interaction control for enhanced high-alpha aerodynamics of a chine forebody/Delta wing configuration

NASA Technical Reports Server (NTRS)

Rao, Dhanvada M.; Bhat, M. K.

1992-01-01

A proposed concept to alleviate high alpha asymmetry and lateral/directional instability by decoupling of forebody and wing vortices was studied on a generic chine forebody/ 60 deg. delta configuration in the NASA Langley 7 by 10 foot High Speed Tunnel. The decoupling technique involved inboard leading edge flaps of varying span and deflection angle. Six component force/moment characteristics, surface pressure distributions and vapor-screen flow visualizations were acquired, on the basic wing-body configuration and with both single and twin vertical tails at M sub infinity = 0.1 and 0.4, and in the range alpha = 0 to 50 deg and beta = -10 to +10 degs. Results are presented which highlight the potential of vortex decoupling via leading edge flaps for enhanced high alpha lateral/directional characteristics.

Dual-energy-X-ray imaging to measure phase volume fractions in a transient multiphase flow

NASA Astrophysics Data System (ADS)

Loewen, Eric Paul

1999-12-01

The objective of this research was to visualize the pre-mixing phase of a fuel-coolant interaction (FCI) by using combinations of high-speed cinematography and dual energy X-ray imaging to identify and quantify the spatial and temporal characteristics of the three FCI phases---metal (fuel), liquid (coolant water), and voids (generated steam). (1) The high-speed cinematography imaging subsystem and the low-energy X-ray imaging subsystem provided visual photographs and distinguished generated voids from water. (2) The high-energy X-Ray imaging subsystem provided additional discernment of metal from water and vapor. This is the first time that dynamic dual X-ray images have been provided with quantitative results. The data provide new information concerning the melt fractions, melt jet configuration, melt jet velocity, and qualitative spatial and temporal quantification of the pre-mixing event. This information provides new insight into the FCI phenomenon that could not have been deduced from visible-light imaging or other instrumentation such as thermocouples, void sensors, or pressure transmitters. Significant findings include: (1) the fuel column (molten Pb jet) penetrated deeply (<7 cm) into the coolant (water) while maintaining its columnar shape. (2) Energetic FCIs occurred (and were imaged) below the melt-coolant interface temperature equal to the homogenous nucleation temperature (310°C). (3) The molten jet breakup was observed to be caused by hydrodynamic forces. (4) The Pb/water thermal interaction zone was imaged over melt temperatures from 330°C to 640°C and coolant subcooling of 4°C to 80°C. (5) The interface regions between the molten Pb and coolant was observed to grow with decreasing coolant subcooling. This imaging process can be applied to further study of the FCI phenomena at other test facilities. It can also be applied for observation of other two- or three-phase flow phenomena previously opaque to conventional imaging systems.

Frequency domain analysis of knock images

NASA Astrophysics Data System (ADS)

Qi, Yunliang; He, Xin; Wang, Zhi; Wang, Jianxin

2014-12-01

High speed imaging-based knock analysis has mainly focused on time domain information, e.g. the spark triggered flame speed, the time when end gas auto-ignition occurs and the end gas flame speed after auto-ignition. This study presents a frequency domain analysis on the knock images recorded using a high speed camera with direct photography in a rapid compression machine (RCM). To clearly visualize the pressure wave oscillation in the combustion chamber, the images were high-pass-filtered to extract the luminosity oscillation. The luminosity spectrum was then obtained by applying fast Fourier transform (FFT) to three basic colour components (red, green and blue) of the high-pass-filtered images. Compared to the pressure spectrum, the luminosity spectra better identify the resonant modes of pressure wave oscillation. More importantly, the resonant mode shapes can be clearly visualized by reconstructing the images based on the amplitudes of luminosity spectra at the corresponding resonant frequencies, which agree well with the analytical solutions for mode shapes of gas vibration in a cylindrical cavity.

Impact of the Ability to Divide Attention on Reading Performance in Glaucoma.

PubMed

Swenor, Bonnielin K; Varadaraj, Varshini; Dave, Paulomi; West, Sheila K; Rubin, Gary S; Ramulu, Pradeep Y

2017-05-01

To determine if the ability to divide attention affects the relationship between glaucoma-related vision loss and reading speed. Better eye mean deviation (MD), contrast sensitivity (CS), and better-eye distance visual acuity (VA) were measured in 28 participants with glaucoma and 21 controls. Reading speeds were assessed using MNRead, IRest, and sustained silent reading tests (words per minute, wpm). The ability to divide attention was measured using the Brief Test of Attention (BTA; scored 0-10). Multivariable linear regression models were used to determine the relationship between visual factors and reading speeds. Effect modification by BTA score (low BTA: <7; high BTA: ≥7) was examined. Worse CS (per 0.1 log unit) was associated with slower maximum reading speed on MNRead test for participants with low BTA scores (β = -9 wpm; 95% confidence interval [CI]: -16, -2), but not for those with high BTA scores (β = -2 wpm; 95% CI: -6, +2). Similarly, for the IRest test, worse CS was associated with slower reading speeds (β = -12 wpm; 95% CI: -20, -4) among those with low, but not high BTA scores (β = -4 wpm; 95% CI: -10, +2). For the sustained silent reading test, glaucoma status (versus controls), worse visual field (VF) MD (per 5 dB), and worse CS were associated with 39%, 21%, and 19% slower reading speeds, respectively, for those with low BTA scores (P < 0.05), but these associations were not significant among those with high BTA scores (P > 0.1 for all). Decreased ability to divide attention, indicated by lower BTA scores, is associated with slower reading speeds in glaucoma with reduced CS and VF defects.

Impact of the Ability to Divide Attention on Reading Performance in Glaucoma

PubMed Central

Swenor, Bonnielin K.; Varadaraj, Varshini; Dave, Paulomi; West, Sheila K.; Rubin, Gary S.; Ramulu, Pradeep Y.

2017-01-01

Purpose To determine if the ability to divide attention affects the relationship between glaucoma-related vision loss and reading speed. Methods Better eye mean deviation (MD), contrast sensitivity (CS), and better-eye distance visual acuity (VA) were measured in 28 participants with glaucoma and 21 controls. Reading speeds were assessed using MNRead, IRest, and sustained silent reading tests (words per minute, wpm). The ability to divide attention was measured using the Brief Test of Attention (BTA; scored 0–10). Multivariable linear regression models were used to determine the relationship between visual factors and reading speeds. Effect modification by BTA score (low BTA: <7; high BTA: ≥7) was examined. Results Worse CS (per 0.1 log unit) was associated with slower maximum reading speed on MNRead test for participants with low BTA scores (β = −9 wpm; 95% confidence interval [CI]: −16, −2), but not for those with high BTA scores (β = −2 wpm; 95% CI: −6, +2). Similarly, for the IRest test, worse CS was associated with slower reading speeds (β = −12 wpm; 95% CI: −20, −4) among those with low, but not high BTA scores (β = −4 wpm; 95% CI: −10, +2). For the sustained silent reading test, glaucoma status (versus controls), worse visual field (VF) MD (per 5 dB), and worse CS were associated with 39%, 21%, and 19% slower reading speeds, respectively, for those with low BTA scores (P < 0.05), but these associations were not significant among those with high BTA scores (P > 0.1 for all). Conclusions Decreased ability to divide attention, indicated by lower BTA scores, is associated with slower reading speeds in glaucoma with reduced CS and VF defects. PMID:28460047

Experimental Visualizations of a Generic Launch Vehicle Flow Field: Time-Resolved Shadowgraph and Infrared Imaging

NASA Technical Reports Server (NTRS)

Garbeff, Theodore J., II; Panda, Jayanta; Ross, James C.

2017-01-01

Time-Resolved shadowgraph and infrared (IR) imaging were performed to investigate off-body and on-body flow features of a generic, 'hammer-head' launch vehicle geometry previously tested by Coe and Nute (1962). The measurements discussed here were one part of a large range of wind tunnel test techniques that included steady-state pressure sensitive paint (PSP), dynamic PSP, unsteady surface pressures, and unsteady force measurements. Image data was captured over a Mach number range of 0.6 less than or equal to M less than or equal to 1.2 at a Reynolds number of 3 million per foot. Both shadowgraph and IR imagery were captured in conjunction with unsteady pressures and forces and correlated with IRIG-B timing. High-speed shadowgraph imagery was used to identify wake structure and reattachment behind the payload fairing of the vehicle. Various data processing strategies were employed and ultimately these results correlated well with the location and magnitude of unsteady surface pressure measurements. Two research grade IR cameras were positioned to image boundary layer transition at the vehicle nose and flow reattachment behind the payload fairing. The poor emissivity of the model surface treatment (fast PSP) proved to be challenging for the infrared measurement. Reference image subtraction and contrast limited adaptive histogram equalization (CLAHE) were used to analyze this dataset. Ultimately turbulent boundary layer transition was observed and located forward of the trip dot line at the model sphere-cone junction. Flow reattachment location was identified behind the payload fairing in both steady and unsteady thermal data. As demonstrated in this effort, recent advances in high-speed and thermal imaging technology have modernized classical techniques providing a new viewpoint for the modern researcher

Flow visualization for investigating stator losses in a multistage axial compressor

NASA Astrophysics Data System (ADS)

Smith, Natalie R.; Key, Nicole L.

2015-05-01

The methodology and implementation of a powder-paint-based flow visualization technique along with the illuminated flow physics are presented in detail for application in a three-stage axial compressor. While flow visualization often accompanies detailed studies, the turbomachinery literature lacks a comprehensive study which both utilizes flow visualization to interrupt the flow field and explains the intricacies of execution. Lessons learned for obtaining high-quality images of surface flow patterns are discussed in this study. Fluorescent paint is used to provide clear, high-contrast pictures of the recirculation regions on shrouded vane rows. An edge-finding image processing procedure is implemented to provide a quantitative measure of vane-to-vane variability in flow separation, which is approximately 7 % of the suction surface length for Stator 1. Results include images of vane suction side corner separations from all three stages at three loading conditions. Additionally, streakline patterns obtained experimentally are compared with those calculated from computational models. Flow physics associated with vane clocking and increased rotor tip clearance and their implications to stator loss are also investigated with this flow visualization technique. With increased rotor tip clearance, the vane surface flow patterns show a shift to larger separations and more radial flow at the tip. Finally, the effects of instrumentation on the flow field are highlighted.

Aeropropulsion Technology (APT). Task 23 - Stator Seal Cavity Flow Investigation

NASA Technical Reports Server (NTRS)

Heidegger, N. J.; Hall, E. J.; Delaney, R. A.

1996-01-01

The focus of NASA Contract NAS3-25950 Task 23 was to numerically investigate the flow through an axial compressor inner-banded stator seal cavity. The Allison/NASA developed ADPAC code was used to obtain all flow predictions. Flow through a labyrinth stator seal cavity of a high-speed compressor was modeled by coupling the cavity flow path and the main flow path of the compressor. A grid resolution study was performed to guarantee adequate grid spacing was used. Both unsteady rotor-stator-rotor interactions and steady-state isolated blade calculations were performed with and without the seal cavity present. A parameterized seal cavity study of the high-speed stator seal cavity collected a series of solutions for geometric variations. The parameter list included seal tooth gap, cavity depth, wheel speed, radial mismatch of hub flowpath, axial trench gap, hub corner treatments, and land edge treatments. Solution data presented includes radial and pitchwise distributions of flow variables and particle traces describing the flow character.

As time passes by: Observed motion-speed and psychological time during video playback.

PubMed

Nyman, Thomas Jonathan; Karlsson, Eric Per Anders; Antfolk, Jan

2017-01-01

Research shows that psychological time (i.e., the subjective experience and assessment of the passage of time) is malleable and that the central nervous system re-calibrates temporal information in accordance with situational factors so that psychological time flows slower or faster. Observed motion-speed (e.g., the visual perception of a rolling ball) is an important situational factor which influences the production of time estimates. The present study examines previous findings showing that observed slow and fast motion-speed during video playback respectively results in over- and underproductions of intervals of time. Here, we investigated through three separate experiments: a) the main effect of observed motion-speed during video playback on a time production task and b) the interactive effect of the frame rate (frames per second; fps) and motion-speed during video playback on a time production task. No main effect of video playback-speed or interactive effect between video playback-speed and frame rate was found on time production.

As time passes by: Observed motion-speed and psychological time during video playback

PubMed Central

Karlsson, Eric Per Anders; Antfolk, Jan

2017-01-01

Research shows that psychological time (i.e., the subjective experience and assessment of the passage of time) is malleable and that the central nervous system re-calibrates temporal information in accordance with situational factors so that psychological time flows slower or faster. Observed motion-speed (e.g., the visual perception of a rolling ball) is an important situational factor which influences the production of time estimates. The present study examines previous findings showing that observed slow and fast motion-speed during video playback respectively results in over- and underproductions of intervals of time. Here, we investigated through three separate experiments: a) the main effect of observed motion-speed during video playback on a time production task and b) the interactive effect of the frame rate (frames per second; fps) and motion-speed during video playback on a time production task. No main effect of video playback-speed or interactive effect between video playback-speed and frame rate was found on time production. PMID:28614353

An approach to instrument qualified visual range

NASA Astrophysics Data System (ADS)

Courtade, Benoît; Bonnet, Jordan; Woodruff, Chris; Larson, Josiah; Giles, Andrew; Sonde, Nikhil; Moore, C. J.; Schimon, David; Harris, David Money; Pond, Duane; Way, Scott

2008-04-01

This paper describes a system that calculates aircraft visual range with instrumentation alone. A unique message is encoded using modified binary phase shift keying and continuously flashed at high speed by ALSF-II runway approach lights. The message is sampled at 400 frames per second by an aircraft borne high-speed camera. The encoding is designed to avoid visible flicker and minimize frame rate. Instrument qualified visual range is identified as the largest distance at which the aircraft system can acquire and verify the correct, runway-specific signal. Scaled testing indicates that if the system were implemented on one full ALSF-II fixture, instrument qualified range could be established at 5 miles in clear weather conditions.

Plasma motion in the Venus ionosphere: Transition to supersonic flow

DOE Office of Scientific and Technical Information (OSTI.GOV)

Whitten, R.C.; Barnes, A.; McCormick, P.T.

1991-07-01

A remarkable feature of the ionosphere of Venus is the presence of nightward supersonic flows at high altitude near the terminator. In general the steady flow of an ideal gas admits a subsonic-supersonic transition only in the presence of special conditions, such as a convergence of the flow followed by divergence, or external forces. In this paper, the authors show that the relatively high pressure dayside plasma wells up slowly, and at high altitude it is accelerated horizontally through a relatively constricted region near the terminator toward the low-density nightside. In effect, the plasma flows through a nozzle that ismore » first converging, then diverging, permitting the transition to supersonic flow. Analysis of results from previously published models of the plasma flow in the upper ionosphere of Venus shows how such a nozzle is formed. The model plasma does indeed accelerate to supersonic speeds, reaching sonic speed just behind the terminator. The computed speeds prove to be close to those observed by the Pioneer Venus orbiter, and the ion transport rates are sufficient to produce and maintain the nightside ionosphere.« less

Two-phase flow characteristics of liquid nitrogen in vertically upward 0.5 and 1.0 mm micro-tubes: Visualization studies

NASA Astrophysics Data System (ADS)

Zhang, P.; Fu, X.

2009-10-01

Application of liquid nitrogen to cooling is widely employed in many fields, such as cooling of the high temperature superconducting devices, cryosurgery and so on, in which liquid nitrogen is generally forced to flow inside very small passages to maintain good thermal performance and stability. In order to have a full understanding of the flow and heat transfer characteristics of liquid nitrogen in micro-tube, high-speed digital photography was employed to acquire the typical two-phase flow patterns of liquid nitrogen in vertically upward micro-tubes of 0.531 and 1.042 mm inner diameters. It was found from the experimental results that the flow patterns were mainly bubbly flow, slug flow, churn flow and annular flow. And the confined bubble flow, mist flow, bubble condensation and flow oscillation were also observed. These flow patterns were characterized in different types of flow regime maps. The surface tension force and the size of the diameter were revealed to be the major factors affecting the flow pattern transitions. It was found that the transition boundaries of the slug/churn flow and churn/annular flow of the present experiment shifted to lower superficial vapor velocity; while the transition boundary of the bubbly/slug flow shifted to higher superficial vapor velocity compared to the results of the room-temperature fluids in the tubes with the similar hydraulic diameters. The corresponding transition boundaries moved to lower superficial velocity when reducing the inner diameter of the micro-tubes. Time-averaged void fraction and heat transfer characteristics for individual flow patterns were presented and special attention was paid to the effect of the diameter on the variation of void fraction.

V-ONSET: Introducing turbulent multiphase flow facility focusing on Lagrangian interfacial transfer dynamics

NASA Astrophysics Data System (ADS)

Salibindla, Ashwanth; Masuk, Ashik Ullah Mohammad; Ni, Rui

2017-11-01

We have designed and constructed a new vertical water tunnel, V-ONSET, to investigate interfacial mass, momentum and energy transfer between two phases in a Lagrangian frame. This system features an independent control of mean flow and turbulence level. The mean flow opposes the rising/falling velocity of the second phase, ``suspending'' the particles and increasing tracking time in the view area. Strong turbulence is generated by shooting 88 digitally-controlled water jets into the test section. The second phase, either bubbles or oil droplets, can be introduced into the test section through a capillary island. In addition to this flow control system, V-ONSET comes with a 3D two-phase visualization system, consisting of high-speed cameras, two-colored LED system, and in-house Lagrangian particle tracking algorithm. This enables us to acquire the Lagrangian evolution of both phases and the interfacial transfer dynamics in between, paving the way for new closure models for two-phase simulations. Financial support for this project was provided by National Science Foundation under Grant Number: 1653389 and 1705246.

Boundary Layer Flow Control with a One Atmosphere Uniform Glow Discharge Surface Plasma

NASA Technical Reports Server (NTRS)

Roth, J. Reece; Sherman, Daniel M.; Wilkinson, Stephen P.

1998-01-01

Low speed wind tunnel data have been acquired for planar panels covered by a uniform, glow-discharge surface plasma in atmospheric pressure air known as the One Atmosphere Uniform Glow Discharge Plasma (OAUGDP). Streamwise and spanwise arrays of flush, plasma-generating surface electrodes have been studied in laminar, transitional, and fully turbulent boundary layer flow. Plasma between symmetric streamwise electrode strips caused large increases in panel drag, whereas asymmetric spanwise electrode configurations produced a significant thrust. Smoke wire flow visualization and mean velocity diagnostics show the primary cause of the phenomena to be a combination of mass transport and vortical structures induced by strong paraelectric ElectroHydroDynamic (EHD) body forces on the flow.

Small axial compressor technology, volume 1

NASA Technical Reports Server (NTRS)

Holman, F. F.; Kidwell, J. R.; Ware, T. C.

1976-01-01

A scaled single-stage, highly-loaded, axial-flow transonic compressor was tested at speeds from 70 to 110% design equivalent speed to evaluate the effects of scaling compromises and the individual and combined effects of rotor tip running clearance and rotor shroud casing treatment on the overall and blade element performance. At design speed and 1% tip clearance the stage demonstrated an efficiency of 83.2% at 96.4% design flow and a pressure ratio of 1.865. Casing treatment increased design speed surge margin 2.0 points to 12.8%. Overall performance was essentially unchanged. An increase in rotor running clearance to 2.2%, with smooth casing, reduced design speed peak efficiency 5.7 points, flow by 7.4%, pressure ratio to 1.740, and surge margin to 5.4%. Reinstalling casing treatment regained 3.5 points in design speed peak efficiency, 4.7% flow, increased pressure ratio to 1.800 and surge margin to 8.7%.

The status of analytical preparation for 2-dimensional testing at high transonic speeds in the University of Southampton transonic self-streamlining wind tunnel

NASA Technical Reports Server (NTRS)

Lewis, M. C.

1984-01-01

Validation data from the Transonic Self-Streamlining Wind Tunnel has proved the feasibility of streamlining two dimensional flexible walls at low speeds and up to transonic speeds, the upper limit being the speed where the flexible walls are just supercritical. At this condition, breakdown of the wall setting strategy is evident in that convergence is neither as rapid nor as stable as for lower speeds, and wall streamlining criteria are not always completely satisfied. The only major step necessary to permit the extension of two dimensional testing into higher transonic speeds is the provision of a rapid algorithm to solve for mixed flow in the imagery flow fields. The status of two dimensional high transonic testing in the Transonic Self-Streamlining Wind Tunnel is outlined and, in particular, the progress of adapting an algorithm, which solves the Transonic Small Perturbation Equation, for predicting the imagery flow fields is detailed.

Criterion for Identifying Vortices in High-Pressure Flows

NASA Technical Reports Server (NTRS)

Bellan, Josette; Okong'o, Nora

2007-01-01

A study of four previously published computational criteria for identifying vortices in high-pressure flows has led to the selection of one of them as the best. This development can be expected to contribute to understanding of high-pressure flows, which occur in diverse settings, including diesel, gas turbine, and rocket engines and the atmospheres of Jupiter and other large gaseous planets. Information on the atmospheres of gaseous planets consists mainly of visual and thermal images of the flows over the planets. Also, validation of recently proposed computational models of high-pressure flows entails comparison with measurements, which are mainly of visual nature. Heretofore, the interpretation of images of high-pressure flows to identify vortices has been based on experience with low-pressure flows. However, high-pressure flows have features distinct from those of low-pressure flows, particularly in regions of high pressure gradient magnitude caused by dynamic turbulent effects and by thermodynamic mixing of chemical species. Therefore, interpretations based on low-pressure behavior may lead to misidentification of vortices and other flow structures in high-pressure flows. The study reported here was performed in recognition of the need for one or more quantitative criteria for identifying coherent flow structures - especially vortices - from previously generated flow-field data, to complement or supersede the determination of flow structures by visual inspection of instantaneous fields or flow animations. The focus in the study was on correlating visible images of flow features with various quantities computed from flow-field data.

Fluid dynamic mechanisms and interactions within separated flows

NASA Astrophysics Data System (ADS)

Dutton, J. C.; Addy, A. L.

1990-02-01

The significant results of a joint research effort investigating the fundamental fluid dynamic mechanisms and interactions within high-speed separated flows are presented in detail. The results have obtained through analytical and numerical approaches, but with primary emphasis on experimental investigations of missile and projectile base flow-related configurations. The objectives of the research program focus on understanding the component mechanisms and interactions which establish and maintain high-speed separated flow regions. The analytical and numerical efforts have centered on unsteady plume-wall interactions in rocket launch tubes and on predictions of the effects of base bleed on transonic and supersonic base flowfields. The experimental efforts have considered the development and use of a state-of-the-art two component laser Doppler velocimeter (LDV) system for experiments with planar, two-dimensional, small-scale models in supersonic flows. The LDV experiments have yielded high quality, well documented mean and turbulence velocity data for a variety of high-speed separated flows including initial shear layer development, recompression/reattachment processes for two supersonic shear layers, oblique shock wave/turbulent boundary layer interactions in a compression corner, and two-stream, supersonic, near-wake flow behind a finite-thickness base.

Experimental studying of local characteristics of gas-liquid flow in microchannels by optical methods

NASA Astrophysics Data System (ADS)

Bartkus, German V.; Kuznetsov, Vladimir V.

2018-03-01

The local characteristics of the gas-liquid two-phase flow in rectangular microchannels 420 × 280 μm and 395 × 205 μm with T-shaped mixer inlet were experimentally investigated in this work. Visualization of flow regimes and measurement of local characteristics were carried out using a high-speed video camera Optronis CX600x2 and laser-induced fluorescence (LIF) method. Deionized water and ethanol were used as the liquid phase, and nitrogen - as the gas phase. The Rhodamine 6G dye was added to the liquid. The location of the microchannel in space (horizontal, vertical) was changed. The profiles of the liquid film along the long side of the microchannel were obtained, the local film thickness was measured in the channel`s central section for the elongated bubble flow and the transition flow of the deionized water-nitrogen mixture. The unevenness of liquid film thickness at the channel cross-section and along the bubble was experimentally shown. The temporal dynamics of two-phase flow for the ethanol-nitrogen mixture was shown. It was found that most of the liquid flows in the meniscus on the short side of the microchannel for the present gas and liquid flow rates.

Numerical investigation of cylinder wake flow with a rear stagnation jet

NASA Astrophysics Data System (ADS)

Mo, J. D.; Duke, M. R., Jr.

1994-05-01

Upon visualization of the flow past a cylinder with a rear stagnation jet (RSJ), the flow appears fully attached as conventional inviscid flow does. Therefore, at first glance, it would be suspected that the form drag on the cylinder has been reduced to zero as predicted by inviscid flow theory. However, a detailed numerical simulation reveals that the form drag coefficient increases as the jet velocity increases. The mechanics of the increasing form drag are addressed. The following conclusions were drawn: (1) flow behind a cylinder can be effectively influenced by a RSJ; (2) the unsymmetric wake flow becomes symmetric when the RSI is in operation with a velocity ratio as low as 1; the size of the symmetric recirculation region becomes smaller as the jet speed increases; (3) a RSJ forces a symmetrical wake flow pattern, thus eliminating the lateral force; (4) the pressure on the cylinder surface decreases over the entire surface, but significantly more on the downstream side of the cylinder, as the jet velocity increases, causing an increase in form drag as jet velocity ratio increases; and (5) the RSJ to significantly increase form drag on a bluff body has direct applications in aerodynamic controls of reentry or fligths at high angles of attack.

Universal Visual Features Might Be Necessary for Fluent Reading. A Longitudinal Study of Visual Reading in Braille and Cyrillic Alphabets

PubMed Central

Bola, Łukasz; Radziun, Dominika; Siuda-Krzywicka, Katarzyna; Sowa, Joanna E.; Paplińska, Małgorzata; Sumera, Ewa; Szwed, Marcin

2017-01-01

It has been hypothesized that efficient reading is possible because all reading scripts have been matched, through cultural evolution, to the natural capabilities of the visual cortex. This matching has resulted in all scripts being made of line-junctions, such as T, X, or L. Our aim was to test a critical prediction of this hypothesis: visual reading in an atypical script that is devoid of line-junctions (such as the Braille alphabet read visually) should be much less efficient than reading in a “normal” script (e.g., Cyrillic). Using a lexical decision task, we examined Visual Braille reading speed and efficiency in sighted Braille teachers. As a control, we tested learners of a natural visual script, Cyrillic. Both groups participated in a two semester course of either visual Braille or Russian while their reading speed and accuracy was tested at regular intervals. The results show that visual Braille reading is slow, prone to errors and highly serial, even in Braille readers with years of prior reading experience. Although subjects showed some improvements in their visual Braille reading accuracy and speed following the course, the effect of word length on reading speed (typically observed in beginning readers) was remained very sizeable through all testing sessions. These results are in stark contrast to Cyrillic, a natural script, where only 3 months of learning were sufficient to achieve relative proficiency. Taken together, these results suggest that visual features such as line junctions and their combinations might be necessary for efficient reading. PMID:28421027

Universal Visual Features Might Be Necessary for Fluent Reading. A Longitudinal Study of Visual Reading in Braille and Cyrillic Alphabets.

PubMed

Bola, Łukasz; Radziun, Dominika; Siuda-Krzywicka, Katarzyna; Sowa, Joanna E; Paplińska, Małgorzata; Sumera, Ewa; Szwed, Marcin

2017-01-01

It has been hypothesized that efficient reading is possible because all reading scripts have been matched, through cultural evolution, to the natural capabilities of the visual cortex. This matching has resulted in all scripts being made of line-junctions, such as T, X, or L. Our aim was to test a critical prediction of this hypothesis: visual reading in an atypical script that is devoid of line-junctions (such as the Braille alphabet read visually) should be much less efficient than reading in a "normal" script (e.g., Cyrillic). Using a lexical decision task, we examined Visual Braille reading speed and efficiency in sighted Braille teachers. As a control, we tested learners of a natural visual script, Cyrillic. Both groups participated in a two semester course of either visual Braille or Russian while their reading speed and accuracy was tested at regular intervals. The results show that visual Braille reading is slow, prone to errors and highly serial, even in Braille readers with years of prior reading experience. Although subjects showed some improvements in their visual Braille reading accuracy and speed following the course, the effect of word length on reading speed (typically observed in beginning readers) was remained very sizeable through all testing sessions. These results are in stark contrast to Cyrillic, a natural script, where only 3 months of learning were sufficient to achieve relative proficiency. Taken together, these results suggest that visual features such as line junctions and their combinations might be necessary for efficient reading.

Nearly Interactive Parabolized Navier-Stokes Solver for High Speed Forebody and Inlet Flows

NASA Technical Reports Server (NTRS)

Benson, Thomas J.; Liou, May-Fun; Jones, William H.; Trefny, Charles J.

2009-01-01

A system of computer programs is being developed for the preliminary design of high speed inlets and forebodies. The system comprises four functions: geometry definition, flow grid generation, flow solver, and graphics post-processor. The system runs on a dedicated personal computer using the Windows operating system and is controlled by graphical user interfaces written in MATLAB (The Mathworks, Inc.). The flow solver uses the Parabolized Navier-Stokes equations to compute millions of mesh points in several minutes. Sample two-dimensional and three-dimensional calculations are demonstrated in the paper.

Supersonic turbulent boundary layers with periodic mechanical non-equilibrium

NASA Astrophysics Data System (ADS)

Ekoto, Isaac Wesley

Previous studies have shown that favorable pressure gradients reduce the turbulence levels and length scales in supersonic flow. Wall roughness has been shown to reduce the large-scales in wall bounded flow. Based on these previous observations new questions have been raised. The fundamental questions this dissertation addressed are: (1) What are the effects of wall topology with sharp versus blunt leading edges? and (2) Is it possible that a further reduction of turbulent scales can occur if surface roughness and favorable pressure gradients are combined? To answer these questions and to enhance the current experimental database, an experimental analysis was performed to provide high fidelity documentation of the mean and turbulent flow properties along with surface and flow visualizations of a high-speed (M = 2.86), high Reynolds number (Retheta ≈ 60,000) supersonic turbulent boundary layer distorted by curvature-induced favorable pressure gradients and large-scale ( k+s ≈ 300) uniform surface roughness. Nine models were tested at three separate locations. Three pressure gradient models strengths (a nominally zero, a weak, and a strong favorable pressure gradient) and three roughness topologies (aerodynamically smooth, square, and diamond shaped roughness elements) were used. Highly resolved planar measurements of mean and fluctuating velocity components were accomplished using particle image velocimetry. Stagnation pressure profiles were acquired with a traversing Pitot probe. Surface pressure distributions were characterized using pressure sensitive paint. Finally flow visualization was accomplished using schlieren photographs. Roughness topology had a significant effect on the boundary layer mean and turbulent properties due to shock boundary layer interactions. Favorable pressure gradients had the expected stabilizing effect on turbulent properties, but the improvements were less significant for models with surface roughness near the wall due to increased tendency towards flow separation. It was documented that proper roughness selection coupled with a sufficiently strong favorable pressure gradient produced regions of "negative" production in the transport of turbulent stress. This led to localized areas of significant turbulence stress reduction. With proper roughness selection and sufficient favorable pressure gradient strength, it is believed that localized relaminarization of the boundary layer is possible.

Numerical Speed of Sound and its Application to Schemes for all Speeds

NASA Technical Reports Server (NTRS)

Liou, Meng-Sing; Edwards, Jack R.

1999-01-01

The concept of "numerical speed of sound" is proposed in the construction of numerical flux. It is shown that this variable is responsible for the accurate resolution of' discontinuities, such as contacts and shocks. Moreover, this concept can he readily extended to deal with low speed and multiphase flows. As a results, the numerical dissipation for low speed flows is scaled with the local fluid speed, rather than the sound speed. Hence, the accuracy is enhanced the correct solution recovered, and the convergence rate improved. We also emphasize the role of mass flux and analyze the behavior of this flux. Study of mass flux is important because the numerical diffusivity introduced in it can be identified. In addition, it is the term common to all conservation equations. We show calculated results for a wide variety of flows to validate the effectiveness of using the numerical speed of sound concept in constructing the numerical flux. We especially aim at achieving these two goals: (1) improving accuracy and (2) gaining convergence rates for all speed ranges. We find that while the performance at high speed range is maintained, the flux now has the capability of performing well even with the low: speed flows. Thanks to the new numerical speed of sound, the convergence is even enhanced for the flows outside of the low speed range. To realize the usefulness of the proposed method in engineering problems, we have also performed calculations for complex 3D turbulent flows and the results are in excellent agreement with data.

Pulsed photoacoustic flow imaging with a handheld system

NASA Astrophysics Data System (ADS)

van den Berg, Pim J.; Daoudi, Khalid; Steenbergen, Wiendelt

2016-02-01

Flow imaging is an important technique in a range of disease areas, but estimating low flow speeds, especially near the walls of blood vessels, remains challenging. Pulsed photoacoustic flow imaging can be an alternative since there is little signal contamination from background tissue with photoacoustic imaging. We propose flow imaging using a clinical photoacoustic system that is both handheld and portable. The system integrates a linear array with 7.5 MHz central frequency in combination with a high-repetition-rate diode laser to allow high-speed photoacoustic imaging-ideal for this application. This work shows the flow imaging performance of the system in vitro using microparticles. Both two-dimensional (2-D) flow images and quantitative flow velocities from 12 to 75 mm/s were obtained. In a transparent bulk medium, flow estimation showed standard errors of ˜7% the estimated speed; in the presence of tissue-realistic optical scattering, the error increased to 40% due to limited signal-to-noise ratio. In the future, photoacoustic flow imaging can potentially be performed in vivo using fluorophore-filled vesicles or with an improved setup on whole blood.

A cellular automata traffic flow model for three-phase theory

NASA Astrophysics Data System (ADS)

Qian, Yong-Sheng; Feng, Xiao; Zeng, Jun-Wei

2017-08-01

This paper presents a newly-modified KKW model including the subdivided vehicles types, and introduces the changes for a driver's sensitivity into the speed fluctuation. By means of the numerical simulation the following conclusions are obtained herewith: 1. Velocity disturbance propagation in traffic flow is caused by the speed adaptation among vehicles. 2. In free flow phase, very fewer vehicles are affected by the velocity disturbance and the effect can be dissipated quickly thus the time of disturbance in a single vehicle is quite shorter. On the contrary, the impact duration time of the disturbance on a single vehicle is longer in synchronous flow phase, thus, it will affect more vehicles accordingly. 3. Under the free flow phase, the continuous deceleration behavior of a high speed vehicle to adapt the preceding car with slow speed can cause the reduction of the driver's sensitivity, lead to the vehicle over-deceleration and aggravate the effects of velocity perturbations While in the synchronous flow phase, though the reaction delay caused by the driver's sensitivity reduction can induce speed wave dissolving in essence, it increases the impact of disturbance on the traffic flow. 4. The large acceleration and deceleration tendency of an aggressive driver in the free flow phase always increase the influence of the velocity disturbance, while a conservative driver often weakens the influence. However, in the synchronized flow, since the high traffic density and the synchronization between vehicles is very strong, also the main factor which affects the driver's speed choice is the distance among vehicles, therefore the effect of a driver's behavior tendency to the spread of velocity perturbation is not obvious under this state.

ULTRAHIGH SPEED SWEPT SOURCE OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY OF RETINAL AND CHORIOCAPILLARIS ALTERATIONS IN DIABETIC PATIENTS WITH AND WITHOUT RETINOPATHY.

PubMed

Choi, WooJhon; Waheed, Nadia K; Moult, Eric M; Adhi, Mehreen; Lee, ByungKun; De Carlo, Talisa; Jayaraman, Vijaysekhar; Baumal, Caroline R; Duker, Jay S; Fujimoto, James G

2017-01-01

To investigate the utility of ultrahigh speed, swept source optical coherence tomography angiography in visualizing retinal microvascular and choriocapillaris (CC) changes in diabetic patients. The study was prospective and cross-sectional. A 1,050 nm wavelength, 400 kHz A-scan rate swept source optical coherence tomography prototype was used to perform volumetric optical coherence tomography angiography of the retinal and CC vasculatures in diabetic patients and normal subjects. Sixty-three eyes from 32 normal subjects, 9 eyes from 7 patients with proliferative diabetic retinopathy, 29 eyes from 16 patients with nonproliferative diabetic retinopathy, and 51 eyes from 28 diabetic patients without retinopathy were imaged. Retinal and CC microvascular abnormalities were observed in all stages of diabetic retinopathy. In nonproliferative diabetic retinopathy and proliferative diabetic retinopathy, optical coherence tomography angiography visualized a variety of vascular abnormalities, including clustered capillaries, dilated capillary segments, tortuous capillaries, regions of capillary dropout, reduced capillary density, abnormal capillary loops, and foveal avascular zone enlargement. In proliferative diabetic retinopathy, retinal neovascularization above the inner limiting membrane was visualized. Regions of CC flow impairment in patients with proliferative diabetic retinopathy and nonproliferative diabetic retinopathy were also observed. In 18 of the 51 of eyes from diabetic patients without retinopathy, retinal mircrovascular abnormalities were observed and CC flow impairment was found in 24 of the 51 diabetic eyes without retinopathy. The ability of optical coherence tomography angiography to visualize retinal and CC microvascular abnormalities suggests it may be a useful tool for understanding pathogenesis, evaluating treatment response, and earlier detection of vascular abnormalities in patients with diabetes.

Creating drag and lift curves from soccer trajectories

NASA Astrophysics Data System (ADS)

Goff, John Eric; Kelley, John; Hobson, Chad M.; Seo, Kazuya; Asai, Takeshi; Choppin, S. B.

2017-07-01

Trajectory analysis is an alternative to using wind tunnels to measure a soccer ball’s aerodynamic properties. It has advantages over wind tunnel testing such as being more representative of game play. However, previous work has not presented a method that produces complete, speed-dependent drag and lift coefficients. Four high-speed cameras in stereo-calibrated pairs were used to measure the spatial co-ordinates for 29 separate soccer trajectories. Those trajectories span a range of launch speeds from 9.3 to 29.9 m s-1. That range encompasses low-speed laminar flow of air over a soccer ball, through the drag crises where air flow is both laminar and turbulent, and up to high-speed turbulent air flow. Results from trajectory analysis were combined to give speed-dependent drag and lift coefficient curves for the entire range of speeds found in the 29 trajectories. The average root mean square error between the measured and modelled trajectory was 0.028 m horizontally and 0.034 m vertically. The drag and lift crises can be observed in the plots of drag and lift coefficients respectively.

High speed turbulent reacting flows: DNS and LES

NASA Technical Reports Server (NTRS)

Givi, Peyman

1990-01-01

Work on understanding the mechanisms of mixing and reaction in high speed turbulent reacting flows was continued. Efforts, in particular, were concentrated on taking advantage of modern computational methods to simulate high speed turbulent flows. In doing so, two methodologies were used: large eddy simulations (LES) and direct numerical simulations (DNS). In the work related with LES the objective is to study the behavior of the probability density functions (pdfs) of scalar properties within the subgrid in reacting turbulent flows. The data base obtained by DNS for a detailed study of the pdf characteristics within the subgrid was used. Simulations are performed for flows under various initializations to include the effects of compressibility on mixing and chemical reactions. In the work related with DNS, a two-dimensional temporally developing high speed mixing layer under the influence of a second-order non-equilibrium chemical reaction of the type A + B yields products + heat was considered. Simulations were performed with different magnitudes of the convective Mach numbers and with different chemical kinetic parameters for the purpose of examining the isolated effects of the compressibility and the heat released by the chemical reactions on the structure of the layer. A full compressible code was developed and utilized, so that the coupling between mixing and chemical reactions is captured in a realistic manner.

The Roles of Beaconing and Dead Reckoning in Human Virtual Navigation

ERIC Educational Resources Information Center

Bodily, Kent D.; Daniel, Thomas A.; Sturz, Bradley R.

2012-01-01

Beaconing is a process in which the distance between a visual landmark and current position is reduced in order to return to a location. In contrast, dead reckoning is a process in which vestibular, kinesthetic and/or optic flow cues are utilized to update speed of movement, elapsed time of movement, and direction of movement to return to a…

Study of an array of two circular jets impinging on a flat surface

NASA Astrophysics Data System (ADS)

Simionescu, Ştefan-Mugur; Dhondoo, Nilesh; Bălan, Corneliu

2018-02-01

In this study, the flow characteristics of an array of two circular, laminar air jets impinging on a smooth solid wall are experimentally and numerically investigated. Direct visualizations using high speed/resolution camera are performed. The evolution of the vortical structures in the area where the jet is deflected from axial to radial direction is emphasized, as well as the interaction between the two jets. A set of CFD numerical simulations in 2D flow domains are performed by using the commercial software Fluent, in the context of Reynolds-averaged Navier-Stokes (RANS) modeling. The numerical resultsare compared and validated with the experiments. The vorticity number is computed and plotted at two different positions from the jet nozzle, and a study of its distribution gives a clue on how the jets are interacting with each other in the proximity of the solid wall.

Turbulence generation by waves

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kaftori, D.; Nan, X.S.; Banerjee, S.

The interaction between two-dimensional mechanically generated waves, and a turbulent stream was investigated experimentally in a horizontal channel, using a 3-D LDA synchronized with a surface position measuring device and a micro-bubble tracers flow visualization with high speed video. Results show that although the wave induced orbital motion reached all the way to the wall, the characteristics of the turbulence wall structures and the turbulence intensity close to the wall were not altered. Nor was the streaky nature of the wall layer. On the other hand, the mean velocity profile became more uniform and the mean friction velocity was increased.more » Close to the free surface, the turbulence intensity was substantially increased as well. Even in predominantly laminar flows, the introduction of 2-D waves causes three dimensional turbulence. The turbulence enhancement is found to be proportional to the wave strength.« less

Ray-based acoustic localization of cavitation in a highly reverberant environment.

PubMed

Chang, Natasha A; Dowling, David R

2009-05-01

Acoustic detection and localization of cavitation have inherent advantages over optical techniques because cavitation bubbles are natural sound sources, and acoustic transduction of cavitation sounds does not require optical access to the region of cavitating flow. In particular, near cavitation inception, cavitation bubbles may be visually small and occur infrequently, but may still emit audible sound pulses. In this investigation, direct-path acoustic recordings of cavitation events are made with 16 hydrophones mounted on the periphery of a water tunnel test section containing a low-cavitation-event-rate vortical flow. These recordings are used to localize the events in three dimensions via cross correlations to obtain arrival time differences. Here, bubble localization is hindered by reverberation, background noise, and the fact that both the pulse emission time and waveform are unknown. These hindrances are partially mitigated by a signal-processing scheme that incorporates straight-ray acoustic propagation and Monte-Carlo techniques for compensating ray-path, sound-speed, and hydrophone-location uncertainties. The acoustic localization results are compared to simultaneous optical localization results from dual-camera high-speed digital-video recordings. For 53 bubbles and a peak-signal to noise ratio frequency of 6.7 kHz, the root-mean-square spatial difference between optical and acoustic bubble location results was 1.94 cm. Parametric dependences in acoustic localization performance are also presented.

Combustion behaviors of GO2/GH2 swirl-coaxial injector using non-intrusive optical diagnostics

NASA Astrophysics Data System (ADS)

GuoBiao, Cai; Jian, Dai; Yang, Zhang; NanJia, Yu

2016-06-01

This research evaluates the combustion behaviors of a single-element, swirl-coaxial injector in an atmospheric combustion chamber with gaseous oxygen and gaseous hydrogen (GO2/GH2) as the propellants. A brief simulated flow field schematic comparison between a shear-coaxial injector and the swirl-coaxial injector reveals the distribution characteristics of the temperature field and streamline patterns. Advanced optical diagnostics, i.e., OH planar laser-induced fluorescence and high-speed imaging, are simultaneously employed to determine the OH radical spatial distribution and flame fluctuations, respectively. The present study focuses on the flame structures under varying O/F mixing ratios and center oxygen swirl intensities. The combined use of several image-processing methods aimed at OH instantaneous images, including time-averaged, root-mean-square, and gradient transformation, provides detailed information regarding the distribution of the flow field. The results indicate that the shear layers anchored on the oxygen injector lip are the main zones of chemical heat release and that the O/F mixing ratio significantly affects the flame shape. Furthermore, with high-speed imaging, an intuitionistic ignition process and several consecutive steady-state images reveal that lean conditions make it easy to drive the combustion instabilities and that the center swirl intensity has a moderate influence on the flame oscillation strength. The results of this study provide a visualized analysis for future optimal swirl-coaxial injector designs.

Experiments on high speed ejectors

NASA Technical Reports Server (NTRS)

Wu, J. J.

1986-01-01

Experimental studies were conducted to investigate the flow and the performance of thrust augmenting ejectors for flight Mach numbers in the range of 0.5 to 0.8, primary air stagnation pressures up to 107 psig (738 kPa), and primary air stagnation temperatures up to 1250 F (677 C). The experiment verified the existence of the second solution ejector flow, where the flow after complete mixing is supersonic. Thrust augmentation in excess of 1.2 was demonstrated for both hot and cold primary jets. The experimental ejector performed better than the corresponding theoretical optimal first solution ejector, where the mixed flow is subsonic. Further studies are required to realize the full potential of the second solution ejector. The research program was started by the Flight Dynamics Research Corporation (FDRC) to investigate the characteristic of a high speed ejector which augments thrust of a jet at high flight speeds.

Visualization study of flow in axial flow inducer.

NASA Technical Reports Server (NTRS)

Lakshminarayana, B.

1972-01-01

A visualization study of the flow through a three ft dia model of a four bladed inducer, which is operated in air at a flow coefficient of 0.065, is reported in this paper. The flow near the blade surfaces, inside the rotating passages, downstream and upstream of the inducer is visualized by means of smoke, tufts, ammonia filament, and lampblack techniques. Flow is found to be highly three dimensional, with appreciable radial velocity throughout the entire passage. The secondary flows observed near the hub and annulus walls agree with qualitative predictions obtained from the inviscid secondary flow theory.

Experimental investigation of turbulent wall jet

NASA Astrophysics Data System (ADS)

Andre, Matthieu A.; Bardet, Philippe M.

2011-11-01

Water jet flowing on a flat plate surrounded by quiescent air constitutes a standard case for the study of the interaction between turbulence and the liquid-air interface. This is of particular interest in the understanding of heat and mass transfers across interfaces. The structure of the surface has a great influence on the rate of the transfers which is critical for chemical processes like separation or absorption; pool-type nuclear reactor; climate modeling etc. This study focuses on high Froude (8 to 12) and Weber (3300 to 7400) numbers at which the surface exhibits small wavelength and large amplitude deformations, such as ligaments, surface break up with air entrainment and droplets projection. The experiment features a high velocity (up to 7.5 m/s) water wall jet (19.05mm thick at the nozzle exit) flowing on a flat plate (Re =105 to 1 . 5 .105). High speed movies and PLIF visualization show the evolution of the surface from smooth to 2D structures, then 3D disturbances as the turbulence arising from the wall interacts with the surface.

Effect of Rheological Properties on Liquid Curtain Coating

NASA Astrophysics Data System (ADS)

Mohammad Karim, Alireza; Suszynski, Wieslaw; Griffith, William; Pujari, Saswati; Carvalho, Marcio; Francis, Lorraine; Dow Chemical Company Collaboration; PUC-Rio Collaboration

2017-11-01

Curtain coating is one of the preferred methods for high-speed precision application of single-layer and multi-layer coatings in technology. However, uniform coatings are only obtained in a certain range of operating parameters, called coating window. The two main physical mechanisms that limit successful curtain coating are liquid curtain breakup and air entrainment. The rheological properties of the liquid play an important role on these mechanisms, but the fundamental understanding of these relations is still not complete. The effect of rate-dependent shear and extensional viscosities on the stability of viscoelastic and shear thinning liquid curtains were explored by high-speed visualization. Aqueous solutions of polyethylene oxide (PEO) and polyethylene glycol (PEG) were used as viscoelastic liquids. Xanthan Gum in water and glycerol solutions with a range of compositions were used as shear thinning liquids. The critical condition was determined by examining flow rate below which curtain broke. In this work, we also analyze relative importance of rate-dependent shear and extensional viscosity on both curtain breakup and air entrainment. We would like to acknowledge the financial support from the Dow Chemical Company.

Walking Speed Influences the Effects of Implicit Visual Feedback Distortion on Modulation of Gait Symmetry

PubMed Central

Maestas, Gabrielle; Hu, Jiyao; Trevino, Jessica; Chunduru, Pranathi; Kim, Seung-Jae; Lee, Hyunglae

2018-01-01

The use of visual feedback in gait rehabilitation has been suggested to promote recovery of locomotor function by incorporating interactive visual components. Our prior work demonstrated that visual feedback distortion of changes in step length symmetry entails an implicit or unconscious adaptive process in the subjects’ spatial gait patterns. We investigated whether the effect of the implicit visual feedback distortion would persist at three different walking speeds (slow, self-preferred and fast speeds) and how different walking speeds would affect the amount of adaption. In the visual feedback distortion paradigm, visual vertical bars portraying subjects’ step lengths were distorted so that subjects perceived their step lengths to be asymmetric during testing. Measuring the adjustments in step length during the experiment showed that healthy subjects made spontaneous modulations away from actual symmetry in response to the implicit visual distortion, no matter the walking speed. In all walking scenarios, the effects of implicit distortion became more significant at higher distortion levels. In addition, the amount of adaptation induced by the visual distortion was significantly greater during walking at preferred or slow speed than at the fast speed. These findings indicate that although a link exists between supraspinal function through visual system and human locomotion, sensory feedback control for locomotion is speed-dependent. Ultimately, our results support the concept that implicit visual feedback can act as a dominant form of feedback in gait modulation, regardless of speed. PMID:29632481

Investigation of the effect of impeller speed on granules formed using a PMA-1 high shear granulator.

PubMed

Logan, R; Briens, L

2012-11-01

Impeller speed was varied from 300 to 1500 rpm during the wet high shear granulation of a placebo formulation using a new vertical shaft PharmaMATRIX-1 granulator. The resulting granules were extensively analysed for differences caused by the varying impeller speed with emphasis on flowability. Microscopy showed that initial granules were formed primarily from microcrystalline cellulose at all tested impeller speeds. At low impeller speed of 300 rpm in the "bumpy" flow regime, forces from the impeller were insufficient to incorporate all the components of the formulation into the granules and to promote granule growth to a size that significantly improved flowability. The "roping" flow regime at higher impeller speeds promoted granule growth to a median particle size of at least 100 µm that improved the flowability of the mixture. Particle size distribution measurements and advanced indicators based on avalanching behavior, however, showed that an impeller speed of 700 rpm produced the largest fraction of optimal granules with the best flowability potential. This impeller speed allowed good development of "roping" flow for sufficient mixing, collision rates and kinetic energy for collisions while minimizing excessive centrifugal forces that promote buildup around the bowl perimeter.

Three-dimensional modelling of thin liquid films over spinning disks

NASA Astrophysics Data System (ADS)

Zhao, Kun; Wray, Alex; Yang, Junfeng; Matar, Omar

2016-11-01

In this research the dynamics of a thin film flowing over a rapidly spinning, horizontal disk is considered. A set of non-axisymmetric evolution equations for the film thickness, radial and azimuthal flow rates are derived using a boundary-layer approximation in conjunction with the Karman-Polhausen approximation for the velocity distribution in the film. These highly nonlinear partial differential equations are then solved numerically in order to reveal the formation of two and three-dimensional large-amplitude waves that travel from the disk inlet to its periphery. The spatio-temporal profile of film thickness provides us with visualization of flow structures over the entire disk and by varying system parameters(volumetric flow rate of fluid and rotational speed of disk) different wave patterns can be observed, including spiral, concentric, smooth waves and wave break-up in exceptional conditions. Similar types of waves can be found by experimentalists in literature and CFD simulation and our results show good agreement with both experimental and CFD results. Furthermore, the semi-parabolic velocity profile assumed in our model under the waves is directly compared with CFD data in various flow regimes in order to validate our model. EPSRC UK Programme Grant EP/K003976/1.

Active Flow Control: Instrumentation Automation and Experimental Technique

NASA Technical Reports Server (NTRS)

Gimbert, N. Wes

1995-01-01

In investigating the potential of a new actuator for use in an active flow control system, several objectives had to be accomplished, the largest of which was the experimental setup. The work was conducted at the NASA Langley 20x28 Shear Flow Control Tunnel. The actuator named Thunder, is a high deflection piezo device recently developed at Langley Research Center. This research involved setting up the instrumentation, the lighting, the smoke, and the recording devices. The instrumentation was automated by means of a Power Macintosh running LabVIEW, a graphical instrumentation package developed by National Instruments. Routines were written to allow the tunnel conditions to be determined at a given instant at the push of a button. This included determination of tunnel pressures, speed, density, temperature, and viscosity. Other aspects of the experimental equipment included the set up of a CCD video camera with a video frame grabber, monitor, and VCR to capture the motion. A strobe light was used to highlight the smoke that was used to visualize the flow. Additional effort was put into creating a scale drawing of another tunnel on site and a limited literature search in the area of active flow control.

Corrigendum to ;Numerical dissipation control in high order shock-capturing schemes for LES of low speed flows; [J. Comput. Phys. 307 (2016) 189-202

NASA Astrophysics Data System (ADS)

Kotov, D. V.; Yee, H. C.; Wray, A. A.; Sjögreen, Björn; Kritsuk, A. G.

2018-01-01

The authors regret for the typographic errors that were made in equation (4) and missing phrase after equation (4) in the article "Numerical dissipation control in high order shock-capturing schemes for LES of low speed flows" [J. Comput. Phys. 307 (2016) 189-202].

A wind tunnel investigation of the effects of micro-vortex generators and Gurney flaps on the high-lift characteristics of a business jet wing. M.S. Thesis

NASA Technical Reports Server (NTRS)

Martuccio, Michelle Therese

1994-01-01

A study of a full-scale, semi-span business jet wing has been conducted to investigate the potential of two types of high-lift devices for improving aircraft high-lift performance. The research effort involved low-speed wind-tunnel tests of micro-vortex generators and Gurney flaps applied to the flap system of the business jet wing and included force and moment measurements, surface pressure surveys and flow visualization on the wing and flap. Results showed that the micro-vortex generators tested had no beneficial effects on the longitudinal force characteristics in this particular application, while the Gurney flaps were an effective means of increasing lift. However, the Gurney flaps also caused an increase in drag in most circumstances.

Visualization of Surface Flow on a Prolate Spheroid Model Suspended by Magnetic Suspension and Balance System

NASA Astrophysics Data System (ADS)

Ambo, Takumi; Nakamura, Yuki; Ochiai, Taku; Nonomura, Taku; Asai, Keisuke

2017-11-01

In this study, the surface flow on a 6:1 prolate spheroid model was visualized by oil flow method in the magnetic suspension and balance system (MSBS). The MSBS is a support-free system for wind-tunnel test in that a model is levitated by magnetic force. In this experiment, the 0.3-m MSBS was installed in the low-speed wind tunnel. The Reynolds number was 0.5 million and the angle of attack was set 0 and 5 degrees. In addition to free-levitation tests, a thin rod simulating disturbance of a support system was placed on the model surface and the influence of support interference was evaluated. The obtained results indicate that complicated separation patterns are present even at zero angle of attack. At α = 5°, separation pattern becomes more complicated than that at α = 0° and the streamlines form a highly three-dimensional structure. A characteristic pattern of open separation is observed and a focal point is formed at the end of the separation line. In evaluation of the support interference, the separation is delayed in the downstream of the rod, suggesting that the change of separation pattern is caused by the transition of laminar boundary layer behind the rod. These results indicate that one must take particular care to the support interference in studying three-dimensional separation on a prolate spheroid.

High-Speed Friction Stir Welding of AA7075-T6 Sheet: Microstructure, Mechanical Properties, Micro-texture, and Thermal History

NASA Astrophysics Data System (ADS)

Zhang, Jingyi; Upadhyay, Piyush; Hovanski, Yuri; Field, David P.

2018-01-01

Friction stir welding (FSW) is a cost-effective and high-quality joining process for aluminum alloys (especially heat-treatable alloys) that is historically operated at lower joining speeds (up to hundreds of millimeters per minute). In this study, we present a microstructural analysis of friction stir welded AA7075-T6 blanks with high welding speeds up to 3 M/min. Textures, microstructures, mechanical properties, and weld quality are analyzed using TEM, EBSD, metallographic imaging, and Vickers hardness. The higher welding speed results in narrower, stronger heat-affected zones (HAZs) and also higher hardness in the nugget zones. The material flow direction in the nugget zone is found to be leaning towards the welding direction as the welding speed increases. Results are coupled with welding parameters and thermal history to aid in the understanding of the complex material flow and texture gradients within the welds in an effort to optimize welding parameters for high-speed processing.

Forecasting the Short-Term Passenger Flow on High-Speed Railway with Neural Networks

PubMed Central

Xie, Mei-Quan; Li, Xia-Miao; Zhou, Wen-Liang; Fu, Yan-Bing

2014-01-01

Short-term passenger flow forecasting is an important component of transportation systems. The forecasting result can be applied to support transportation system operation and management such as operation planning and revenue management. In this paper, a divide-and-conquer method based on neural network and origin-destination (OD) matrix estimation is developed to forecast the short-term passenger flow in high-speed railway system. There are three steps in the forecasting method. Firstly, the numbers of passengers who arrive at each station or depart from each station are obtained from historical passenger flow data, which are OD matrices in this paper. Secondly, short-term passenger flow forecasting of the numbers of passengers who arrive at each station or depart from each station based on neural network is realized. At last, the OD matrices in short-term time are obtained with an OD matrix estimation method. The experimental results indicate that the proposed divide-and-conquer method performs well in forecasting the short-term passenger flow on high-speed railway. PMID:25544838

Comparisons Between NO PLIF Imaging and CFD Simulations of Mixing Flowfields for High-Speed Fuel Injectors

NASA Technical Reports Server (NTRS)

Drozda, Tomasz G.; Cabell, Karen F.; Ziltz, Austin R.; Hass, Neal E.; Inman, Jennifer A.; Burns, Ross A.; Bathel, Brett F.; Danehy, Paul M.

2017-01-01

The current work compares experimentally and computationally obtained nitric oxide (NO) planar laser induced fluorescence (PLIF) images of the mixing flowfields for three types of high-speed fuel injectors: a strut, a ramp, and a rectangular flushwall. These injection devices, which exhibited promising mixing performance at lower flight Mach numbers, are currently being studied as a part of the Enhanced Injection and Mixing Project (EIMP) at the NASA Langley Research Center. The EIMP aims to investigate scramjet fuel injection and mixing physics, and improve the understanding of underlying physical processes relevant to flight Mach numbers greater than eight. In the experiments, conducted in the NASA Langley Arc-Heated Scramjet Test Facility (AHSTF), the injectors are placed downstream of a Mach 6 facility nozzle, which simulates the high Mach number air flow at the entrance of a scramjet combustor. Helium is used as an inert substitute for hydrogen fuel. Both schlieren and PLIF techniques are applied to obtain mixing flowfield flow visualizations. The experimental PLIF is obtained by using a UV laser sheet to interrogate a plane of the flow by exciting fluorescence from the NO molecules, which are present in the AHSTF air. Consequently, the absence of signal in the resulting PLIF images is an indication of pure helium (fuel). The computational PLIF is obtained by applying a fluorescence model for NO to the results of the Reynolds-averaged simulations (RAS) of the mixing flow field carried out using the VULCAN-CFD solver. This approach is required because the PLIF signal is a nonlinear function of not only NO concentration, but also pressure, temperature, and the flow velocity. This complexity allows additional flow features to be identified and compared with those obtained from the computational fluid dynamics (CFD) simulations, however, such comparisons are only semiquantitative. Three-dimensional image reconstruction, similar to that used in magnetic resonance imaging, is also used to obtain images in the streamwise and spanwise planes from select cross-stream PLIF plane data. Synthetic schlieren is also computed from the RAS data. Good agreement between the experimental and computational results provides increased confidence in the CFD simulations for investigations of injector performance.

Comparative evaluation of three heat transfer enhancement strategies in a grooved channel

NASA Astrophysics Data System (ADS)

Herman, C.; Kang, E.

Results of a comparative evaluation of three heat transfer enhancement strategies for forced convection cooling of a parallel plate channel populated with heated blocks, representing electronic components mounted on printed circuit boards, are reported. Heat transfer in the reference geometry, the asymmetrically heated parallel plate channel, is compared with that for the basic grooved channel, and the same geometry enhanced by cylinders and vanes placed above the downstream edge of each heated block. In addition to conventional heat transfer and pressure drop measurements, holographic interferometry combined with high-speed cinematography was used to visualize the unsteady temperature fields in the self-sustained oscillatory flow. The locations of increased heat transfer within one channel periodicity depend on the enhancement technique applied, and were identified by analyzing the unsteady temperature distributions visualized by holographic interferometry. This approach allowed gaining insight into the mechanisms responsible for heat transfer enhancement. Experiments were conducted at moderate flow velocities in the laminar, transitional and turbulent flow regimes. Reynolds numbers were varied in the range Re=200-6500, corresponding to flow velocities from 0.076 to 2.36m/s. Flow oscillations were first observed between Re=1050 and 1320 for the basic grooved channel, and around Re=350 and 450 for the grooved channels equipped with cylinders and vanes, respectively. At Reynolds numbers above the onset of oscillations and in the transitional flow regime, heat transfer rates in the investigated grooved channels exceeded the performance of the reference geometry, the asymmetrically heated parallel plate channel. Heat transfer in the grooved channels enhanced with cylinders and vanes showed an increase by a factor of 1.2-1.8 and 1.5-3.5, respectively, when compared to data obtained for the basic grooved channel; however, the accompanying pressure drop penalties also increased significantly.

Low visual information-processing speed and attention are predictors of fatigue in elementary and junior high school students

PubMed Central

2011-01-01

Background Fatigue is a common complaint among elementary and junior high school students, and is known to be associated with reduced academic performance. Recently, we demonstrated that fatigue was correlated with decreased cognitive function in these students. However, no studies have identified cognitive predictors of fatigue. Therefore, we attempted to determine independent cognitive predictors of fatigue in these students. Methods We performed a prospective cohort study. One hundred and forty-two elementary and junior high school students without fatigue participated. They completed a variety of paper-and-pencil tests, including list learning and list recall tests, kana pick-out test, semantic fluency test, figure copying test, digit span forward test, and symbol digit modalities test. The participants also completed computerized cognitive tests (tasks A to E on the modified advanced trail making test). These cognitive tests were used to evaluate motor- and information-processing speed, immediate and delayed memory function, auditory and visual attention, divided and switching attention, retrieval of learned material, and spatial construction. One year after the tests, a questionnaire about fatigue (Japanese version of the Chalder Fatigue Scale) was administered to all the participants. Results After the follow-up period, we confirmed 40 cases of fatigue among 118 students. In multivariate logistic regression analyses adjusted for grades and gender, poorer performance on visual information-processing speed and attention tasks was associated with increased risk of fatigue. Conclusions Reduced visual information-processing speed and poor attention are independent predictors of fatigue in elementary and junior high school students. PMID:21672212

Low visual information-processing speed and attention are predictors of fatigue in elementary and junior high school students.

PubMed

Mizuno, Kei; Tanaka, Masaaki; Fukuda, Sanae; Yamano, Emi; Shigihara, Yoshihito; Imai-Matsumura, Kyoko; Watanabe, Yasuyoshi

2011-06-14

Fatigue is a common complaint among elementary and junior high school students, and is known to be associated with reduced academic performance. Recently, we demonstrated that fatigue was correlated with decreased cognitive function in these students. However, no studies have identified cognitive predictors of fatigue. Therefore, we attempted to determine independent cognitive predictors of fatigue in these students. We performed a prospective cohort study. One hundred and forty-two elementary and junior high school students without fatigue participated. They completed a variety of paper-and-pencil tests, including list learning and list recall tests, kana pick-out test, semantic fluency test, figure copying test, digit span forward test, and symbol digit modalities test. The participants also completed computerized cognitive tests (tasks A to E on the modified advanced trail making test). These cognitive tests were used to evaluate motor- and information-processing speed, immediate and delayed memory function, auditory and visual attention, divided and switching attention, retrieval of learned material, and spatial construction. One year after the tests, a questionnaire about fatigue (Japanese version of the Chalder Fatigue Scale) was administered to all the participants. After the follow-up period, we confirmed 40 cases of fatigue among 118 students. In multivariate logistic regression analyses adjusted for grades and gender, poorer performance on visual information-processing speed and attention tasks was associated with increased risk of fatigue. Reduced visual information-processing speed and poor attention are independent predictors of fatigue in elementary and junior high school students. © 2011 Mizuno et al; licensee BioMed Central Ltd.

Design of the low-speed NLF(1)-0414F and the high-speed HSNLF(1)-0213 airfoils with high-lift systems

NASA Technical Reports Server (NTRS)

Viken, Jeffrey K.; Watson-Viken, Sally A.; Pfenninger, Werner; Morgan, Harry L., Jr.; Campbell, Richard L.

1987-01-01

The design and testing of Natural Laminar Flow (NLF) airfoils is examined. The NLF airfoil was designed for low speed, having a low profile drag at high chord Reynolds numbers. The success of the low speed NLF airfoil sparked interest in a high speed NLF airfoil applied to a single engine business jet with an unswept wing. Work was also conducted on the two dimensional flap design. The airfoil was decambered by removing the aft loading, however, high design Mach numbers are possible by increasing the aft loading and reducing the camber overall on the airfoil. This approach would also allow for flatter acceleration regions which are more stabilizing for cross flow disturbances. Sweep could then be used to increase the design Mach number to a higher value also. There would be some degradation of high lift by decambering the airfoil overall, and this aspect would have to be considered in a final design.

Visualization of liquid-assisted hard tissue ablation with a pulsed CO2 laser

NASA Astrophysics Data System (ADS)

Li, X. W.; Chen, C. G.; Zhang, X. Z.; Zhan, Z. L.; Xie, S. S.

2015-01-01

To investigate the characteristics of liquid-mediated hard tissue ablation induced by a pulsed CO2 laser with a wavelength of 10.6 μm, a high speed camera was used to monitor the interaction between water, tissue and laser irradiation. The results showed that laser irradiation can directly impact on tissue through a vapor channel formed by the leading part of the laser pulse. The ablation debris plays a key role in liquid-assisted laser ablation, having the ability to keep the vapor channel open to extend actuation time. The runoff effect induced by vortex convection liquid flow can remove the tissue that obstructs the effect of the next laser pulse.

Unsteady motion of laser ablation plume by vortex induced by the expansion of curved shock wave

NASA Astrophysics Data System (ADS)

Tran, D. T.; Mori, K.

2017-02-01

There are a number of industrial applications of laser ablation in a gas atmosphere. When an intense pulsed laser beam is irradiated on a solid surface in the gas atmosphere, the surface material is ablated and expands into the atmosphere. At the same time, a spherical shock wave is launched by the ablation jet to induce the unsteady flow around the target surface. The ablated materials, luminously working as tracer, exhibit strange unsteady motions depending on the experimental conditions. By using a high-speed video camera (HPV-X2), unsteady motion ablated materials are visualized at the frame rate more than 106 fps, and qualitatively characterized.

Budgerigar flight in a varying environment: flight at distinct speeds?

PubMed

Schiffner, Ingo; Srinivasan, Mandyam V

2016-06-01

How do flying birds respond to changing environments? The behaviour of budgerigars, Melopsittacus undulatus, was filmed as they flew through a tapered tunnel. Unlike flying insects-which vary their speed progressively and continuously by holding constant the optic flow induced by the walls-the birds showed a tendency to fly at only two distinct, fixed speeds. They switched between a high speed in the wider section of the tunnel, and a low speed in the narrower section. The transition between the two speeds was abrupt, and anticipatory. The high speed was close to the energy-efficient, outdoor cruising speed for these birds, while the low speed was approximately half this value. This is the first observation of the existence of two distinct, preferred flight speeds in birds. A dual-speed flight strategy may be beneficial for birds that fly in varying environments, with the high speed set at an energy-efficient value for flight through open spaces, and the low speed suited to safe manoeuvring in a cluttered environment. The constancy of flight speed within each regime enables the distances of obstacles and landmarks to be directly calibrated in terms of optic flow, thus facilitating simple and efficient guidance of flight through changing environments. © 2016 The Author(s).

High-speed technique based on a parallel projection correlation procedure for digital image correlation

NASA Astrophysics Data System (ADS)

Zaripov, D. I.; Renfu, Li

2018-05-01

The implementation of high-efficiency digital image correlation methods based on a zero-normalized cross-correlation (ZNCC) procedure for high-speed, time-resolved measurements using a high-resolution digital camera is associated with big data processing and is often time consuming. In order to speed-up ZNCC computation, a high-speed technique based on a parallel projection correlation procedure is proposed. The proposed technique involves the use of interrogation window projections instead of its two-dimensional field of luminous intensity. This simplification allows acceleration of ZNCC computation up to 28.8 times compared to ZNCC calculated directly, depending on the size of interrogation window and region of interest. The results of three synthetic test cases, such as a one-dimensional uniform flow, a linear shear flow and a turbulent boundary-layer flow, are discussed in terms of accuracy. In the latter case, the proposed technique is implemented together with an iterative window-deformation technique. On the basis of the results of the present work, the proposed technique is recommended to be used for initial velocity field calculation, with further correction using more accurate techniques.

Stability and Behaviors of Methane/Propane and Hydrogen Micro Flames

NASA Astrophysics Data System (ADS)

Yoshimoto, Takamitsu; Kinoshita, Koichiro; Kitamura, Hideki; Tanigawa, Ryoichi

The flame stability limits essentially define the fundamental operation of the combustion system. Recently the micro diffusion flame has been remarked. The critical conditions of the flame stability limit are highly dependent on nozzle diameter, species of fuel and so on. The micro diffusion flame of Methane/Propane and Hydrogen is formed by using the micro-scale nozzle of which inner diameter is less than 1mm. The configurations and behaviors of the flame are observed directly and visualized by the high speed video camera The criteria of stability limits are proposed for the micro diffusion flame. The objectives of the present study are to get further understanding of lifting/blow-off for the micro diffusion flame. The results obtained are as follows. (1) The behaviors of the flames are classified into some regions for each diffusion flame. (2) The micro diffusion flame of Methane/Propane cannot be sustained, when the nozzle diameter is less than 0.14 mm. (3) The diffusion flame cannot be sustained below the critical fuel flow rate. (4) The minimum flow which is formed does not depends on the average jet velocity, but on the fuel flow rate. (5) the micro flame is laminar. The flame length is decided by fuel flow rate.

The steady-state flow quality in a model of a non-return wind tunnel

NASA Technical Reports Server (NTRS)

Mort, K. W.; Eckert, W. T.; Kelly, M. W.

1972-01-01

The structural cost of non-return wind tunnels is significantly less than that of the more conventional closed-circuit wind tunnels. However, because of the effects of external winds, the flow quality of non-return wind tunnels is an area of concern at the low test speeds required for V/STOL testing. The flow quality required at these low speeds is discussed and alternatives to the traditional manner of specifying the flow quality requirements in terms of dynamic pressure and angularity are suggested. The development of a non-return wind tunnel configuration which has good flow quality at low as well as at high test speeds is described.

Progress Toward Affordable High Fidelity Combustion Simulations Using Filtered Density Functions for Hypersonic Flows in Complex Geometries

NASA Technical Reports Server (NTRS)

Drozda, Tomasz G.; Quinlan, Jesse R.; Pisciuneri, Patrick H.; Yilmaz, S. Levent

2012-01-01

Significant progress has been made in the development of subgrid scale (SGS) closures based on a filtered density function (FDF) for large eddy simulations (LES) of turbulent reacting flows. The FDF is the counterpart of the probability density function (PDF) method, which has proven effective in Reynolds averaged simulations (RAS). However, while systematic progress is being made advancing the FDF models for relatively simple flows and lab-scale flames, the application of these methods in complex geometries and high speed, wall-bounded flows with shocks remains a challenge. The key difficulties are the significant computational cost associated with solving the FDF transport equation and numerically stiff finite rate chemistry. For LES/FDF methods to make a more significant impact in practical applications a pragmatic approach must be taken that significantly reduces the computational cost while maintaining high modeling fidelity. An example of one such ongoing effort is at the NASA Langley Research Center, where the first generation FDF models, namely the scalar filtered mass density function (SFMDF) are being implemented into VULCAN, a production-quality RAS and LES solver widely used for design of high speed propulsion flowpaths. This effort leverages internal and external collaborations to reduce the overall computational cost of high fidelity simulations in VULCAN by: implementing high order methods that allow reduction in the total number of computational cells without loss in accuracy; implementing first generation of high fidelity scalar PDF/FDF models applicable to high-speed compressible flows; coupling RAS/PDF and LES/FDF into a hybrid framework to efficiently and accurately model the effects of combustion in the vicinity of the walls; developing efficient Lagrangian particle tracking algorithms to support robust solutions of the FDF equations for high speed flows; and utilizing finite rate chemistry parametrization, such as flamelet models, to reduce the number of transported reactive species and remove numerical stiffness. This paper briefly introduces the SFMDF model (highlighting key benefits and challenges), and discusses particle tracking for flows with shocks, the hybrid coupled RAS/PDF and LES/FDF model, flamelet generated manifolds (FGM) model, and the Irregularly Portioned Lagrangian Monte Carlo Finite Difference (IPLMCFD) methodology for scalable simulation of high-speed reacting compressible flows.

The effect of virtual reality on gait variability.

PubMed

Katsavelis, Dimitrios; Mukherjee, Mukul; Decker, Leslie; Stergiou, Nicholas

2010-07-01

Optic Flow (OF) plays an important role in human locomotion and manipulation of OF characteristics can cause changes in locomotion patterns. The purpose of the study was to investigate the effect of the velocity of optic flow on the amount and structure of gait variability. Each subject underwent four conditions of treadmill walking at their self-selected pace. In three conditions the subjects walked in an endless virtual corridor, while a fourth control condition was also included. The three virtual conditions differed in the speed of the optic flow displayed as follows--same speed (OFn), faster (OFf), and slower (OFs) than that of the treadmill. Gait kinematics were tracked with an optical motion capture system. Gait variability measures of the hip, knee and ankle range of motion and stride interval were analyzed. Amount of variability was evaluated with linear measures of variability--coefficient of variation, while structure of variability i.e., its organization over time, were measured with nonlinear measures--approximate entropy and detrended fluctuation analysis. The linear measures of variability, CV, did not show significant differences between Non-VR and VR conditions while nonlinear measures of variability identified significant differences at the hip, ankle, and in stride interval. In response to manipulation of the optic flow, significant differences were observed between the three virtual conditions in the following order: OFn greater than OFf greater than OFs. Measures of structure of variability are more sensitive to changes in gait due to manipulation of visual cues, whereas measures of the amount of variability may be concealed by adaptive mechanisms. Visual cues increase the complexity of gait variability and may increase the degrees of freedom available to the subject. Further exploration of the effects of optic flow manipulation on locomotion may provide us with an effective tool for rehabilitation of subjects with sensorimotor issues.

Modeling Compressibility Effects in High-Speed Turbulent Flows

NASA Technical Reports Server (NTRS)

Sarkar, S.

2004-01-01

Man has strived to make objects fly faster, first from subsonic to supersonic and then to hypersonic speeds. Spacecraft and high-speed missiles routinely fly at hypersonic Mach numbers, M greater than 5. In defense applications, aircraft reach hypersonic speeds at high altitude and so may civilian aircraft in the future. Hypersonic flight, while presenting opportunities, has formidable challenges that have spurred vigorous research and development, mainly by NASA and the Air Force in the USA. Although NASP, the premier hypersonic concept of the eighties and early nineties, did not lead to flight demonstration, much basic research and technology development was possible. There is renewed interest in supersonic and hypersonic flight with the HyTech program of the Air Force and the Hyper-X program at NASA being examples of current thrusts in the field. At high-subsonic to supersonic speeds, fluid compressibility becomes increasingly important in the turbulent boundary layers and shear layers associated with the flow around aerospace vehicles. Changes in thermodynamic variables: density, temperature and pressure, interact strongly with the underlying vortical, turbulent flow. The ensuing changes to the flow may be qualitative such as shocks which have no incompressible counterpart, or quantitative such as the reduction of skin friction with Mach number, large heat transfer rates due to viscous heating, and the dramatic reduction of fuel/oxidant mixing at high convective Mach number. The peculiarities of compressible turbulence, so-called compressibility effects, have been reviewed by Fernholz and Finley. Predictions of aerodynamic performance in high-speed applications require accurate computational modeling of these "compressibility effects" on turbulence. During the course of the project we have made fundamental advances in modeling the pressure-strain correlation and developed a code to evaluate alternate turbulence models in the compressible shear layer.

On the measurement of turbulent fluctuations in high-speed flows using hot wires and hot films

NASA Technical Reports Server (NTRS)

Acharya, M.

1978-01-01

A hot wire has a limited life in high speed wind-tunnel flows because it is typically subjected to large dynamic loads. As a consequence hot films and modified hot wires are frequently used for turbulence measurements in such flows. However, the fluctuation sensitivities of such probes are reduced because of various factors, leading to erroneous results. This paper describes the results of tests on some sensors in both subsonic and supersonic boundary-layer flows. A simple technique to determine dynamic calibration correction factors for the sensitivities is also presented.

LES, DNS and RANS for the analysis of high-speed turbulent reacting flows

NASA Technical Reports Server (NTRS)

Adumitroaie, V.; Colucci, P. J.; Taulbee, D. B.; Givi, P.

1995-01-01

The purpose of this research is to continue our efforts in advancing the state of knowledge in large eddy simulation (LES), direct numerical simulation (DNS), and Reynolds averaged Navier Stokes (RANS) methods for the computational analysis of high-speed reacting turbulent flows. In the second phase of this work, covering the period 1 Aug. 1994 - 31 Jul. 1995, we have focused our efforts on two programs: (1) developments of explicit algebraic moment closures for statistical descriptions of compressible reacting flows and (2) development of Monte Carlo numerical methods for LES of chemically reacting flows.

Effect of high negative incidence on the performance of a centrifugal compressor stage with conventional vaned diffusers

NASA Astrophysics Data System (ADS)

Jaatinen, Ahti; Grönman, Aki; Turunen-Saaresti, Teemu; Backman, Jari

2011-06-01

Three vaned diffusers, designed to have high negative incidence (-8°) at the design operating point, are studied experimentally. The overall performance (efficiency and pressure ratio) are measured at three rotational speeds, and flow angles before and after the diffuser are measured at the design rotational speed and with three mass flow rates. The results are compared to corresponding results of the original vaneless diffuser design. Attention is paid to the performance at lower mass flows than the design mass flow. The results show that it is possible to improve the performance at mass flows lower than the design mass flow with a vaned diffuser designed with high negative incidence. However, with the vaned diffusers, the compressor still stalls at higher mass flow rates than with the vaneless one. The flow angle distributions after the diffuser are more uniform with the vaned diffusers.

Determination of Hydrodynamic Parameters on Two--Phase Flow Gas - Liquid in Pipes with Different Inclination Angles Using Image Processing Algorithm

NASA Astrophysics Data System (ADS)

Montoya, Gustavo; Valecillos, María; Romero, Carlos; Gonzáles, Dosinda

2009-11-01

In the present research a digital image processing-based automated algorithm was developed in order to determine the phase's height, hold up, and statistical distribution of the drop size in a two-phase system water-air using pipes with 0 , 10 , and 90 of inclination. Digital images were acquired with a high speed camera (up to 4500fps), using an equipment that consist of a system with three acrylic pipes with diameters of 1.905, 3.175, and 4.445 cm. Each pipe is arranged in two sections of 8 m of length. Various flow patterns were visualized for different superficial velocities of water and air. Finally, using the image processing program designed in Matlab/Simulink^, the captured images were processed to establish the parameters previously mentioned. The image processing algorithm is based in the frequency domain analysis of the source pictures, which allows to find the phase as the edge between the water and air, through a Sobel filter that extracts the high frequency components of the image. The drop size was found using the calculation of the Feret diameter. Three flow patterns were observed: Annular, ST, and ST&MI.

A Microfluidic System with Surface Patterning for Investigating Cavitation Bubble(s)-Cell Interaction and the Resultant Bioeffects at the Single-cell Level.

PubMed

Li, Fenfang; Yuan, Fang; Sankin, Georgy; Yang, Chen; Zhong, Pei

2017-01-10

In this manuscript, we first describe the fabrication protocol of a microfluidic chip, with gold dots and fibronectin-coated regions on the same glass substrate, that precisely controls the generation of tandem bubbles and individual cells patterned nearby with well-defined locations and shapes. We then demonstrate the generation of tandem bubbles by using two pulsed lasers illuminating a pair of gold dots with a few-microsecond time delay. We visualize the bubble-bubble interaction and jet formation by high-speed imaging and characterize the resultant flow field using particle image velocimetry (PIV). Finally, we present some applications of this technique for single cell analysis, including cell membrane poration with macromolecule uptake, localized membrane deformation determined by the displacements of attached integrin-binding beads, and intracellular calcium response from ratiometric imaging. Our results show that a fast and directional jetting flow is produced by the tandem bubble interaction, which can impose a highly localized shear stress on the surface of a cell grown in close proximity. Furthermore, different bioeffects can be induced by altering the strength of the jetting flow by adjusting the standoff distance from the cell to the tandem bubbles.

Increasing Navigation Speed at Endoluminal CT Colonography Reduces Colonic Visualization and Polyp Identification.

PubMed

Plumb, Andrew A; Phillips, Peter; Spence, Graeme; Mallett, Susan; Taylor, Stuart A; Halligan, Steve; Fanshawe, Thomas

2017-08-01

Purpose To investigate the effect of increasing navigation speed on the visual search and decision making during polyp identification for computed tomography (CT) colonography Materials and Methods Institutional review board permission was obtained to use deidentified CT colonography data for this prospective reader study. After obtaining informed consent from the readers, 12 CT colonography fly-through examinations that depicted eight polyps were presented at four different fixed navigation speeds to 23 radiologists. Speeds ranged from 1 cm/sec to 4.5 cm/sec. Gaze position was tracked by using an infrared eye tracker, and readers indicated that they saw a polyp by clicking a mouse. Patterns of searching and decision making by speed were investigated graphically and by multilevel modeling. Results Readers identified polyps correctly in 56 of 77 (72.7%) of viewings at the slowest speed but in only 137 of 225 (60.9%) of viewings at the fastest speed (P = .004). They also identified fewer false-positive features at faster speeds (42 of 115; 36.5%) of videos at slowest speed, 89 of 345 (25.8%) at fastest, P = .02). Gaze location was highly concentrated toward the central quarter of the screen area at faster speeds (mean gaze points at slowest speed vs fastest speed, 86% vs 97%, respectively). Conclusion Faster navigation speed at endoluminal CT colonography led to progressive restriction of visual search patterns. Greater speed also reduced both true-positive and false-positive colorectal polyp identification. © RSNA, 2017 Online supplemental material is available for this article.

Rotor redesign for a highly loaded 1800 ft/sec tip speed fan. 3: Laser Doppler velocimeter report

NASA Technical Reports Server (NTRS)

Harvey, W. B.; Hobbs, D. E.; Lee, D.; Williams, M. C.; Williams, K. F.

1982-01-01

Laser Doppler velocimeter (LDV) techniques were employed for testing a highly loaded, 550 m/sec (1800 ft/sec) tip speed, test fan stage, the objective to provide detailed mapping of the upstream, intrablade, and downstream flowfields of the rotor. Intrablade LDV measurements of velocity and flow angle were obtained along four streamlines passing through the leading edge at 45%, 69%, 85%, and 95% span measured from hub to tip, at 100% of design speed, peak efficiency; 100% speed, near surge; and 95% speed, peak efficiency. At the design point, most passages appeared to have a strong leading edge shock, which moved forward with increasing strength near surge and at part speeds. The flow behind the shock was of a complex mixed subsonic and supersonic form. The intrablade flowfields were found to be significantly nonperiodic at 100% design speed, peak efficiency.