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1

Effect of a novel temperature-controlled laminar airflow device on personal breathing zone aeroallergen exposure.  

PubMed

Temperature-controlled laminar airflow improves symptoms in atopic asthmatics, but its effects on personal allergen exposure are unknown. We aimed to evaluate its effects on personal cat allergen and particulate exposures in a simulated bedroom environment. Five healthy volunteers lay under an active and an inactive temperature-controlled laminar airflow device for 175 min, in a simulated bedroom containing bedding from a cat owner. Total airborne particles (?0.5 - ?10 ?m diameter) were quantified with a laser particle counter. Airborne allergen was sampled with Institute of Occupational Medicine filters. Inhaled exposure was sampled with nasal air samplers. Allergen-containing particles were quantified by immunoassay. Treatment reduced total airborne particles (>0.5 ?m diameter) by >99% (P < 0.001) and reduced airborne allergen concentration within the breathing zone (ratio of median counts = 30, P = 0.043). Treatment reduced inhaled allergen (ratio of median counts = 7, P = 0.043). Treatment was not associated with a change in airborne allergen concentration outside of the breathing zone (P = 0.160). Temperature-controlled laminar airflow treatment of individuals in an allergen-rich experimental environment results in significant reductions in breathing zone allergenic and non-allergenic particle exposure, and in inhaled cat allergen exposure. These findings may explain the clinical benefits of temperature-controlled laminar airflow. PMID:24750266

Gore, R B; Boyle, R J; Gore, C; Custovic, A; Hanna, H; Svensson, P; Warner, J O

2015-02-01

2

Surgical clothing systems in laminar airflow operating room: a numerical assessment.  

PubMed

This study compared two different laminar airflow distribution strategies - horizontal and vertical - and investigated the effectiveness of both ventilation systems in terms of reducing the sedimentation and distribution of bacteria-carrying particles. Three different staff clothing systems, which resulted in source strengths of 1.5, 4 and 5CFU/s per person, were considered. The exploration was conducted numerically using a computational fluid dynamics technique. Active and passive air sampling methods were simulated in addition to recovery tests, and the results were compared. Model validation was performed through comparisons with measurement data from the published literature. The recovery test yielded a value of 8.1min for the horizontal ventilation scenario and 11.9min for the vertical ventilation system. Fewer particles were captured by the slit sampler and in sedimentation areas with the horizontal ventilation system. The simulated results revealed that under identical conditions in the examined operating room, the horizontal laminar ventilation system performed better than the vertical option. The internal constellation of lamps, the surgical team and objects could have a serious effect on the movement of infectious particles and therefore on postoperative surgical site infections. PMID:25155072

Sadrizadeh, Sasan; Holmberg, Sture

2014-01-01

3

Microbiological Studies on the Performance of a Laminar Airflow Biological Cabinet  

PubMed Central

Engineering and microbiological tests indicated that a typical, commercial laminar airflow cabinet was not effective in providing either product protection or agent containment. The cabinet was modified and tested through a series of alternate configurations to establish a set of design criteria. A mock-up cabinet was developed from these design criteria. The mock-up unit was evaluated for efficiency in providing both product protection and agent containment. In these evaluations, challenge methods were developed to simulate normal, in-use laboratory operations. Controlled bacterial or viral aerosol challenges were used at higher than normal levels to provide stringent test conditions. Test results indicated that the mock-up unit was considerably better in preventing agent penetration (0.1 to 0.2 particles per 100 ft3 of air) than the commercial cabinet (5 to 6 particles per 100 ft3 of air) during product protection tests. Similarly, agent containment was considerably better in the new cabinet (particle escape of 2 to 3 per 100 ft3 of air at only one of the five test sites) than in the commercial cabinet (particle escape of 2 to 14 per 100 ft3 of air at three of the five test sites). PMID:4874462

Mcdade, Joseph J.; Sabel, Fred L.; Akers, Ronald L.; Walker, Robert J.

1968-01-01

4

Airflow Research  

NASA Technical Reports Server (NTRS)

This is an overview of research being done in laminar flow at Ames Dryden Flight Research Center and Langley Research Center. Airflow research at Ames Dryden has resulted in a special wing covering that will artificially induce laminar flow on the wing surface; this specially adapted wing is shown being tested in different flying conditions. This video also features research done at Langley in producing a chemical covering for wings that will make visible natural laminar flow and turbulent airflow patterns as they occur. Langley researchers explain possible use of this technology in supersonic flight.

1985-01-01

5

Timeline Analysis Program (TLA-1)  

NASA Technical Reports Server (NTRS)

The Timeline Analysis Program (TLA-1) was described. This program is a crew workload analysis computer program that was developed and expanded from previous workload analysis programs, and is designed to be used on the NASA terminal controlled vehicle program. The following information is described: derivation of the input data, processing of the data, and form of the output data. Eight scenarios that were created, programmed, and analyzed as verification of this model were also described.

Miller, K. H.

1976-01-01

6

Radiation Characteristics of Chlamydomonas reinhardtii CC125 and Its Truncated Chlorophyll Antenna Transformants tla1, tlaX, and 37RP1-tla1  

E-print Network

concentration of each di- lution was determined using calibration curves that relate the optical density (optical density (OD) at 750 nm for all strains. Table 2: Chlorophyll (Chl) concentrationsConcentration (kg cell/m3) CC125 tla1 tlaX tla1-CW+ 0.3665x X y = = 0.367 OD R 2 = 0.997 Optical Density

Berberoglu, Halil; Pilon, Laurent; Melis, Anastasios

2008-01-01

7

Timeline analysis program (TLA-1), appendices  

NASA Technical Reports Server (NTRS)

Appendices for the Timeline Analysis Program (TLA-1) were given. The appendices contain the Atlanta terminal area scenarios, the task catalog and the control and display configurations for the forward and aft flight decks of the NASA 515 aircraft, and the event/procedure, phase, mission, and subsystem catalogs.

Miller, K. H.

1976-01-01

8

Mechanical Verification of Concurrent Systems with TLA  

Microsoft Academic Search

Abstract. We describe an initial version of a system for mechanically checking the correctness proof of a concurrent system.Input to the system consists of the correctness properties, expressed in TLA (the temporal logic of actions), and their proofs, written in a humanly readable, hierarchically structured form.The system uses a mechanical verifier to check each step of the proof, translating the

Urban Engberg; Peter Grønning; Leslie Lamport

1992-01-01

9

Steam boiler control specification problem: A TLA solution  

E-print Network

Steam boiler control specification problem: A TLA solution Frank Le�ke and Stephan Merz Institut f of the state of the steam boiler, detect failures, and model message transmission. We give a more detailed between the physi­ cal state of the steam boiler and the model maintained by the controller and discuss

Merz, Stephan

10

Steam boiler control speci cation problem: A TLA solution  

E-print Network

Steam boiler control speci cation problem: A TLA solution Frank Le ke and Stephan Merz Institut fur of the state of the steam boiler, detect failures, and model message transmission. We give a more detailed between the physi- cal state of the steam boiler and the model maintained by the controller and discuss

11

F-16XL Supersonic Laminar Flow Test Flight - Duration: 0:29.  

NASA Video Gallery

An F-16XL aircraft was used by the Dryden Flight Research Center, Edwards, California, in a NASA-wide program to improve laminar airflow on aircraft flying at sustained supersonic speeds. It was th...

12

Assessing multizone airflow software  

SciTech Connect

Multizone models form the basis of most computer simulations of airflow and pollutant transport in buildings. In order to promote computational efficiency, some multizone simulation programs, such as COMIS and CONTAM, restrict the form that their flow models may take. While these tools allow scientists and engineers to explore a wide range of building airflow problems, increasingly their use has led to new questions not answerable by the current generation of programs. This paper, directed at software developers working on the next generation of building airflow models, identifies structural aspects of COMIS and related programs that prevent them from easily incorporating desirable new airflow models. The paper also suggests criteria for evaluating alternate simulation environments for future modeling efforts.

Lorenzetti, D.M.

2001-12-01

13

Natural laminar flow and laminar flow control  

NASA Technical Reports Server (NTRS)

The present volume discusses the development history and basic concepts of laminar flow control, laminar flow flight experiments, subsonic laminar-flow airfoils, and a design philosophy for long-range laminar flow-control commercial transports with advanced supercritical airfoils. Also discussed are the relationship of wave-interaction theory to laminar flow control, supersonic laminar flow control, and the NASA-Langley 8-ft Transonic Pressure Tunnel.

Barnwell, R. W. (editor); Hussaini, M. Y. (editor)

1992-01-01

14

Structure of laminar sooting inverse diffusion flames  

Microsoft Academic Search

The flame structure of laminar inverse diffusion flames (IDFs) was studied to gain insight into soot formation and growth in underventilated combustion. Both ethylene–air and methane–air IDFs were examined, fuel flow rates were kept constant for all flames of each fuel type, and airflow rates were varied to observe the effect on flame structure and soot formation. Planar laser-induced fluorescence

Mark A. Mikofski; Timothy C. Williams; Christopher R. Shaddix; A. Carlos Fernandez-Pello; Linda G. Blevins

2007-01-01

15

Structure of laminar sooting inverse diffusion flames  

Microsoft Academic Search

The flame structure of laminar inverse diffusion flames (IDFs) was studied to gain insight into soot formation and growth in underventilated combustion. Both ethylene-air and methane-air IDFs were examined, fuel flow rates were kept constant for all flames of each fuel type, and airflow rates were varied to observe the effect on flame structure and soot formation. Planar laser-induced fluorescence

Mark A. Mikofski; A. Carlos Fernandez-Pello; Timothy C. Williams; Christopher R. Shaddix; Linda G. Blevins

2007-01-01

16

Embryonal Carcinoma Cells Express Qa and Tla Class I Genes of the Major Histocompatibility Complex  

Microsoft Academic Search

The murine major histocompatibility complex encodes H-2K and H-2D transplantation antigens and other class I-like proteins called Qa and Tla molecules; the functions of the Qa\\/Tla molecules are not known. That they may participate in embryonic cell--cell interactions and\\/or play a role in immune responses against tumors has been speculated. We have studied two murine embryonal carcinoma tumors, 402AX and

Suzanne Ostrand-Rosenberg; Deborah A. Nickerson; Virginia K. Clements; Elizabeth P. Garcia; Esi Lamouse-Smith; Leroy Hood; Iwona Stroynowski

1989-01-01

17

Laminar Flow Aircraft Certification  

NASA Technical Reports Server (NTRS)

Various topics telative to laminar flow aircraft certification are discussed. Boundary layer stability, flaps for laminar flow airfoils, computational wing design studies, manufacturing requirements, windtunnel tests, and flow visualization are among the topics covered.

Williams, Louis J. (compiler)

1986-01-01

18

Effect of sewer headspace air-flow on hydrogen sulfide removal by corroding concrete surfaces.  

PubMed

Hydrogen sulfide adsorption and oxidation by corroding concrete surfaces at different air-flows were quantified using a pilot-scale sewer reactor. The setup was installed in an underground sewer research station with direct access to wastewater. Hydrogen sulfide gas was injected into the headspace of the sewer reactor once per hour in peak concentrations of approximately 500 ppmv. The investigated range of sewer air-flows was representative for natural ventilated sewer systems, and covered both laminar and turbulent conditions. The experiments demonstrated a significant effect of sewer air-flow on the kinetics of hydrogen sulfide removal from the sewer headspace. From the lowest to the highest air-flow investigated, the rate of adsorption and oxidation increased more than threefold. At all air-flows, the reaction kinetics followed a simple n-th order rate equation with a reaction order of 0.8. The effect of air-flow on hydrogen sulfide adsorption and oxidation kinetics was quantified by a simple empirical equation. PMID:22755494

Nielsen, Asbjørn Haaning; Hvitved-Jacobsen, Thorkild; Vollertsen, Jes

2012-03-01

19

MICROPROCESSOR CONTROL OF ROTOGRAVURE AIRFLOWS  

EPA Science Inventory

The report discusses the technical and economic viability of using micro-processor-based control technology to collect volatile organic compound (VOC) emissions from a paper coating operation. The microprocessor-based control system monitors and controls both the airflow rate and...

20

Aircraft Laminar Flow Control  

NASA Technical Reports Server (NTRS)

Aircraft laminar flow control (LFC) from the 1930's through the 1990's is reviewed and the current status of the technology is assessed. Examples are provided to demonstrate the benefits of LFC for subsonic and supersonic aircraft. Early studies related to the laminar boundary-layer flow physics, manufacturing tolerances for laminar flow, and insect-contamination avoidance are discussed. LFC concept studies in wind-tunnel and flight experiments are the major focus of the paper. LFC design tools are briefly outlined for completeness.

Joslin, Ronald D.

1998-01-01

21

Power requirement of rotating rods in airflow  

NASA Technical Reports Server (NTRS)

Experiments were performed to determine the power required for rotating a rotor disc fitted with a number of radially arranged rods placed into a ducted airflow. An array of stationary rods, also radially arranged, were placed upstream close to the rotor with a small gap between the rods to cause wake interference. The results show that power increased with increasing airflow and the rate of increase varied considerably. At lower values of airflow the rate of increase was larger than at higher airflow and definite power peaks occurred at certain airflow rates, where the power attained a maximum within the test airflow range. During the test a maximum blade passage frequency of 2037 Hz was attained.

Barna, P. S.; Crossman, G. R.

1974-01-01

22

Torque requirement of rotating rods in airflow  

NASA Technical Reports Server (NTRS)

Experiments were performed to determine the torque required for rotating a rotor disk fitted with a number of radially arranged rods placed into a ducted airflow. An array of stationary rods, also radially arranged, was placed upstream close to the rotor with a small gap between the rods to cause wake interference. The results show that torque generally increased with airflow and the rate of increase varied considerably. At lower values of airflow, the rate of increase was larger than at higher airflow, and definite torque peaks occurred at certain airflow rates, where the torque attained a maximum within the test airflow range. During the test, a maximum blade passage frequency of 2037 Hz was attained. The results also show that the torque peaks occurred at the same Strouhal number for all speeds.

Barna, P. S.; Crossman, G. R.

1979-01-01

23

Laminar Soot Processes  

NASA Technical Reports Server (NTRS)

Soot formation within hydrocarbon-fueled flames is an important unresolved problem of combustion science for several reasons: soot emissions are responsible for more deaths than any other combustion pollutant, thermal loads due to continuum radiation from soot limit the durability of combustors, thermal radiation from soot is mainly responsible for the growth and spread of unwanted fires, carbon monoxide associated with soot emissions is responsible for most fire deaths, and limited understanding of soot processes is a major impediment to the development of computational combustion. Thus, soot processes within laminar nonpremixed (diffusion) flames are being studied, emphasizing space-based experiments at microgravity. The study is limited to laminar flames due to their experimental and computational tractability, noting the relevance of these results to practical flames through laminar flamelet concepts. The microgravity environment is emphasized because buoyancy affects soot processes in laminar diffusion flames whereas effects of buoyancy are small for most practical flames. Results discussed here were obtained from experiments carried out on two flights of the Space Shuttle Columbia. After a brief discussion of experimental methods, results found thus far are described, including soot concentration measurements, laminar flame shapes, laminar smoke points and flame structure. The present discussion is brief.

Lin, K. -C.; Dai, Z.; Faeth, G. M.

1999-01-01

24

Development of laminar flow control wing surface porous structure  

NASA Technical Reports Server (NTRS)

It was concluded that the chordwise air collection method, which actually combines chordwise and spanwise air collection, is the best of the designs conceived up to this time for full chord laminar flow control (LFC). Its shallower ducting improved structural efficiency of the main wing box resulting in a reduction in wing weight, and it provided continuous support of the chordwise panel joints, better matching of suction and clearing airflow requirements, and simplified duct to suction source minifolding. Laminar flow control on both the upper and lower surfaces was previously reduced to LFC suction on the upper surface only, back to 85 percent chord. The study concludes that, in addition to reduced wing area and other practical advantages, this system would be lighter because of the increase in effective structural wing thickness.

Klotzsche, M.; Pearce, W.; Anderson, C.; Thelander, J.; Boronow, W.; Gallimore, F.; Brown, W.; Matsuo, T.; Christensen, J.; Primavera, G.

1984-01-01

25

Measuring Residential Ventilation System Airflows: Part 2 -Field  

E-print Network

1 Measuring Residential Ventilation System Airflows: Part 2 - Field Evaluation of Airflow Meter Residential Ventilation System Airflows: Part 2 - Field Evaluation of Airflow Meter Devices and System Flow, mechanical ventilation, measurement, ASHRAE 62.2, flow hood ABSTRACT The 2008 California State Energy Code

26

Supersonic laminar flow control research  

NASA Technical Reports Server (NTRS)

The objective of the research is to understand supersonic laminar flow stability, transition, and active control. Some prediction techniques will be developed or modified to analyze laminar flow stability. The effects of supersonic laminar flow with distributed heating and cooling on active control will be studied. The primary tasks of the research applying to the NASA/Ames Proof of Concept (POC) Supersonic Wind Tunnel and Laminar Flow Supersonic Wind Tunnel (LFSWT) nozzle design with laminar flow control are as follows: (1) predictions of supersonic laminar boundary layer stability and transition, (2) effects of wall heating and cooling for supersonic laminar flow control, and (3) performance evaluation of POC and LFSWT nozzles design with wall heating and cooling effects applying at different locations and various length.

Lo, Ching F.

1994-01-01

27

Development of Power-head based Fan Airflow Station  

E-print Network

without any branches, the airflow is measured based on the pressure drop through the main duct and then the stack damper is controlled by the measured airflow. During the measurement the airflow was obtained by the measured duct pressure drop...Development of Power-head Based Fan Airflow Station Gang Wang Research associate University of Nebraska, Lincoln Mingsheng Liu Professor University of Nebraska, Lincoln Abstract Fan airflow measurement is critical for heating...

Wang, G.; Liu, M.

2005-01-01

28

Airflow resistance of selected biomass materials  

SciTech Connect

Pressure drop created when air was forced through beds of selected biomass materials was determined. Materials tested included peanut hulls, peanut hull pellets, maize cobs, and wood shavings, chips and bark. The data were presented as logarithmic plots and equations of pressure drop versus airflow. The airflow resistances of the biomass materials increased with an increase in bulk density and were found to be in the range between values for ear and shelled maize. 12 references.

Cooper, S.C.; Sumner, H.R.

1985-01-01

29

Laminar Soot Processes (LSP)  

NASA Technical Reports Server (NTRS)

This is the final report of a research program considering the structure and the soot surface reaction properties of laminar nonpremixed (diffusion) flames. The study was limited to ground-based measurements of buoyant laminar jet diffusion flames at pressures of 0.1-1.0 atm. The motivation for the research is that soot formation in flames is a major unresolved problem of combustion science that influences the pollutant emissions, durability and performance of power and propulsion systems, as well as the potential for developing computational combustion. The investigation was divided into two phases considering the structure of laminar soot-containing diffusion flames and the soot surface reaction properties (soot surface growth and oxidation) of these flames, in turn. The first phase of the research addressed flame and soot structure properties of buoyant laminar jet diffusion flames at various pressures. The measurements showed that H, OH and O radical concentrations were generally in superequilibrium concentrations at atmospheric pressure but tended toward subequilibrium concentrations as pressures decreased. The measurements indicated that the original fuel decomposed into more robust compounds at elevated temperatures, such as acetylene (unless the original fuel was acetylene) and H, which are the major reactants for soot surface growth, and that the main effect of the parent fuel on soot surface growth involved its yield of acetylene and H for present test conditions. The second phase of the research addressed soot surface reaction properties, e.g., soot surface growth and surface oxidation. It was found that soot surface growth rates in both laminar premixed and diffusion flames were in good agreement, that these rates were relatively independent of fuel type, and that these rates could be correlated by the Hydrogen-Abstraction/Carbon-Addition (HACA) mechanisms of Colket and Hall (1994), Frenklach et al. (1990,1994), and Kazakov et al. (1995). It was also found that soot surface oxidation rates were relatively independent of fuel type, were not correlated with O2, CO2, H2O and O collision rates but were correlated with the collision rates of OH with a collision efficiency of 0.14, in agreement with the early measurements in premixed flames of Neoh et al. (1980), after allowing for oxidation by O2 via the classical rate expression of Nagle and Strickland-Constable (1962).

Dai, Z.; El-Leathy, A. M.; Kim, C. H.; Krishnan, S. S.; Lin, K.-C.; Xu, F.; Faeth, G. M.

2002-01-01

30

Structure of laminar sooting inverse diffusion flames  

SciTech Connect

The flame structure of laminar inverse diffusion flames (IDFs) was studied to gain insight into soot formation and growth in underventilated combustion. Both ethylene-air and methane-air IDFs were examined, fuel flow rates were kept constant for all flames of each fuel type, and airflow rates were varied to observe the effect on flame structure and soot formation. Planar laser-induced fluorescence of hydroxyl radicals (OH PLIF) and polycyclic aromatic hydrocarbons (PAH PLIF), planar laser-induced incandescence of soot (soot PLII), and thermocouple-determined gas temperatures were used to draw conclusions about flame structure and soot formation. Flickering, caused by buoyancy-induced vortices, was evident above and outside the flames. The distances between the OH, PAH, and soot zones were similar in IDFs and normal diffusion flames (NDFs), but the locations of those zones were inverted in IDFs relative to NDFs. Peak OH PLIF coincided with peak temperature and marked the flame front. Soot appeared outside the flame front, corresponding to temperatures around the minimum soot formation temperature of 1300 K. PAHs appeared outside the soot layer, with characteristic temperature depending on the wavelength detection band. PAHs and soot began to appear at a constant axial position for each fuel, independent of the rate of air flow. PAH formation either preceded or coincided with soot formation, indicating that PAHs are important components in soot formation. Soot growth continued for some time downstream of the flame, at temperatures below the inception temperature, probably through reaction with PAHs. (author)

Mikofski, Mark A.; Fernandez-Pello, A. Carlos [Microgravity Combustion Laboratory, University of California Berkeley, Berkeley, CA 94720 (United States); Williams, Timothy C.; Shaddix, Christopher R.; Blevins, Linda G. [Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94550 (United States)

2007-06-15

31

Measurement of airflow in residential furnaces  

SciTech Connect

In order to have a standard for furnaces that includes electricity consumption or for the efficiency of furnace blowers to be determined, it is necessary to determine the airflow of a furnace or furnace blower. This study focused on airflow testing, in order to determine if an existing test method for measuring blower airflow could be used to measure the airflow of a furnace, under conditions seen in actual installations and to collect data and insights into the operating characteristics of various types of furnace blowers, to use in the analysis of the electricity consumption of furnaces. Results of the measured airflow on furnaces with three types of blower and motor combinations are presented in the report. These included: (1) a forward-curved blower wheel with a typical permanent split capacitor (PSC) motor, (2) a forward-curved blower wheel with an electronically-commutated motor (ECM), and (3) a prototype blower, consisting of a backward-inclined blower wheel matched to an ECM motor prototype, which is being developed as an energy-saving alternative to conventional furnace blowers. The testing provided data on power consumption, static and total pressure, and blower speed.

Biermayer, Peter J.; Lutz, James; Lekov, Alex

2004-01-24

32

Optimal Airflow Control for Laboratory Air Handling Unit (LAHU) Systems  

E-print Network

An optimal airflow control method and procedure have been developed for laboratory air handing unit (LAHU) systems using linear optimization theories. The optimal airflow control minimizes the thermal energy consumption and the cost, and improves...

Cui, Y.; Liu, M.; Conger, K.

2002-01-01

33

AIRFLOW CHARACTERISTICS IN A BABOON NASAL PASSAGE CAST  

EPA Science Inventory

Airflow patterns in the nasal Passages influence the distribution of air-pollutant-induced lesions in the airway mucosa. ittle is known about airflow characteristics or the complex nasopharyngeal airway of man and experimental animals. irflow characteristics in the nasopharyngeal...

34

A Prototype Flight-Deck Airflow Hazard Visualization System  

NASA Technical Reports Server (NTRS)

Airflow hazards such as turbulence, vortices, or low-level wind shear can pose a threat to landing aircraft and are especially dangerous to helicopters. Because pilots usually cannot see airflow, they may be unaware of the extent of the hazard. We have developed a prototype airflow hazard visual display for use in helicopter cockpits to alleviate this problem. We report on the results of a preliminary usability study of our airflow hazard visualization system in helicopter-shipboard operations.

Aragon, Cecilia R.

2004-01-01

35

On wind turbine power performance measurements at inclined airflow  

Microsoft Academic Search

The average airflow inclination in complex terrain may be substantial. The airflow inclination affects wind turbine performance and also affects the cup anemometer being used in power performance measurements. In this article the overall dependence of the power curve on inclined airflow is analysed for its influence on both the wind turbine and the cup anemometer. The wind turbine performance

T. F. Pedersen

2004-01-01

36

Continuous laminar smoke generator  

NASA Technical Reports Server (NTRS)

A smoke generator capable of emitting a very thin, laminar stream of smoke for use in high detail flow visualization was invented. The generator is capable of emitting a larger but less stable rope of smoke. The invention consists of a pressure supply and fluid supply which supply smoke generating fluid to feed. The feed tube is directly heated by electrical resistance from current supplied by power supply and regulated by a constant temperature controller. A smoke exit hole is drilled in the wall of feed tube. Because feed tube is heated both before and past exit hole, no condensation of smoke generating occurs at the smoke exit hole, enabling the production of a very stable smoke filament. The generator is small in size which avoids wind turbulence in front of the test model.

Weinstein, L. M. (inventor)

1985-01-01

37

The natural history of chronic airflow obstruction  

Microsoft Academic Search

A prospective epidemiological study of the early stages of the development of chronic obstructive pulmonary disease was performed on London working men. The findings showed that forced expiratory volume in one second (FEV1) falls gradually over a lifetime, but in most non-smokers and many smokers clinically significant airflow obstruction never develops. In susceptible people, however, smoking causes irreversible obstructive changes.

C Fletcher; R Peto

1977-01-01

38

Overview of Laminar Flow Control  

NASA Technical Reports Server (NTRS)

The history of Laminar Flow Control (LFC) from the 1930s through the 1990s is reviewed and the current status of the technology is assessed. Early studies related to the natural laminar boundary-layer flow physics, manufacturing tolerances for laminar flow, and insect-contamination avoidance are discussed. Although most of this publication is about slot-, porous-, and perforated-suction LFC concept studies in wind tunnel and flight experiments, some mention is made of thermal LFC. Theoretical and computational tools to describe the LFC aerodynamics are included for completeness.

Joslin, Ronald D.

1998-01-01

39

Truncated photosystem chlorophyll antenna size in the green microalga Chlamydomonas reinhardtii upon deletion of the TLA3-CpSRP43 gene.  

PubMed

The truncated light-harvesting antenna size3 (tla3) DNA insertional transformant of Chlamydomonas reinhardtii is a chlorophyll-deficient mutant with a lighter green phenotype, a lower chlorophyll (Chl) per cell content, and higher Chl a/b ratio than corresponding wild-type strains. Functional analyses revealed a higher intensity for the saturation of photosynthesis and greater light-saturated photosynthetic activity in the tla3 mutant than in the wild type and a Chl antenna size of the photosystems that was only about 40% of that in the wild type. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis and western-blot analyses showed that the tla3 strain was deficient in the Chl a/b light-harvesting complex. Molecular and genetic analyses revealed a single plasmid insertion in chromosome 4 of the tla3 nuclear genome, causing deletion of predicted gene g5047 and plasmid insertion within the fourth intron of downstream-predicted gene g5046. Complementation studies defined that gene g5047 alone was necessary and sufficient to rescue the tla3 mutation. Gene g5047 encodes a C. reinhardtii homolog of the chloroplast-localized SRP43 signal recognition particle, whose occurrence and function in green microalgae has not hitherto been investigated. Biochemical analysis showed that the nucleus-encoded and chloroplast-localized CrCpSRP43 protein specifically operates in the assembly of the peripheral components of the Chl a/b light-harvesting antenna. This work demonstrates that cpsrp43 deletion in green microalgae can be employed to generate tla mutants with a substantially diminished Chl antenna size. The latter exhibit improved solar energy conversion efficiency and photosynthetic productivity under mass culture and bright sunlight conditions. PMID:23043081

Kirst, Henning; Garcia-Cerdan, Jose Gines; Zurbriggen, Andreas; Ruehle, Thilo; Melis, Anastasios

2012-12-01

40

Hybrid Mesh for Nasal Airflow Studies  

PubMed Central

The accuracy of the numerical result is closely related to mesh density as well as its distribution. Mesh plays a very significant role in the outcome of numerical simulation. Many nasal airflow studies have employed unstructured mesh and more recently hybrid mesh scheme has been utilized considering the complexity of anatomical architecture. The objective of this study is to compare the results of hybrid mesh with unstructured mesh and study its effect on the flow parameters inside the nasal cavity. A three-dimensional nasal cavity model is reconstructed based on computed tomographic images of a healthy Malaysian adult nose. Navier-Stokes equation for steady airflow is solved numerically to examine inspiratory nasal flow. The pressure drop obtained using the unstructured computational grid is about 22.6?Pa for a flow rate of 20?L/min, whereas the hybrid mesh resulted in 17.8?Pa for the same flow rate. The maximum velocity obtained at the nasal valve using unstructured grid is 4.18?m/s and that with hybrid mesh is around 4.76?m/s. Hybrid mesh reported lower grid convergence index (GCI) than the unstructured mesh. Significant differences between unstructured mesh and hybrid mesh are determined highlighting the usefulness of hybrid mesh for nasal airflow studies. PMID:23983811

Zubair, Mohammed; Abdullah, Mohammed Zulkifly; Ahmad, Kamarul Arifin

2013-01-01

41

Hybrid mesh for nasal airflow studies.  

PubMed

The accuracy of the numerical result is closely related to mesh density as well as its distribution. Mesh plays a very significant role in the outcome of numerical simulation. Many nasal airflow studies have employed unstructured mesh and more recently hybrid mesh scheme has been utilized considering the complexity of anatomical architecture. The objective of this study is to compare the results of hybrid mesh with unstructured mesh and study its effect on the flow parameters inside the nasal cavity. A three-dimensional nasal cavity model is reconstructed based on computed tomographic images of a healthy Malaysian adult nose. Navier-Stokes equation for steady airflow is solved numerically to examine inspiratory nasal flow. The pressure drop obtained using the unstructured computational grid is about 22.6?Pa for a flow rate of 20?L/min, whereas the hybrid mesh resulted in 17.8?Pa for the same flow rate. The maximum velocity obtained at the nasal valve using unstructured grid is 4.18?m/s and that with hybrid mesh is around 4.76?m/s. Hybrid mesh reported lower grid convergence index (GCI) than the unstructured mesh. Significant differences between unstructured mesh and hybrid mesh are determined highlighting the usefulness of hybrid mesh for nasal airflow studies. PMID:23983811

Zubair, Mohammed; Abdullah, Mohammed Zulkifly; Ahmad, Kamarul Arifin

2013-01-01

42

The association between airflow obstruction and radiologic change by tuberculosis  

PubMed Central

Introduction Cigarette smoking is the most commonly encountered risk factor for chronic obstructive pulmonary disease (COPD). However, it is not the only one and there is consistent evidence from epidemiologic studies that nonsmokers may develop chronic airflow limitation. A history of tuberculosis has recently been found to be associated with airflow obstruction in adults older than 40 years. The aim of this study was to evaluate the association between the radiologic changes by tuberculosis and airflow obstruction in a population based sample. Methods A nationwide COPD prevalence survey was conducted. We compared the prevalence of airflow obstruction according to the presence of the radiologic change by the tuberculosis. Results We analyzed 1,384 subjects who participated in the nationwide Korean COPD survey. All subjects were older than 40 years and took the spirometry and simple chest radiography. We defined the airflow obstruction as FEV1/FVC <0.7. A total of 149 (10.8%) subjects showed airflow obstruction. A total of 167 (12.1%) subjects showed radiologic change by tuberculosis. Among these 167 subjects, 44 (26.3%) had airflow obstruction. For the subjects without radiologic change by tuberculosis, the prevalence of airflow obstruction was only 8.6%. The unadjusted odds ratio for airflow obstruction according to the radiologic change was 3.788 (95% CI: 2.544-5.642). Conclusions The radiologic change by tuberculosis was associated with airflow obstruction. PMID:24822105

Hwang, Yong Il; Kim, Joo Hee; Lee, Chang Youl; Park, Sunghoon; Park, Yong Bum; Jang, Seung Hun; Kim, Cheol Hong; Shin, Tae Rim; Park, Sang Myun; Sim, Yun Su; Kim, Dong-Gyu; Lee, Myung-Goo; Hyun, In-Gyu

2014-01-01

43

Effects of the ambient temperature on the airflow across a Caucasian nasal cavity.  

PubMed

We analyse the effects of the air ambient temperature on the airflow across a Caucasian nasal cavity under different ambient temperatures using CFD simulations. A three-dimensional nasal model was constructed from high-resolution computed tomography images for a nasal cavity from a Caucasian male adult. An exhaustive parametric study was performed to analyse the laminar-compressible flow driven by two different pressure drops between the nostrils and the nasopharynx, which induced calm breathing flow rates???5.7?L/min and???11.3?L/min. The inlet air temperature covered the range?-?10(o) C ? To ?50(o) C. We observed that, keeping constant the wall temperature of the nasal cavity at 37(o) C, the ambient temperature affects mainly the airflow velocity into the valve region. Surprisingly, we found an excellent linear relationship between the ambient temperature and the air average temperature reached at different cross sections, independently of the pressure drop applied. Finally, we have also observed that the spatial evolution of the mean temperature data along the nasal cavity can be collapsed for all ambient temperatures analysed with the introduction of suitable dimensionless variables, and this evolution can be modelled with the help of hyperbolic functions, which are based on the heat exchanger theory. PMID:24574201

Burgos, M A; Sanmiguel-Rojas, E; Martín-Alcántara, A; Hidalgo-Martínez, M

2014-03-01

44

Laminar flow control is maturing  

NASA Technical Reports Server (NTRS)

Recent research demonstrates that laminar flow (LF) can be reliable in flight and that the support system need not be complex. Shaping produces favorable pressure gradients for maintaining natural laminar flow (NLF), and laminar flow control (LFC) techniques such as full chord suction promise a fuel-saving payoff of up to 30 percent on long-range missions. For large aircraft, current research is concentrated on hybrid LFC concepts which combine suction and pressure-gradient control. At NASA Ames, an F-14 with variable wing sweep has been flight tested with smooth surface gloves on the wings; preliminary results indicate high transition Reynolds numbers to sweep angles as large as 25 deg. In addition, a 757 was flight tested with an NLF glove on the right wing just outboard of the engine pylon; and the LF was found to be suprisingly robust.

Wagner, Richard D.; Bartlett, Dennis W.; Maddalon, Dal V.

1988-01-01

45

Considerations for efficient airflow design in cleanrooms  

SciTech Connect

A high-performance cleanroom should provide efficient energy performance in addition to effective contamination control. Energy-efficient designs can yield capital and operational cost savings, and can be part of a strategy to improve productivity in the cleanroom industry. Based upon in-situ measurement data from ISO Class 5 clean rooms, this article discusses key factors affecting cleanroom air system performance and benefits of efficient airflow design in clean rooms. Cleanroom HVAC systems used in the semiconductor, pharmaceutical, and healthcare industries are very energy intensive, requiring large volumes of cleaned air to remove or dilute contaminants for satisfactory operations. There is a tendency, however, to design excessive airflow rates into cleanroom HVAC systems, due to factors such as design conservatism, lack of thorough understanding of airflow requirements, concerns about cleanliness reliability, and potential design and operational liabilities. Energy use of cleanroom environmental systems varies with system type and design, cleanroom functions, and the control of critical parameters such as temperature and humidity. In particular, cleanroom cleanliness requirements specified by cleanliness class have an impact on overall energy use. A previous study covering Europe and the US reveals annual cleanroom electricity usage for cooling and fan energy varies significantly depending on cleanliness class, and may account for up to three-quarters of total annual operating costs. A study on a semiconductor cleanroom in Japan found air delivery systems account for more than 30% of total power consumption. It is evident that the main factors dictating cleanroom operation energy include airflow rates and HVAC system efficiency. Improving energy efficiency in clean rooms may potentially contribute to significant savings in the initial costs of the facilities as well as operation and maintenance costs. For example, energy consumption by a typical chip manufacturer can be cut 40% or more, and the associated greenhouse emissions even more. Cleanroom HVAC systems provide huge opportunities for energy savings in the semiconductor industry. In addition to direct cost reductions in cleanroom investment and operation, energy-efficient designs can reduce maintenance costs, increase power reliability, improve time-to-market in cleanroom production, and improve environmental quality. Companies that use energy efficiency to lower costs and increase productivity can gain a competitive advantage and achieve a higher return on investment. In addition, energy-efficient cleanroom systems conserve energy and natural resources, heightening the company's reputation as an environmentally conscious leader in the community and the industry. A significant portion of energy use in cleanroom environmental systems is associated with recirculating air systems. We will review and analyze design factors and operational performance of airflow systems in ISO Class 5 clean rooms. We will also discuss benefits of efficient cleanroom airflow designs in conjunction with effective cleanroom contamination control. We will consider the following common recirculating air system designs: fan-tower (FT) with pressurized-plenum; distributed air handler unit (AHU); and fan-filter unit (FFU).

Xu, Tengfang

2004-07-29

46

Airflow elicits a spider's jump towards airborne prey. I. Airflow around a flying blowfly  

PubMed Central

The hunting spider Cupiennius salei uses airflow generated by flying insects for the guidance of its prey-capture jump. We investigated the velocity field of the airflow generated by a freely flying blowfly close to the flow sensors on the spider's legs. It shows three characteristic phases (I–III). (I) When approaching, the blowfly induces an airflow signal near the spider with only little fluctuation (0.013 ± 0.006 m s?1) and a strength that increases nearly exponentially with time (maximum: 0.164 ± 0.051 m s?1 s.d.). The spider detects this flow while the fly is still 38.4 ± 5.6 mm away. The fluctuation of the airflow above the sensors increases linearly up to 0.037 m s?1 with the fly's altitude. Differences in the time of arrival and intensity of the fly signal at different legs probably inform the spider about the direction to the prey. (II) Phase II abruptly follows phase I with a much higher degree of fluctuation (fluctuation amplitudes: 0.114 ± 0.050 m s?1). It starts when the fly is directly above the sensor and corresponds to the time-dependent flow in the wake below and behind the fly. Its onset indicates to the spider that its prey is now within reach and triggers its jump. The spider derives information on the fly's position from the airflow characteristics, enabling it to properly time its jump. The horizontal velocity of the approaching fly is reflected by the time of arrival differences (ranging from 0.038 to 0.108 s) of the flow at different legs and the exponential velocity growth rate (16–79 s?1) during phase I. (III) The air flow velocity decays again after the fly has passed the spider. PMID:22572032

Klopsch, Christian; Kuhlmann, Hendrik C.; Barth, Friedrich G.

2012-01-01

47

The Laminar Soot Processes (LSP)  

NASA Technical Reports Server (NTRS)

The Laminar Soot Processes (LSP) Experiment Mounting Structure (EMS) was used to conduct the LSP experiment on Combustion Module-1. The EMS was inserted into the nozzle on the EMS and ignited by a hot wire igniter. The flame and its soot emitting properties were studied.

2004-01-01

48

Laminar-flow flight experiments  

NASA Technical Reports Server (NTRS)

The flight testing conducted over the past 10 years in the NASA laminar-flow control (LFC) will be reviewed. The LFC program was directed towards the most challenging technology application, the high supersonic speed transport. To place these recent experiences in perspective, earlier important flight tests will first be reviewed to recall the lessons learned at that time.

Wagner, Richard D.; Maddalon, Dal V.; Bartlett, D. W.; Collier, F. S., Jr.; Braslow, A. L.

1989-01-01

49

Significance of nonrespiratory airflow during swallowing.  

PubMed

This study was designed to further our understanding of a potentially significant clinical event of negative nasal airflow near the end of the respiratory pause (inhibition) to accommodate swallowing. This negative flow, referred to as "SNIF," or swallow noninspiratory flow, occurs at the onset of airway reestablishment at the conclusion of the oropharyngeal swallow. Using simultaneous digital video fluoroscopic and nasal respiratory airflow recordings on 82 healthy adults (21-97 years old), the objectives of this study were to determine (1) the frequency of occurrence of SNIF during a 5-ml natural cup-drinking task, (2) differences in SNIF occurrence by age group, and (3) the temporal relationship between SNIF and other swallowing events. Results revealed that for most participants SNIF was observed in both swallowing trials. There was a statistically significant difference in SNIF occurrence by age category, with SNIF observed less frequently in the oldest participants. The peak onset of SNIF is closely related to the first release of contact between the soft palate and tongue base with the posterior pharyngeal wall and opening of the laryngeal vestibule. Based on this, and in agreement with previous investigators, we suggest that this negative flow may be related to a partial vacuum established by the relaxation of pharyngeal contraction near the conclusion of the pharyngeal swallow. The more frequent occurrence of SNIF in younger adults and less in older adults suggests a reduction in pharyngeal pressure associated with healthy aging. PMID:21748449

Brodsky, Martin B; McFarland, David H; Michel, Yvonne; Orr, Suzanne B; Martin-Harris, Bonnie

2012-06-01

50

Operational considerations for laminar flow aircraft  

NASA Technical Reports Server (NTRS)

Considerable progress has been made in the development of laminar flow technology for commercial transports during the NASA Aircraft Energy Efficiency (ACEE) laminar flow program. Practical, operational laminar flow control (LFC) systems have been designed, fabricated, and are undergoing flight testing. New materials, fabrication methods, analysis techniques, and design concepts were developed and show much promise. The laminar flow control systems now being flight tested on the NASA Jetstar aircraft are complemented by natural laminar flow flight tests to be accomplished with the F-14 variable-sweep transition flight experiment. An overview of some operational aspects of this exciting program is given.

Maddalon, Dal V.; Wagner, Richard D.

1986-01-01

51

Co-Articulatory Airflow Characteristics of Intervocalic Voiceless Plosives  

ERIC Educational Resources Information Center

A pneumotachographic investigation of intervocalic /p/, /t/ and /k/ was undertaken to isolate physiological parameters responsible for coarticulatory air-flow phenomena. Airflow was most sensitive during the /k/ closure phase. The dynamics of the closure phase for each place of articulation and their implications for pneumotachography are…

Barry, William; Kuenzel, Hermann

1975-01-01

52

Measuring Residential Ventilation System Airflows: Part 1 Laboratory  

E-print Network

1 Measuring Residential Ventilation System Airflows: Part 1 ­ Laboratory Evaluation of Airflow: residential, mechanical ventilation, measurement, ASHRAE 62.2, flow hood ABSTRACT Building codes increasingly require tighter homes and mechanical ventilation per ASHRAE Standard 62.2. These ventilation flows must

53

Computerized Acoustical Respiratory Phase Detection without Airflow Measurement  

E-print Network

Computerized Acoustical Respiratory Phase Detection without Airflow Measurement Zahra .K. Moussavi1):198:203, 2000. 2 ABSTRACT We sought to develop a simple, non-invasive acoustical method to detect respiratory of respiratory phases without using the measured airflow signal. Thus, acoustically monitoring breath

Moussavi, Zahra M. K.

54

Impacts of Fluid Dynamics Simulation in Study of Nasal Airflow Physiology and Pathophysiology in Realistic Human Three-Dimensional Nose Models  

PubMed Central

During the past decades, numerous computational fluid dynamics (CFD) studies, constructed from CT or MRI images, have simulated human nasal models. As compared to rhinomanometry and acoustic rhinometry, which provide quantitative information only of nasal airflow, resistance, and cross sectional areas, CFD enables additional measurements of airflow passing through the nasal cavity that help visualize the physiologic impact of alterations in intranasal structures. Therefore, it becomes possible to quantitatively measure, and visually appreciate, the airflow pattern (laminar or turbulent), velocity, pressure, wall shear stress, particle deposition, and temperature changes at different flow rates, in different parts of the nasal cavity. The effects of both existing anatomical factors, as well as post-operative changes, can be assessed. With recent improvements in CFD technology and computing power, there is a promising future for CFD to become a useful tool in planning, predicting, and evaluating outcomes of nasal surgery. This review discusses the possibilities and potential impacts, as well as technical limitations, of using CFD simulation to better understand nasal airflow physiology. PMID:23205221

Lee, Heow Peuh; Gordon, Bruce R.

2012-01-01

55

Experimental Investigation of the Induced Airflow of Corona Discharge  

NASA Astrophysics Data System (ADS)

In order to improve the acceleration effect of corona discharge acting on air, we present an experimental study on the induced airflow produced by corona discharge between two parallel electrodes. The parameters investigated are the type of electrodes, actuation voltage and the distance in the absence of free airflow. The induced flow velocity is measured directly in the accelerated region using the particle image velocimetry technology. The results show that if corona discharge is not developed into arc discharge, the induced airflow velocity increases nearly linearly with the applied voltage and the maximum induced airflow velocity near the needle electrode reaches 36 m/s. It is expected that in the future, the result can be referred to in the research about effect of active flow control to reach much higher induced airflow speed.

Huang, Yong; Zhang, Xin; Wang, Xun-Nian; Wang, Wan-Bo; Huang, Zong-Bo; Li, Hua-Xing

2013-09-01

56

On wind turbine power performance measurements at inclined airflow  

NASA Astrophysics Data System (ADS)

The average airflow inclination in complex terrain may be substantial. The airflow inclination affects wind turbine performance and also affects the cup anemometer being used in power performance measurements. In this article the overall dependence of the power curve on inclined airflow is analysed for its influence on both the wind turbine and the cup anemometer. The wind turbine performance analysis is based on results of measurements and theoretical calculations with the aeroelastic code HAWC coupled to a 3D actuator disc model for varying yaw angle. The cup anemometer analysis at inclined flow is based on an averaging of measured angular characteristics in a wind tunnel with the distribution of airflow inclination angles over time. The relative difference in annual energy production in terrain with inclined airflow compared with flat terrain is simulated for cup anemometers with theoretical optimal angular characteristics for two different definitions of wind speed, as well as for five commercial cup anemometers with measured angular characteristics. Copyright

Pedersen, T. F.

2004-07-01

57

Airflow patterns in a human nasal model  

SciTech Connect

Nasal airflow patterns were studied by using xenon 133 gas to image the course taken by air as it flowed through a plastic model of the human nasal cavity. The model was produced from the head of a human cadaver, and was anatomically correct. A needle catheter was used to infuse the radioactive xenon into a continuous flow of room air maintained through the model by a variable vacuum source connected to the nasopharynx. The radioactive gas was infused at one of five release sites in the nostril, and the distribution of the radioactivity was imaged in the sagittal plane with a scintillation camera. The data were organized to show the activity in six contiguous regions of the midnose. For each catheter, release site activity patterns were determined for three flow rates. The results of this experiment showed that both catheter position and flow rate had significant and reproducible effects on the distribution of radioactivity within the model.

Hornung, D.E.; Leopold, D.A.; Youngentob, S.L.; Sheehe, P.R.; Gagne, G.M.; Thomas, F.D.; Mozell, M.M.

1987-02-01

58

Theory of laminar viscous jets  

NASA Astrophysics Data System (ADS)

Results of recent theoretical studies of laminar jet flows of a viscous incompressible fluid are reviewed. In particular, attention is given to plane, fan-shaped, axisymmetric, and swirling jet flows; jet flows behind bodies; and slipstream jet flows. The discussion also covers dissipation of mechanical energy in jet flows, jet flows with a zero excess momentum, and asymptotic series expansions in the theory of jet flows.

Martynenko, O. G.; Korovkin, V. N.; Sokovishin, Iu. A.

59

Assembly of the Light-Harvesting Chlorophyll Antenna in the Green Alga Chlamydomonas reinhardtii Requires Expression of the TLA2-CpFTSY Gene1[C][W][OA  

PubMed Central

The truncated light-harvesting antenna2 (tla2) mutant of Chlamydomonas reinhardtii showed a lighter-green phenotype, had a lower chlorophyll (Chl) per-cell content, and higher Chl a/b ratio than corresponding wild-type strains. Physiological analyses revealed a higher intensity for the saturation of photosynthesis and greater Pmax values in the tla2 mutant than in the wild type. Biochemical analyses showed that the tla2 strain was deficient in the Chl a-b light-harvesting complex, and had a Chl antenna size of the photosystems that was only about 65% of that in the wild type. Molecular and genetic analyses showed a single plasmid insertion in the tla2 strain, causing a chromosomal DNA rearrangement and deletion/disruption of five nuclear genes. The TLA2 gene, causing the tla2 phenotype, was cloned by mapping the insertion site and upon complementation with each of the genes that were deleted. Successful complementation was achieved with the C. reinhardtii TLA2-CpFTSY gene, whose occurrence and function in green microalgae has not hitherto been investigated. Functional analysis showed that the nuclear-encoded and chloroplast-localized CrCpFTSY protein specifically operates in the assembly of the peripheral components of the Chl a-b light-harvesting antenna. In higher plants, a cpftsy null mutation inhibits assembly of both the light-harvesting complex and photosystem complexes, thus resulting in a seedling-lethal phenotype. The work shows that cpftsy deletion in green algae, but not in higher plants, can be employed to generate tla mutants. The latter exhibit improved solar energy conversion efficiency and photosynthetic productivity under mass culture and bright sunlight conditions. PMID:22114096

Kirst, Henning; García-Cerdán, Jose Gines; Zurbriggen, Andreas; Melis, Anastasios

2012-01-01

60

Optimization of VAV AHU Terminal Box Minimum Airflow  

E-print Network

Determining the optimal terminal box airflow is a complex process which is influenced by various factors, such as weather condition, supply air temperature, primary air fraction and internal load. A guideline for determination of a cost efficient...

Wang, Wei

2011-10-21

61

Laminar vortex shedding behind a cooled circular cylinder  

NASA Astrophysics Data System (ADS)

This paper addresses the functional demonstration of a hot air flow generator driven by convective heat transfer and the airflow behind a cooled circular cylinder in cross flow in the low velocity range. The wake flow was investigated experimentally using flow visualization, hot-wire anemometry, and laser Doppler anemometry. An evaluation of the free-stream velocity from the vortex shedding frequency was derived for the isothermal and non-isothermal cases and demonstrated using simple stroboscope measurements. The results confirm that cylinder cooling destabilizes the wake flow in air, i.e., the laminar steady regime can be changed into the vortex shedding regime, and the vortex shedding frequency increases as the cylinder temperature decreases. This thermal effect of cylinder cooling is consistent with its counterpart, the known effect of flow stabilization by cylinder heating. The effective temperature and effective Reynolds number concept have been further quantitatively evaluated, and the extension of their validity to the case of cooled cylinders has been confirmed.

Trávní?ek, Zden?k; Wang, An-Bang; Tu, Wen-Yun

2014-02-01

62

Derivation of airflow characteristics for back-draft dampers  

Microsoft Academic Search

In an effort to improve building energy and indoor air quality models, relations to describe the airflow characteristics of\\u000a back-draft dampers were determined. In particular, two equations were developed to represent the relationship between pressure\\u000a drop and airflow rate for one-blade and multi-blade back-draft dampers. The equation for multi-blade dampers was validated\\u000a by comparing the predicted results with available Air

Wei Guo; Darin W. Nutter

2010-01-01

63

Airflow patterns in a small subalpine basin  

NASA Astrophysics Data System (ADS)

A study of mean wind speeds and directions has been completed in the Snowy Range of Southern Wyoming, U.S.A. It was conducted in a subalpine ecosystem at an altitude of 3 200 m to 3 400 m above sea level during the summers of 1988 and 1989. Indexes of deformation and axes of asymmetry due to wind shaping of Engelmann spruce ( Picea engelmannii) and subalpine fir ( Abies lasiocarpa) are related to wind speeds and directions on a 100 m × 100 m grid spacing over the 300 ha research site. Isotach and airflow patterns are drawn to represent climatological near-ground-level winds. A statistical analysis of the wind data and deformation indexes indicates that the indexes estimated independently by three of the authors were not significantly different at the F0.025 level. Two methods of calculating wind speeds were applied. At lower mean wind speeds in Engelmann spruce, results from the Wade-Hewson method were not significantly different from the Griggs-Putnam method at the F0.025 level. In slightly higher wind speeds in subalpine fir, the Wade-Hewson method produced significantly lower wind speeds than the Griggs-Putnam method.

Wooldridge, G.; Musselman, R.; Connell, B.; Fox, D.

1992-03-01

64

Dynamics of airflow in a short inhalation  

PubMed Central

During a rapid inhalation, such as a sniff, the flow in the airways accelerates and decays quickly. The consequences for flow development and convective transport of an inhaled gas were investigated in a subject geometry extending from the nose to the bronchi. The progress of flow transition and the advance of an inhaled non-absorbed gas were determined using highly resolved simulations of a sniff 0.5 s long, 1 l s?1 peak flow, 364 ml inhaled volume. In the nose, the distribution of airflow evolved through three phases: (i) an initial transient of about 50 ms, roughly the filling time for a nasal volume, (ii) quasi-equilibrium over the majority of the inhalation, and (iii) a terminating phase. Flow transition commenced in the supraglottic region within 20 ms, resulting in large-amplitude fluctuations persisting throughout the inhalation; in the nose, fluctuations that arose nearer peak flow were of much reduced intensity and diminished in the flow decay phase. Measures of gas concentration showed non-uniform build-up and wash-out of the inhaled gas in the nose. At the carina, the form of the temporal concentration profile reflected both shear dispersion and airway filling defects owing to recirculation regions. PMID:25551147

Bates, A. J.; Doorly, D. J.; Cetto, R.; Calmet, H.; Gambaruto, A. M.; Tolley, N. S.; Houzeaux, G.; Schroter, R. C.

2015-01-01

65

Dynamics of airflow in a short inhalation  

E-print Network

During a rapid inhalation, such as a sniff, the flow in the airways accelerates and decays quickly. The consequences for flow development and convective trans- port of an inhaled gas were investigated in a subject geometry extending from the nose to the bronchi. The progress of flow transition and the advance of an inhaled non-absorbed gas were determined using highly resolved simulations of a sniff 0.5 s long, 1 litre per second peak flow, 364 ml inhaled volume. In the nose, the distribution of airflow evolved through three phases: (i) an initial transient of about 50 ms, roughly the filling time for a nasal volume, (ii) quasi-equilibrium over the majority of the inhalation, and (iii) a terminating phase. Flow transition commenced in the supraglottic region within 20ms, resulting in large- amplitude fluctuations persisting throughout the inhalation; in the nose, fluctuations that arose nearer peak flow were of much reduced intensity and diminished in the flow decay phase. Measures of gas concentration showed...

Bates, Alister; Cetto, Raul; Calmet, Hadrien; Gambaruto, Alberto; Tolley, Neil; Houzeaux, Guillaume; Schroter, Robert

2015-01-01

66

Burning Laminar Jet Diffusion Flame  

NASA Technical Reports Server (NTRS)

Study of the downlink data from the Laminar Soot Processes (LSP) experiment quickly resulted in discovery of a new mechanism of flame extinction caused by radiation of soot. Scientists found that the flames emit soot sooner than expected. These findings have direct impact on spacecraft fire safety, as well as the theories predicting the formation of soot -- which is a major factor as a pollutant and in the spread of unwanted fires. This sequence was taken July 15, 1997, MET:14/10:34 (approximate) and shows the ignition and extinction of this flame. LSP investigated fundamental questions regarding soot, a solid byproduct of the combustion of hydrocarbon fuels. The experiment was performed using a laminar jet diffusion flame, which is created by simply flowing fuel -- like ethylene or propane -- through a nozzle and igniting it, much like a butane cigarette lighter. The LSP principal investigator was Gerard Faeth, University of Michigan, Arn Arbor. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). LSP results led to a reflight for extended investigations on the STS-107 research mission in January 2003. Advanced combustion experiments will be a part of investigations planned for the International Space Station. (518KB, 20-second MPEG, screen 160 x 120 pixels; downlinked video, higher quality not available) A still JPG composite of this movie is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300182.html.

2003-01-01

67

Laminar Jet Diffusion Flame Burning  

NASA Technical Reports Server (NTRS)

Study of the downlink data from the Laminar Soot Processes (LSP) experiment quickly resulted in discovery of a new mechanism of flame extinction caused by radiation of soot. Scientists found that the flames emit soot sooner than expected. These findings have direct impact on spacecraft fire safety, as well as the theories predicting the formation of soot -- which is a major factor as a pollutant and in the spread of unwanted fires. This sequence, using propane fuel, was taken STS-94, July 4 1997, MET:2/05:30 (approximate). LSP investigated fundamental questions regarding soot, a solid byproduct of the combustion of hydrocarbon fuels. The experiment was performed using a laminar jet diffusion flame, which is created by simply flowing fuel-like ethylene or propane -- through a nozzle and igniting it, much like a butane cigarette lighter. The LSP principal investigator was Gerard Faeth, University of Michigan, Arn Arbor. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). LSP results led to a reflight for extended investigations on the STS-107 research mission in January 2003. Advanced combustion experiments will be a part of investigations planned for the International Space Station. (983KB, 9-second MPEG, screen 320 x 240 pixels; downlinked video, higher quality not available) A still JPG composite of this movie is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300184.html.

2003-01-01

68

Laminar-flow wind tunnel experiments  

NASA Technical Reports Server (NTRS)

Although most of the laminar flow airfoils recently developed at the NASA Langley Research Center were intended for general aviation applications, low-drag airfoils were designed for transonic speeds and wind tunnel performance tested. The objective was to extend the technology of laminar flow to higher Mach and Reynolds numbers and to swept leading edge wings representative of transport aircraft to achieve lower drag and significantly improved operation costs. This research involves stabilizing the laminar boundary layer through geometric shaping (Natural Laminar Flow, NLF) and active control involving the removal of a portion of the laminar boundary layer (Laminar-Flow Control, LFC), either through discrete slots or perforated surface. Results show that extensive regions of laminar flow with large reductions in skin friction drag can be maintained through the application of passive NLF boundary-layer control technologies to unswept transonic wings. At even greater extent of laminar flow and reduction in the total drag level can be obtained on a swept supercritical airfoil with active boundary layer-control.

Harvey, William D.; Harris, Charles D.; Sewall, William G.; Stack, John P.

1989-01-01

69

Minimum airflow reset of single-duct VAV terminal boxes  

NASA Astrophysics Data System (ADS)

Single duct Variable Air Volume (VAV) systems are currently the most widely used type of HVAC system in the United States. When installing such a system, it is critical to determine the minimum airflow set point of the terminal box, as an optimally selected set point will improve the level of thermal comfort and indoor air quality (IAQ) while at the same time lower overall energy costs. In principle, this minimum rate should be calculated according to the minimum ventilation requirement based on ASHRAE standard 62.1 and maximum heating load of the zone. Several factors must be carefully considered when calculating this minimum rate. Terminal boxes with conventional control sequences may result in occupant discomfort and energy waste. If the minimum rate of airflow is set too high, the AHUs will consume excess fan power, and the terminal boxes may cause significant simultaneous room heating and cooling. At the same time, a rate that is too low will result in poor air circulation and indoor air quality in the air-conditioned space. Currently, many scholars are investigating how to change the algorithm of the advanced VAV terminal box controller without retrofitting. Some of these controllers have been found to effectively improve thermal comfort, indoor air quality, and energy efficiency. However, minimum airflow set points have not yet been identified, nor has controller performance been verified in confirmed studies. In this study, control algorithms were developed that automatically identify and reset terminal box minimum airflow set points, thereby improving indoor air quality and thermal comfort levels, and reducing the overall rate of energy consumption. A theoretical analysis of the optimal minimum airflow and discharge air temperature was performed to identify the potential energy benefits of resetting the terminal box minimum airflow set points. Applicable control algorithms for calculating the ideal values for the minimum airflow reset were developed and applied to actual systems for performance validation. The results of the theoretical analysis, numeric simulations, and experiments show that the optimal control algorithms can automatically identify the minimum rate of heating airflow under actual working conditions. Improved control helps to stabilize room air temperatures. The vertical difference in the room air temperature was lower than the comfort value. Measurements of room CO2 levels indicate that when the minimum airflow set point was reduced it did not adversely affect the indoor air quality. According to the measured energy results, optimal control algorithms give a lower rate of reheating energy consumption than conventional controls.

Cho, Young-Hum

70

Resistance to forced airflow through layers of composting organic material.  

PubMed

The objective of this study was to adjust equations to estimate the static pressure gradient of airflow through layers of organic residues submitted to two stages of biochemical degradation, and to evaluate the static pressure drop of airflow thought the material layer. Measurements of static pressure drop in the layers of sugarcane bagasse and coffee husks mixed with poultry litter on day 0 and after 30days of composting were performed using a prototype with specific airflow rates ranging from 0.02 to 0.13m(3)s(-1)m(-2). Static pressure gradient and specific airflow rate data were properly fit to the Shedd, Hukill & Ives and Ergun models, which may be used to predict the static pressure gradient of air to be blown through the organic residue layers. However, the Shedd model was that which best represented the phenomenon studied. The static pressure drop of airflow increased as a power of the material layer thickness and showed tendency for decreasing with the biochemical degradation time of the organic material. PMID:25536861

Teixeira, Denis Leocádio; Matos, Antonio Teixeira de; Melo, Evandro de Castro

2015-02-01

71

The effect of laminar air flow and door openings on operating room contamination.  

PubMed

We evaluate the association of laminar airflow (LAF) and OR traffic with intraoperative contamination rates. Two sterile basins were placed in each room during 81 cases, one inside and one outside the LAF. One Replicate Organism Detection and Counting (RODAC) plate from each basin was sent for culture at successive 30-minute intervals from incision time until wound closure. At successive 30-minute intervals more plates were contaminated outside than inside the LAF. A negative binomial model showed that the bacteria colony forming units (CFU) depended on whether there were any door openings (P=0.02) and the presence of LAF (P=0.003). LAF decreases CFU by 36.6%. LAF independently reduces the risk of contamination and microbial counts for surgeries lasting 90 minutes or less. PMID:23890828

Smith, Eric B; Raphael, Ibrahim J; Maltenfort, Mitchell G; Honsawek, Sittisak; Dolan, Kyle; Younkins, Elizabeth A

2013-10-01

72

Airflow Hazard Visualization for Helicopter Pilots: Flight Simulation Study Results  

NASA Technical Reports Server (NTRS)

Airflow hazards such as vortices or low level wind shear have been identified as a primary contributing factor in many helicopter accidents. US Navy ships generate airwakes over their decks, creating potentially hazardous conditions for shipboard rotorcraft launch and recovery. Recent sensor developments may enable the delivery of airwake data to the cockpit, where visualizing the hazard data may improve safety and possibly extend ship/helicopter operational envelopes. A prototype flight-deck airflow hazard visualization system was implemented on a high-fidelity rotorcraft flight dynamics simulator. Experienced helicopter pilots, including pilots from all five branches of the military, participated in a usability study of the system. Data was collected both objectively from the simulator and subjectively from post-test questionnaires. Results of the data analysis are presented, demonstrating a reduction in crash rate and other trends that illustrate the potential of airflow hazard visualization to improve flight safety.

Aragon, Cecilia R.; Long, Kurtis R.

2005-01-01

73

Airflow studies in a forced ventilated chamber with low partitions  

SciTech Connect

A climate chamber was used to study experimentally the airflow characteristics in a ventilated space with low partitions. Two types of commonly used air distribution devices were selected for the study--a ceiling diffuser and side grille systems. A total of 16 tests were performed using the two diffusers with partition heights varying up to 1.8 m (5.91 ft) above floor level. From the measured results, the thermal comfort indices were assessed. A stabilization effect of airflow was found when the partition height reached 1.8 m (5.91 ft). Local draft risk was located in the occupied zone. Also, the modified Archimedes number proposed by Jackman (1990) was used to describe the indoor airflow in the absence of a workable design guide for partitioned spaces.

Chow, W.K.; Tsui, K.F. [Hong Kong Polytechnic Univ. (Hong Kong). Dept. of Building Services Engineering

1995-12-31

74

Research in Natural Laminar Flow and Laminar-Flow Control, part 3  

NASA Technical Reports Server (NTRS)

Part 3 of the Symposium proceedings contains papers addressing advanced airfoil development, flight research experiments, and supersonic transition/laminar flow control research. Specific topics include the design and testing of natural laminar flow (NLF) airfoils, NLF wing gloves, and NLF nacelles; laminar boundary-layer stability over fuselage forebodies; the design of low noise supersonic/hypersonic wind tunnels; and boundary layer instability mechanisms on swept leading edges at supersonic speeds.

Hefner, Jerry N. (compiler); Sabo, Frances E. (compiler)

1987-01-01

75

Unidirectional pulmonary airflow patterns in the savannah monitor lizard.  

PubMed

The unidirectional airflow patterns in the lungs of birds have long been considered a unique and specialized trait associated with the oxygen demands of flying, their endothermic metabolism and unusual pulmonary architecture. However, the discovery of similar flow patterns in the lungs of crocodilians indicates that this character is probably ancestral for all archosaurs--the group that includes extant birds and crocodilians as well as their extinct relatives, such as pterosaurs and dinosaurs. Unidirectional flow in birds results from aerodynamic valves, rather than from sphincters or other physical mechanisms, and similar aerodynamic valves seem to be present in crocodilians. The anatomical and developmental similarities in the primary and secondary bronchi of birds and crocodilians suggest that these structures and airflow patterns may be homologous. The origin of this pattern is at least as old as the split between crocodilians and birds, which occurred in the Triassic period. Alternatively, this pattern of flow may be even older; this hypothesis can be tested by investigating patterns of airflow in members of the outgroup to birds and crocodilians, the Lepidosauromorpha (tuatara, lizards and snakes). Here we demonstrate region-specific unidirectional airflow in the lungs of the savannah monitor lizard (Varanus exanthematicus). The presence of unidirectional flow in the lungs of V.?exanthematicus thus gives rise to two possible evolutionary scenarios: either unidirectional airflow evolved independently in archosaurs and monitor lizards, or these flow patterns are homologous in archosaurs and V.?exanthematicus, having evolved only once in ancestral diapsids (the clade encompassing snakes, lizards, crocodilians and birds). If unidirectional airflow is plesiomorphic for Diapsida, this respiratory character can be reconstructed for extinct diapsids, and evolved in a small ectothermic tetrapod during the Palaeozoic era at least a hundred million years before the origin of birds. PMID:24336209

Schachner, Emma R; Cieri, Robert L; Butler, James P; Farmer, C G

2014-02-20

76

A faster 'transition' to laminar flow  

NASA Technical Reports Server (NTRS)

A discussion is given of the ongoing research related to laminar flow airfoils, nacelles, and wings where the laminar flow is maintained by a favorable pressure gradient, surface suction or a combination of the two. Design methologies for natural laminar flow airfoil sections and wings for both low and high speed applications are outlined. Tests of a 7-foot chord, 23-deg sweep laminar flow-control airfoil at high subsonic Mach numbers are described, along with the associated stability theory used to design the suction system. The state-of-the-art of stability theory is simply stated and a typical calculation illustrated. In addition, recent computer simulations of transition using the time dependent Navier-Stokes equations are briefly described. Advances in wind tunnel capabilities and instrumentation will be reviewed, followed by the presentation of a few results from both wind tunnels and flight. Finally, some suggestions for future work will complete the paper.

Bobbitt, P. J.; Waggoner, E. G.; Harvey, W. D.; Dagenhart, J. R.

1985-01-01

77

Dynamics of secondary airflow and sediment transport over and in the lee of transverse dunes  

Microsoft Academic Search

Recent research literature on secondary airflow and sediment transport patterns over flow-transverse dunes is reviewed. Various issues surrounding the behaviour, modelling and sedimentological implications of near-surface airflow dynamics over dunes are discussed, including: the Law of the Wall; the Jackson and Hunt airflow model; the effects of streamline compression, acceleration and curvature on stoss slope shear stress; and, in particular,

Ian J. Walker; William G. Nicklingb

2002-01-01

78

Severity of Airflow Limitation Is Associated with Severity of Airway Inflammation in Smokers  

Microsoft Academic Search

To investigate the relationship between airflow limitation and airway inflammation in smokers, we examined paraffin-embedded bronchial biopsies obtained from 30 smokers: 10 with severe airflow limitation, eight with mild\\/moderate airflow limitation, and 12 control smokers with normal lung function. Histochemical and immunohistochemical methods were performed to assess the number of inflammatory cells in the subepithelium and the expression of CC

ANTONINO DI STEFANO; ARMANDO CAPELLI; MIRCO LUSUARDI; PIERO BALBO; CINZIA VECCHIO; PIERO MAESTRELLI; CRISTINA E. MAPP; LEONARDO M. FABBRI; CLAUDIO F. DONNER; MARINA SAETTA

1998-01-01

79

A Coupled Airflow-and-Energy Simulation Program for Indoor Thermal Environment Studies (RP-927)  

E-print Network

1 A Coupled Airflow-and-Energy Simulation Program for Indoor Thermal Environment Studies (RP-927 the thermal environment in a house and an atrium. The coupled flow-and-energy program is recommended to calculate unsteady room airflow and thermal environment. Our study has developed a coupled airflow-and-energy

Chen, Qingyan "Yan"

80

Control of airflow about a high energy laser turret  

Microsoft Academic Search

A high energy laser system inflicts damage on a target by radiating large amounts of thermal energy onto a small area. Airflow about the laser turret, which is located on top of the aircraft fuselage, is unsteady and causes problems in beam control. The problems are jitter, which is vibration of the laser beam, and optical path distortions. The theory

A. M. Mandigo

1980-01-01

81

Calibration of a novel airflow transducer for use in pneumotachography  

Microsoft Academic Search

Wave energy research at Coventry University (formerly Coventry Lanchester Polytechnic) led to the development of the Clam wave energy converter. In operation the Clam allows wave motion to produce air displacement and, through the use of a Wells turbine, electricity may be generated. The need to test the Clam at model scale led to the development of an airflow transducer

E. F. J. Coolen; M. J. West; P. R. S. White

1999-01-01

82

Air-flow regulation system for a coal gasifier  

DOEpatents

An improved air-flow regulator for a fixed-bed coal gasifier is provided which allows close air-flow regulation from a compressor source even though the pressure variations are too rapid for a single primary control loop to respond. The improved system includes a primary controller to control a valve in the main (large) air supply line to regulate large slow changes in flow. A secondary controller is used to control a smaller, faster acting valve in a secondary (small) air supply line parallel to the main line valve to regulate rapid cyclic deviations in air flow. A low-pass filter with a time constant of from 20 to 50 seconds couples the output of the secondary controller to the input of the primary controller so that the primary controller only responds to slow changes in the air-flow rate, the faster, cyclic deviations in flow rate sensed and corrected by the secondary controller loop do not reach the primary controller due to the high frequency rejection provided by the filter. This control arrangement provides at least a factor of 5 improvement in air-flow regulation for a coal gasifier in which air is supplied by a reciprocating compressor through a surge tank.

Fasching, George E. (Morgantown, WV)

1984-01-01

83

Volume average technique for turbulent flow simulation and its application to room airflow prediction  

NASA Astrophysics Data System (ADS)

Fluid motion turbulence is one of the most important transport phenomena occurring in engineering applications. Although turbulent flow is governed by a set of conservation equations for momentum, mass, and energy, a Direct Numerical Simulation (DNS) of the flow by solving these equations to include the finest scale motions is impossible due to the extremely large computer resources required. On the other hand, the Reynolds Averaged Modelling (RAM) method has many limitations which hinder its applications to turbulent flows of practical significance. Room airflow featuring co- existence of laminar and turbulence regimes is a typical example of a flow which is difficult to handle with the RAM method. A promising way to avoid the difficulty of the DNS method and the limitation of the RAM method is to use the Large Eddy Simulation (LES) method. In the present thesis, the drawbacks of previously developed techniques for the LES method, particularly those associated with the SGS modelling, are identified. Then a new so called Volume Average Technique (VAT) for turbulent flow simulation is proposed. The main features of the VAT are as follows: (1) The volume averaging approach instead of the more common filtering approach is employed to define solvable scale fields, so that coarse- graining in the LES and space discretization of the numerical scheme are achieved in a single procedure. (2) All components of the SGS Reynolds stress and SGS turbulent heat flux are modelled dynamically using the newly proposed Functional Scale Similarity (FSS) SGS model. The model is superior to many previously developed SGS models in that it can be applied to highly inhomogeneous and/or anisotropic, weak or multi-regime turbulent flows using a relatively coarse grid. (3) The so called SGS turbulent diffusion is identified and modelled as a separate mechanism to that of the SGS turbulent flux represented by the SGS Reynolds stress and SGS turbulent heat flux. The SGS turbulent diffusion is defined in the coarse-graining procedure, and responsible for most of the energy dissipation. (4) A new 3-D collocated scheme for the solution of viscous incompressible fluid flow, based on the SIMPLE and fractional-step methods is developed for the LES. Benchmark tests of the VAT are performed based on 2-D and 3-D lid-driven and 3-D buoyancy-driven cavity flows. Finally, as an example of a practical calculation, the VAT is applied to the LES of airflow in an enclosed air- conditioned room with a wall-mounted cooling inlet and an outlet on the opposite wall.

Huang, Xianmin

84

Change in airflow among patients with asthma discussing relationship problems with their partners.  

PubMed

This study examined the covariation of negative emotions with airflow among 48 persons with asthma and their partners as they discussed relationship problems. Measures included self-reported questionnaires, airflow and behavior coded from videotaped discussions. Significantly increased self-reported hostility and statistically but not clinically significant declines in airflow were found post- versus pre-discussion. Self-reported responses to asthma symptoms of more anger and less loneliness predicted lower post-discussion airflow after accounting for pre-discussion airflow. The use of effort-independent measures of airflow and autonomic nervous system monitoring may inform future research regarding the physiological mechanisms through which mood and behavior affect airflow. PMID:19687108

Schmaling, Karen B; Afari, Niloofar; Hops, Hyman; Barnhart, Scott; Buchwald, Dedra

2009-09-01

85

Laminar Heating Validation of the OVERFLOW Code  

NASA Technical Reports Server (NTRS)

OVERFLOW, a structured finite difference code, was applied to the solution of hypersonic laminar flow over several configurations assuming perfect gas chemistry. By testing OVERFLOW's capabilities over several configurations encompassing a variety of flow physics a validated laminar heating was produced. Configurations tested were a flat plate at 0 degrees incidence, a sphere, a compression ramp, and the X-38 re-entry vehicle. This variety of test cases shows the ability of the code to predict boundary layer flow, stagnation heating, laminar separation with re-attachment heating, and complex flow over a three-dimensional body. In addition, grid resolutions studies were done to give recommendations for the correct number of off-body points to be applied to generic problems and for wall-spacing values to capture heat transfer and skin friction. Numerical results show good comparison to the test data for all the configurations.

Lillard, Randolph P.; Dries, Kevin M.

2005-01-01

86

Laminar Flame Speeds of Moist Syngas Mixtures  

SciTech Connect

This work experimentally investigates the effect of the presence of water vapor on the laminar flame speeds of moist syngas/air mixtures using the counterflow twin-flame configuration. The experimental results presented here are for fuel lean syngas mixtures with molar percentage of hydrogen in the hydrogen and carbon monoxide mixture varying from 5% to 100%, for an unburned mixture temperature of 323 K, and under atmospheric pressure. At a given equivalence ratio, the effect of varying amount of water vapor addition on the measured laminar flame speed is demonstrated. The experimental laminar flame speeds are also compared with computed values using chemical kinetic mechanisms reported in the literature. It is found that laminar flame speed varies non-monotonically with addition of water for the carbon monoxide rich mixtures. It first increases with increasing amount of water addition, reaches a maximum value, and then decreases. An integrated reaction path analysis is further conducted to understand the controlling mechanism responsible for the non-monotonic variation in laminar flame speed due to water addition. On the other hand, for higher values of H{sub 2}/CO ratio the laminar flame speed monotonically decreases with increasing water addition. It is shown that the competition between the chemical and thermal effects of water addition leads to the observed response. Furthermore, reaction rate sensitivity analysis as well as binary diffusion coefficient sensitivity analysis are conducted to identify the possible sources of discrepancy between the experimental and predicted values. The sensitivity results indicate that the reaction rate constant of H{sub 2} + OH = H{sub 2}O + H is worth revisiting and refinement of binary diffusion coefficient data of N{sub 2}–H{sub 2}O, N{sub 2}–H{sub 2}, and H{sub 2}–H{sub 2}O pairs can be considered.

Das, A. K.; Kumar, K.; Zhang, Z.; Sung, C. J.

2011-01-01

87

Transient airflow structures and particle transport in a sequentially branching lung airway model  

NASA Astrophysics Data System (ADS)

Considering oscillatory laminar incompressible three-dimensional flow in triple planar and nonplanar bifurcations representing generations three to six of the human respiratory system, air flow fields and micron-particle transport have been simulated under normal breathing and high-frequency ventilation (HFV) conditions. A finite-volume code (CFX4.3 from AEA Technology, Pittsburgh, PA) and its user-enhanced FORTRAN programs were validated with experimental velocity data points for a single bifurcation. The airflow structures and micron-particle motion in the triple bifurcations were analyzed for a representative normal breathing cycle as well as HFV condition. While both the peak inspiratory and expiratory velocity profiles for the low Womersley case (?=0.93) agree well with those of instantaneously equivalent steady-state cases, some differences can be observed between flow acceleration and deceleration at off-peak periods or near flow reversal, especially during inspiratory flow. Similarly, the basic features of instantaneous particle motion closely resemble the steady-state case at equivalent inlet Reynolds numbers. The preferential concentration of particles caused by the coherent vortical structures was found in both inhalation and exhalation; however, it is more complicated during expiration. The effects of Womersley number and non-planar geometries as well as the variations in secondary flow intensity plus pressure drops across various bifurcations under normal breathing and HFV conditions were analyzed as well. This work may elucidate basic physical insight of aerosol transport relevant in dosimetry-and-health-effect studies as well as for drug aerosol delivery analyses.

Zhang, Z.; Kleinstreuer, C.

2002-02-01

88

Flow/Soot-Formation Interactions in Nonbuoyant Laminar Diffusion Flames  

NASA Technical Reports Server (NTRS)

This is the final report of a research program considering interactions between flow and soot properties within laminar diffusion flames. Laminar diffusion flames were considered because they provide model flame systems that are far more tractable for theoretical and experimental studies than more practical turbulent diffusion flames. In particular, understanding the transport and chemical reaction processes of laminar flames is a necessary precursor to understanding these processes in practical turbulent flames and many aspects of laminar diffusion flames have direct relevance to turbulent diffusion flames through application of the widely recognized laminar flamelet concept of turbulent diffusion flames. The investigation was divided into three phases, considering the shapes of nonbuoyant round laminar jet diffusion flames in still air, the shapes of nonbuoyant round laminar jet diffusion flames in coflowing air, and the hydrodynamic suppression of soot formation in laminar diffusion flames.

Dai, Z.; Lin, K.-C.; Sunderland, P. B.; Xu, F.; Faeth, G. M.

2002-01-01

89

Airflow and Particle Transport in the Human Respiratory System  

NASA Astrophysics Data System (ADS)

Airflows in the nasal cavities and oral airways are rather complex, possibly featuring a transition to turbulent jet-like flow, recirculating flow, Dean's flow, vortical flows, large pressure drops, prevailing secondary flows, and merging streams in the case of exhalation. Such complex flows propagate subsequently into the tracheobronchial airways. The underlying assumptions for particle transport and deposition are that the aerosols are spherical, noninteracting, and monodisperse and deposit upon contact with the airway surface. Such dilute particle suspensions are typically modeled with the Euler-Lagrange approach for micron particles and in the Euler-Euler framework for nanoparticles. Micron particles deposit nonuniformly with very high concentrations at some local sites (e.g., carinal ridges of large bronchial airways). In contrast, nanomaterial almost coats the airway surfaces, which has implications of detrimental health effects in the case of inhaled toxic nanoparticles. Geometric airway features, as well as histories of airflow fields and particle distributions, may significantly affect particle deposition.

Kleinstreuer, C.; Zhang, Z.

2010-01-01

90

Computational Investigation of Dynamic Glottal Aperture Effects on Respiratory Airflow  

NASA Astrophysics Data System (ADS)

The periodic movement of the glottal aperture (vocal folds) during tidal breathing has been long recognized as a factor in altering the airflow dynamics in the tracheobrnchial region. The potential influence from these altered flow structures on the transport and deposition of inhaled particles is not known. However, studies devoted to this dynamic physiological feature are scarce due to the complex anatomy in of the larynx and numerical challenges in simulating dynamic geometries. In this study, a high-fidelity immersed boundary solver is used to investigate this problem. A 3D human oral-larynx-lung model is firstly reconstructed from MRI data. The role of the vocal fold movement and associated airflow characteristics such as vortex shedding, Coanda effect etc. during inhalation and exhalation are then numerically studied.

Xi, Jinxiang; Yan, Hong; Dong, Haibo

2008-11-01

91

Severe airflow obstruction in vertically acquired HIV infection  

PubMed Central

It is becoming increasingly clear that human immunodeficiency virus (HIV) infection, either independently or in concert with opportunistic infections like pulmonary tuberculosis, is a risk factor for the development of chronic airflow limitation. In the majority of patients the etiology of this obstructive ventilatory defect is multifactorial. Post-infectious obliterative bronchiolitis, post-tuberculous lung damage (including bronchiectasis), immune reconstitution and the direct effects of HIV viral infection may all play a role. With increases in life expectancy and decreases in infectious complications in patients taking antiretroviral medications, the importance of HIV-associated chronic lung disease as a cause of pulmonary disability is likely to increase. This is particularly relevant in regions like sub-Saharan Africa, where both HIV infection and tuberculosis are highly prevalent. Here, to illustrate the complexity of this interaction, we present the case of a 15-year-old girl with vertically acquired HIV infection, multiple episodes of pulmonary infection, and severe airflow obstruction.

Calligaro, Gregory L; Esmail, Aliasgar; Gray, Diane M

2014-01-01

92

Three-dimensional mapping of airflow over dunes  

NASA Astrophysics Data System (ADS)

Similar to the way a river, flowing across Earth's surface, influences sediment transport and shaping of the landscape, coastal winds, which flow over dunes, affect how the dune shapes evolve and how sand is transported along the coast. Wind flow over dunes has been extensively studied, but in most cases, that research has been two-dimensional and focused on straight dunes with smooth slopes and no vegetation or other features that might affect how airflow separates at the crest of the dune.

Balcerak, Ernie

2013-05-01

93

Airflow Simulations around OA Intake Louver with Electronic Velocity Sensors  

SciTech Connect

It is important to control outdoor airflow rates into HVAC systems in terms of energy conservation and healthy indoor environment. Technologies are being developed to measure outdoor air (OA) flow rates through OA intake louvers on a real time basis. The purpose of this paper is to investigate the airflow characteristics through an OA intake louver numerically in order to provide suggestions for sensor installations. Airflow patterns are simulated with and without electronic air velocity sensors within cylindrical probes installed between louver blades or at the downstream face of the louver. Numerical results show quite good agreements with experimental data, and provide insights regarding measurement system design. The simulations indicate that velocity profiles are more spatially uniform at the louver outlet relative to between louver blades, that pressure drops imposed by the sensor bars are smaller with sensor bars at the louver outlet, and that placement of the sensor bars between louver blades substantially increases air velocities inside the louver. These findings suggest there is an advantage to placing the sensor bars at the louver outlet face.

Han, Hwataik; Sullivan, Douglas P.; Fisk, William J.

2009-04-01

94

Research in Natural Laminar Flow and Laminar-Flow Control, part 1  

NASA Technical Reports Server (NTRS)

Since the mid 1970's, NASA, industry, and universities have worked together to conduct important research focused at developing laminar flow technology that could reduce fuel consumption for general aviation, commuter, and transport aircraft by as much as 40 to 50 percent. The symposium was planned in view of the recent accomplishments within the areas of laminar flow control and natural laminar flow, and the potential benefits of laminar flow technology to the civil and military aircraft communities in the United States. Included were technical sessions on advanced theory and design tool development; wind tunnel and flight research; transition measurement and detection techniques; low and high Reynolds number research; and subsonic and supersonic research.

Hefner, Jerry N. (compiler); Sabo, Frances E. (compiler)

1987-01-01

95

Class II (laminar flow) biological safety cabinet  

Microsoft Academic Search

A microbiological survey of the effectiveness of class II (laminar flow) 'safety' cabinets found in the UK in the last six years is recorded. Only two of the nine units tested approached the containment of aerosols achieved by a good class I (exhaust protective) cabinet. The others were potentially hazardous if used with pathogenic material. The National Sanitation Foundation and

S W Newsom

1979-01-01

96

Soot Formation In Laminar Inverse Diffusion Flames  

Microsoft Academic Search

Soot formation in laminar ethylene inverse diffusion flames has been investigated experimentally and modeled. Soot volume fraction and temperature measurements have been made and compared to numerical predictions using a soot formation model previously applied to normal diffusion flames. The inverse flame configuration serves as a good test of the applicability of the model and is relevant to practical combustor

D. B. MAKEL; I. M. KENNEDY

1994-01-01

97

Grooved surfaces for laminar drag reduction  

NASA Astrophysics Data System (ADS)

Laminar, pressure driven flows through annuli have been analyzed. It has been shown that a significant reduction of pressure losses can be accomplished using longitudinal grooves. The optimum form of the grooves that results in the maximum possible drag reduction has been determined.

Floryan, J. M.; Moradi, H. V.

2012-09-01

98

Laminar Entrained Flow Reactor (Fact Sheet)  

SciTech Connect

The Laminar Entrained Flow Reactor (LEFR) is a modular, lab scale, single-user reactor for the study of catalytic fast pyrolysis (CFP). This system can be employed to study a variety of reactor conditions for both in situ and ex situ CFP.

Not Available

2014-02-01

99

Soot formation in laminar diffusion flames  

Microsoft Academic Search

Laminar, sooting, coflow diffusion flames at atmospheric pressure have been studied experimentally and theoretically as a function of fuel dilution by inert nitrogen. The flames have been investigated with laser diagnostics. Laser extinction has been used to calibrate the experimental soot volume fractions and an improved gating method has been implemented in the laser-induced incandescence (LII) measurements resulting in differences

M. D. Smooke; M. B. Long; B. C. Connelly; M. B. Colket; R. J. Hall

2005-01-01

100

Optimal determination of respiratory airflow patterns using a nonlinear multicompartment model for a lung mechanics system.  

PubMed

We develop optimal respiratory airflow patterns using a nonlinear multicompartment model for a lung mechanics system. Specifically, we use classical calculus of variations minimization techniques to derive an optimal airflow pattern for inspiratory and expiratory breathing cycles. The physiological interpretation of the optimality criteria used involves the minimization of work of breathing and lung volume acceleration for the inspiratory phase, and the minimization of the elastic potential energy and rapid airflow rate changes for the expiratory phase. Finally, we numerically integrate the resulting nonlinear two-point boundary value problems to determine the optimal airflow patterns over the inspiratory and expiratory breathing cycles. PMID:22719793

Li, Hancao; Haddad, Wassim M

2012-01-01

101

Optimal Determination of Respiratory Airflow Patterns Using a Nonlinear Multicompartment Model for a Lung Mechanics System  

PubMed Central

We develop optimal respiratory airflow patterns using a nonlinear multicompartment model for a lung mechanics system. Specifically, we use classical calculus of variations minimization techniques to derive an optimal airflow pattern for inspiratory and expiratory breathing cycles. The physiological interpretation of the optimality criteria used involves the minimization of work of breathing and lung volume acceleration for the inspiratory phase, and the minimization of the elastic potential energy and rapid airflow rate changes for the expiratory phase. Finally, we numerically integrate the resulting nonlinear two-point boundary value problems to determine the optimal airflow patterns over the inspiratory and expiratory breathing cycles. PMID:22719793

Li, Hancao; Haddad, Wassim M.

2012-01-01

102

Real-time visualization and analysis of airflow field by use of digital holography  

NASA Astrophysics Data System (ADS)

The measurement and analysis of airflow field is very important in fluid dynamics. For airflow, smoke particles can be added to visually observe the turbulence phenomena by particle tracking technology, but the effect of smoke particles to follow the high speed airflow will reduce the measurement accuracy. In recent years, with the advantage of non-contact, nondestructive, fast and full-field measurement, digital holography has been widely applied in many fields, such as deformation and vibration analysis, particle characterization, refractive index measurement, and so on. In this paper, we present a method to measure the airflow field by use of digital holography. A small wind tunnel model made of acrylic glass is built to control the velocity and direction of airflow. Different shapes of samples such as aircraft wing and cylinder are placed in the wind tunnel model to produce different forms of flow field. With a Mach-Zehnder interferometer setup, a series of digital holograms carrying the information of airflow filed distributions in different states are recorded by CCD camera and corresponding holographic images are numerically reconstructed from the holograms by computer. Then we can conveniently obtain the velocity or pressure information of the airflow deduced from the quantitative phase information of holographic images and visually display the airflow filed and its evolution in the form of a movie. The theory and experiment results show that digital holography is a robust and feasible approach for real-time visualization and analysis of airflow field.

Di, Jianglei; Wu, Bingjing; Chen, Xin; Liu, Junjiang; Wang, Jun; Zhao, Jianlin

2013-04-01

103

Determining compressor-inlet airflow in the compact multimission aircraft propulsion simulators in wind-tunnel applications  

NASA Technical Reports Server (NTRS)

Test techniques are being developed to use the Compact Multimission Aircraft Propulsion Simulator (CMAPS) in wind-tunnel tests. The CMAPS allows simultaneous simulation of inlet and exhaust flow fields. Static tests have been conducted to acquire CMAPS performance data and to evaluate four methods of determining compressor inlet airflow during wind-tunnel tests. The first method measures airflow at the compressor face; the second measures airflow in the compressor discharge duct; the third deduces the compressor airflow from the calibrated nozzle, turbine supply, and turbine bleed airflows; and the fourth correlates compressor airflow with the mixer pressure. Test results and the advantages, disadvantages, and expected accuracy of each method are discussed.

Smith, S. C.

1983-01-01

104

Vapor-Generator Wand Helps To Reveal Airflow Patterns  

NASA Technical Reports Server (NTRS)

In vapor-generator wand, liquid propylene glycol flows into electrically heated stainless-steel tube. Liquid boils in heated tube, and emerging vapor forms dense, smoke-like fog used to make airflow patterns visible. Built in variety of sizes, suitable for uses ranging from tabletop demonstrations to research in wind tunnels. For best viewing, plume illuminated by bright, focused incandescent spotlight at right angle to viewing direction. Viewing further enhanced by coating walls of test chamber with flat, dark color to minimize reflections and increase contrast.

Robelen, David B.

1993-01-01

105

EFFECT OF AIRFLOW AND HEAT INPUT RATES ON DUCT EFFICIENCY.  

SciTech Connect

Reducing the airflow and heat input rates of a furnace that is connected to a duct system in thermal contact with unconditioned spaces can significantly reduce thermal distribution efficiency. This is a straightforward theoretical calculation based on the increased residence time of the air in the duct at the lower flow rate, which results in greater conduction losses. Experimental tests in an instrumented residential-size duct system have confirmed this prediction. Results are compared with the heat-loss algorithm in ASHRAE Standid 152P. The paper concludes with a discussion of possible remedies for this loss of efficiency in existing systems and optional design strategies in new construction.

ANDREWS,J.W.

2003-05-28

106

The Structure and Stability of Laminar Flames  

NASA Technical Reports Server (NTRS)

This review paper on the structure and stability of laminar flames considers such phenomena as heterogeneous mixtures, acoustic instabilities, flame balls and related phenomena, radiation effects, the iodate oxidation of arsenous acid and 'liquid flame fronts', approximate kinetic mechanisms and asymptotic approximations, and tribrachial or triple flames. The topics examined here indicate three themes that may play an important role in laminar flame theory in the coming years: microgravity experiments, kinetic modeling, and turbulence modeling. In the discussion of microgravity experiments it is pointed out that access to drop towers, the Space Shuttle and, in due course, the Space Station Freedom will encourage the development of experiments well designed to isolate the fundamental physics of combustion.

Buckmaster, John

1993-01-01

107

Insect contamination protection for laminar flow surfaces  

NASA Technical Reports Server (NTRS)

The ability of modern aircraft surfaces to achieve laminar flow was well-accepted in recent years. Obtaining the maximum benefit of laminar flow for aircraft drag reduction requires maintaining minimum leading-edge contamination. Previously proposed insect contamination prevention methods have proved impractical due to cost, weight, or inconvenience. Past work has shown that insects will not adhere to water-wetted surfaces, but the large volumes of water required for protection rendered such a system impractical. The results of a flight experiment conducted by NASA to evaluate the performance of a porous leading-edge fluid discharge ice protection system operated as an insect contamination protections system are presented. In addition, these flights explored the environmental and atmospheric conditions most suitable for insect accumulation.

Croom, Cynthia C.; Holmes, Bruce J.

1986-01-01

108

Compressible laminar flow in a channel  

NASA Astrophysics Data System (ADS)

Laminar flow of a compressible Newtonian fluid in a channel is analyzed. An analytic solution to the vorticity-stream function form of the hydrodynamics equations is found for weakly compressible flow using a regular perturbation method. In contrast with previous studies, the present analysis does not invoke the lubrication approximation and, consequently, predicts both a nonzero transverse velocity and a nonzero transverse pressure gradient. Predicted velocity and pressure fields from the perturbation solution are compared with previously published analytical and numerical solutions. Expressions for pressure drop are also given for compressible laminar flow in a channel that display significant deviations from the incompressible case. In addition, experimental data from the literature for the flow of gases in microchannels are analyzed and compared with predictions from the analytical solution. We find that a commonly used method for analyzing microchannel flow experiments obscures a rather simple dependence of pressure drop on the same dimensionless parameter used in the perturbation solution.

Venerus, D. C.; Bugajsky, D. J.

2010-04-01

109

Temperature distribution in a laminar circular jet  

Microsoft Academic Search

The effect of frictional heat on the temperature distribution in a laminar circular jet has been studied. It is found from\\u000a the analysis and the graphs that as the Prandtl number decreases from unity the overall temperature difference near the axis\\u000a of the jet increases but as we move away from the axis it goes on decreasing. The reverse phenomenon

S. S. Tak; J L Bansal

1979-01-01

110

Trans-Laminar-Reinforced (TLR) Composites  

NASA Technical Reports Server (NTRS)

A Trans-Laminar-Reinforced (TLR) composite is defined as composite laminate with up to five percent volume of fibrous reinforcement oriented in a 'trans-laminar' fashion in the through-thickness direction. The TLR can be continuous threads as in 'stitched laminates', or it can be discontinuous rods or pins as in 'Z-Fiber(TM) materials. It has been repeatedly documented in the literature that adding TLR to an otherwise two dimensional laminate results in the following advantages: substantially improved compression-after-impact response; considerably increased fracture toughness in mode 1 (double cantilever beam) and mode 2 (end notch flexure); and severely restricted size and growth of impact damage and edge delamination. TLR has also been used to eliminate catastrophic stiffener disbonding in stiffened structures. TLR directly supports the 'Achilles heel' of laminated composites, that is delamination. As little as one percent volume of TLR significantly alters the mechanical response of laminates. The objective of this work was to characterize the effects of TLR on the in-plane and inter-laminar mechanical response of undamaged composite laminates. Detailed finite element models of 'unit cells', or representative volumes, were used to study the effects of adding TLR on the elastic constants; the in-plane strength; and the initiation of delamination. Parameters investigated included TLR material, TLR volume fraction, TLR diameter, TLR through-thickness angle, ply stacking sequence, and the microstructural features of pure resin regions and curved in-plane fibers. The work was limited to the linear response of undamaged material with at least one ply interface. An inter-laminar dominated problem of practical interest, a flanged skin in bending, was also modeled.

Hinders, Mark; Dickinson, Larry

1997-01-01

111

Laminar Flow Control Flight Experiment Design  

E-print Network

at the surface of the Earth GIIB Gulfstream IIB aircraft GIII Gulfstream III aircraft h altitude H0 null hypothesis H1 alternate hypothesis 1 H2 alternate hypothesis 2 in inches IR infrared wavelength of light k DRE height K Kelvin xvii kg kilogram... reduction associated with a natural laminar flow wing glove at wing sweep, ? = 20?, Figure 8. Jetstar LFC aircraft [19] 16 as well as gathered data for computational validation [25]. Infrared (IR) cameras were used to measure transition location...

Tucker, Aaron 1975-

2012-11-29

112

Laminar Flow in the Ocean Ekman Layer  

NASA Astrophysics Data System (ADS)

INTRODUCTION THE EFFECT OF A STABLE DENSITY GRADIENT THE FATAL FLAW FLOW VISUALIZATION THE DISCOVERY OF LAMINAR FLOW FINE STRUCTURE WAVE-INDUCED SHEAR INSTABILITY BILLOW TURBULENCE REVERSE TRANSITION REVISED PARADIGM ONE-DIMENSIONAL MODELLING OF THE UPPER OCEAN DIURNAL VARIATION BUOYANT CONVECTION BILLOW TURBULENCE IN THE DIURNAL THERMOCLINE CONSEQUENCES FOR THE EKMAN CURRENT PROFILE SOLAR RADIATION APPLICATIONS Slippery Seas of Acapulco Pollution Afternoon Effect in Sonar Patchiness Fisheries Climate DISCUSSION CONCLUSION REFERENCES

Woods, J. T. H.

113

Investigation of non-uniform airflow signal oscillation during high frequency chest compression  

PubMed Central

Background High frequency chest compression (HFCC) is a useful and popular therapy for clearing bronchial airways of excessive or thicker mucus. Our observation of respiratory airflow of a subject during use of HFCC showed the airflow oscillation by HFCC was strongly influenced by the nonlinearity of the respiratory system. We used a computational model-based approach to analyse the respiratory airflow during use of HFCC. Methods The computational model, which is based on previous physiological studies and represented by an electrical circuit analogue, was used for simulation of in vivo protocol that shows the nonlinearity of the respiratory system. Besides, airflow was measured during use of HFCC. We compared the simulation results to either the measured data or the previous research, to understand and explain the observations. Results and discussion We could observe two important phenomena during respiration pertaining to the airflow signal oscillation generated by HFCC. The amplitudes of HFCC airflow signals varied depending on spontaneous airflow signals. We used the simulation results to investigate how the nonlinearity of airway resistance, lung capacitance, and inertance of air characterized the respiratory airflow. The simulation results indicated that lung capacitance or the inertance of air is also not a factor in the non-uniformity of HFCC airflow signals. Although not perfect, our circuit analogue model allows us to effectively simulate the nonlinear characteristics of the respiratory system. Conclusion We found that the amplitudes of HFCC airflow signals behave as a function of spontaneous airflow signals. This is due to the nonlinearity of the respiratory system, particularly variations in airway resistance. PMID:15904523

Sohn, Kiwon; Warwick, Warren J; Lee, Yong W; Lee, Jongwon; Holte, James E

2005-01-01

114

Laminar streak enhancement using streamwise grooves  

NASA Astrophysics Data System (ADS)

Laminar streak promotion in a flat plate boundary layer results in an increase of the stability of the Tollmien-Schlichting waves with respect to that of the 2D Blasius profile. This stabilization delays the laminar-turbulent transition, increasing the laminar phase of the flow. The stabilization effect is stronger for higher streak amplitudes, and therefore simple ways of generating high amplitude stable streaks are sought to be used as boundary layer flow control methods. In a recent experiment [Tallamelli & Franson,AIAA 2010-4291] high amplitude stable steady streaks have been produced using Miniature Vortex Generators (MGVs), where one array of MGVs is used to excite the streak and a second array is used downstream to enhance their amplitude. In this presentation we numerically explore the possibility of enhancing the streaks using a different passive mechanism: streamwise grooves carved in the plate. We will present some numerical simulations for different values of the spanwise period of the streaks and of the grooves, and we will show the combinations that provide maximum streak amplitude.

Martel, Carlos; Ángel Martín, Juan

2011-11-01

115

The minimum glottal airflow to initiate vocal fold oscillation.  

PubMed

Phonation threshold flow (PTF) is proposed as a new aerodynamic parameter of the speech production system in this study. PTF is defined as the minimum airflow that can initiate stable vocal fold vibration. Because the glottal airflow can be noninvasively measured, it is suggested that the aerodynamic parameter PTF may be more practical for clinical vocal disease assessment. In order to investigate the relationship between PTF and phonatory system properties, the stability of the body-cover vocal fold model was analyzed. The study has theoretically shown that PTF is a sensitive aerodynamic parameter dependent on tissue properties, glottal configuration, and vocal tract loading. It was predicted that PTF can be reduced by decreasing tissue viscosity, decreasing mucosal wave velocity, increasing vocal fold thickness, or decreasing prephonatory glottal area. Furthermore, it was predicted that a divergent glottis or low vocal tract resistance lead to a reduced PTF. Also discussed is the potential significance of PTF in investigating the energy distribution in a vocal fold vibration system and related clinical applications. PMID:17550186

Jiang, Jack J; Tao, Chao

2007-05-01

116

Airflow modelling over aeolian bedforms, Proctor Crater, Mars  

NASA Astrophysics Data System (ADS)

The presence of multiple dune forms inside Martian craters is evident on much of the recent HiRISE imagery available. Typically multiple length scales are present with progressively smaller bedform features superimposed on larger dunes, giving rise to complex but regular topographical patterns. There is a need to understand the airflow behaviour over these features to investigate if the formational pattern and orientation of the bedforms correspond to localised wind flow forcing. Using computational fluid dynamics (OpenFoam) we present preliminary findings within Mars' Proctor Crater, examining a dune area of 4.5km x 5.0km running with a computational cell resolution of 5m x 5m. A range of wind speed and directions are investigated and results are compared to bedform orientation and length scale. Superimposed over recent HiRISE imagery, results reveal a distinctive relationship between steered airflow and localised bedform orientation, mapping orthogonally onto the crestal ridges and dune troughs present. This work has important implications for the reconstruction of aeolian dunes within craters on Mars and can help lend further support to studies examining recent activity of Martian dune migration.

Jackson, D. W. T.; Smyth, T.; Bourke, M.

2012-04-01

117

Inspirational airflow patterns in deviated noses: a numerical study.  

PubMed

This study attempts to evaluate the effects of deviation of external nose to nasal airflow patterns. Four typical subjects were chosen for model reconstruction based on computed tomography images of undeviated, S-shaped deviated, C-shaped deviated and slanted deviated noses. To study the hypothetical influence of deviation of external nasal wall on nasal airflow (without internal blockage), the collapsed region along the turbinate was artificially reopened in all the three cases with deviated noses. Computational fluid dynamics simulations were carried out in models of undeviated, original deviated and reopened nasal cavities at both flow rates of 167 and 500 ml/s. The shape of the anterior nasal roof was found to be collapsed on one side of the nasal airways in all the deviated noses. High wall shear stress region was found around the collapsed anterior nasal roof. The nasal resistances in cavities with deviated noses were considerably larger than healthy nasal cavity. Patterns of path-line distribution and wall shear stress distribution were similar between original deviated and reopened models. In conclusion, the deviation of an external nose is associated with the collapse of one anterior nasal roof. The crooked external nose induced a larger nasal resistance compared to the undeviated case, while the internal blockage of the airway along the turbinates further increased it. PMID:22515677

Zhu, Jian Hua; Lee, Heow Pueh; Lim, Kian Meng; Lee, Shu Jin; San, Lynette Teo Li; Wang, De Yun

2013-01-01

118

Near surface airflow modelling over dunes in Proctor Crater, Mars  

NASA Astrophysics Data System (ADS)

Multiple dune forms inside Martian craters is evident on much of the recent Hi-Rise imagery available. Typically, multiple length scales are present with progressively smaller bedform features superimposed on larger dunes. This has produced complex but regular topographical aeolian-driven patterns. Understanding the airflow conditions over and around these features will help in our understanding of the formational patterns and orientation of the aeolian bedforms relative to localised wind flow forcing. Here we use computational fluid dynamics modelling and present preliminary findings within Mars' Proctor Crater over a dune area measuring 4.5km x 5.0km running with a computational cell resolution of 5m x 5m. A range of wind speed and directions are investigated and results are compared to bedform orientation, length scale and migration of ripples evident from recent HiRise imagery. Results reveal a distinctive relationship between steered airflow and localised bedform orientation, mapping orthogonally onto the crestal ridges present. This work has important implications for evolutionary reconstruction of aeolian dunes within craters on Mars and helps lend further support to studies examining recent activity of Martian dune migration.

Jackson, Derek; Bourke, Mary; Smyth, Thomas

2014-05-01

119

USABILITY EVALUATION OF A FLIGHT-DECK AIRFLOW HAZARD VISUALIZATION SYSTEM  

E-print Network

Abstract Many aircraft accidents each year are caused by encounters with unseen airflow hazards near goals: first, to assess the efficacy of presenting airflow data in flight; and second, to obtain expert the optimal way to provide critical safety information to the pilot, what level of detail to provide, whether

Hearst, Marti

120

Building ventilation : a pressure airflow model computer generation and elements of  

E-print Network

Building ventilation : a pressure airflow model computer generation and elements of validation H. Thus in tropical climates, natural ventilation affects essentially the inside comfort by favouring, the energetic aspect is the determining factor in these airflow transfers. In fact the importance of ventilation

Paris-Sud XI, Université de

121

Deposition rates of unattached and attached radon progeny in room with turbulent airflow and ventilation  

Microsoft Academic Search

In this paper deposition rate coefficients for unattached and attached radon progeny were estimated according to a particle deposition model for turbulent indoor airflow described by Zhao and Wu [2006. Modeling particle deposition from fully developed turbulent flow in ventilation duct. Atmos. Environ. 40, 457–466]. The parameter which characterizes turbulent indoor airflow in this model is friction velocity, u*. Indoor

N. Stevanovic; V. M. Markovic; D. Nikezic

2009-01-01

122

A computational study of the respiratory airflow characteristics in normal and obstructed human airways  

E-print Network

, bronchitis, and chronic obstructive pulmonary disease (COPD), are characterized by the obstruction of airflow lung diseases Peripheral airways Airflow pattern similarity measure Wall shear stress Computational fluid dynamics a b s t r a c t Obstructive lung diseases in the lower airways are a leading health

123

Studies on the Fluctuation Characteristics of Airflow in the Built Environment  

Microsoft Academic Search

The fluctuation characteristic of airflow is one of the important factors to influence the indoor thermal environment and human thermal comfort, which attracts researchers' interest in these years. This paper introduces the recent researches on the fluctuation characteristics of airflow conducted in Tsinghua University. Results show that there exist obvious differences and interesting connections between the fluctuation characteristics of natural

ZHU Yingxin; OUYANG Qin; JIANG Yi

124

Simulating Buoyancy-Driven Airflow in Buildings by1 Coarse-Grid Fast Fluid Dynamics2  

E-print Network

1 Simulating Buoyancy-Driven Airflow in Buildings by1 Coarse-Grid Fast Fluid Dynamics2 Mingang Jin1 the literature. The improved model has also been used to calculate the19 ventilation rate for buoyancy The integrated model was tested with buoyancy-driven airflow in buildings.28 The plume model can improve

Chen, Qingyan "Yan"

125

Flame Structure and Scalar Properties in Microgravity Laminar Fires  

NASA Technical Reports Server (NTRS)

Recent results from microgravity combustion experiments conducted in the Zero Gravity Facility (ZGF) 5.18 second drop tower are reported. Emission mid-infrared spectroscopy measurements have been completed to quantitatively determine the flame temperature, water and carbon dioxide vapor concentrations, radiative emissive power, and soot concentrations in a microgravity laminar ethylene/air flame. The ethylene/air laminar flame conditions are similar to previously reported experiments including the Flight Project, Laminar Soot Processes (LSP). Soot concentrations and gas temperatures are in reasonable agreement with similar results available in the literature. However, soot concentrations and flame structure dramatically change in long duration microgravity laminar diffusion flames as demonstrated in this paper.

Feikema, D. A.; Lim, J.; Sivathanu, Y.

2006-01-01

126

Research in Natural Laminar Flow and Laminar-Flow Control, part 2  

NASA Technical Reports Server (NTRS)

Part 2 of the Symposium proceedings includes papers addressing various topics in basic wind tunnel research/techniques and computational transitional research. Specific topics include: advanced measurement techniques; laminar flow control; Tollmien-Schlichting wave characteristics; boundary layer transition; flow visualization; wind tunnel tests; flight tests; boundary layer equations; swept wings; and skin friction.

Hefner, Jerry N. (compiler); Sabo, Frances E. (compiler)

1987-01-01

127

Precision temperature controlled filtered laminar air enclosure  

NASA Astrophysics Data System (ADS)

We demonstrate a novel temperature controlled filtered laminar air enclosure composed of primarily off-the-shelf components that can be applied to a broad class of systems to significantly enhance their performance. An air mixing method is employed to provide variable cooling of the incoming filtered air, providing a temperature stability of ± 0.02 °C within the enclosure. The method is inexpensive to implement, and is suitable for a wide range of temperature controlled enclosures, with dimensions in the approximate range from 1 m to 5 m, making it ideal for many scientific applications.

Dedman, C. J.; Henson, B. M.; Khakimov, R. I.; Truscott, A. G.; Dall, R. G.

2015-02-01

128

Velocity profiles in laminar diffusion flames  

NASA Technical Reports Server (NTRS)

Velocity profiles in vertical laminar diffusion flames were measured by using laser Doppler velocimetry (LDV). Four fuels were used: n-heptane, iso-octane, cyclohexane, and ethyl alcohol. The velocity profiles were similar for all the fuels, although there were some differences in the peak velocities. The data compared favorably with the theoretical velocity predictions. The differences could be attributed to errors in experimental positioning and in the prediction of temperature profiles. Error in the predicted temperature profiles are probably due to the difficulty in predicting the radiative heat losses from the flame.

Lyons, Valerie J.; Margle, Janice M.

1986-01-01

129

Class II (laminar flow) biological safety cabinet.  

PubMed

A microbiological survey of the effectiveness of class II (laminar flow) 'safety' cabinets found in the UK in the last six years is recorded. Only two of the nine units tested approached the containment of aerosols achieved by a good class I (exhaust protective) cabinet. The others were potentially hazardous if used with pathogenic material. The National Sanitation Foundation and the British Standards Institute have now laid down adequate specifications based on biological containment, and hopefully the conforming cabinets will be much better; even so, the purchase of a cabinet must be undertaken with care, and the cabinet requires frequent monitoring during use and after servicing. PMID:469008

Newsom, S W

1979-05-01

130

A dose-ranging study of phenylpropanolamine on nasal airflow.  

PubMed

A double-blind randomized placebo-controlled study comparing the effect of 2-dose levels of phenylpropanolamine (PPA) for acute rhinitis was performed in 180 outpatients. PPA was given in a fixed dose combination with paracetamol, chlorpheniramine and vitamin C. Two doses of each drug were given with a 4-h interval. Based on objective evaluation of nasal airflow using a Connell rhinometer, it was shown that PPA 25 mg was significantly more effective than the active placebo and PPA 15 mg. The decongestant effect of PPA 25 mg was markedly seen after 1 h, becoming maximal after 1.5 h, and was maintained for 2 h, after which the effect decreased until just before the second dose was given. The second dose gave a similar result as the first dose. PPA 15 mg was less effective and of shorter duration than the 25 mg dose, but gave sufficient improvement of nasal congestion. PMID:2387651

Darmansjah, I; Akib, H T; Setiawati, A; Muchtar, A; Rifki, N

1990-07-01

131

Thermal signatures help deduce evaporative fluxes into turbulent airflows  

NASA Astrophysics Data System (ADS)

Evaporative fluxes and energy balance of terrestrial surfaces are affected by interplay between water availability, energy input, and exchange across the air boundary layer. Commonly occurring turbulent airflows impose complex and highly dynamic boundary conditions that challenge prediction of surface evaporation rates. During stage-I evaporation where the vaporization plane is at the surface, intermittent turbulent interactions with the surface give rise to distinct thermal signatures that could be recorded using infrared thermography (IRT). The study links measured thermal signatures with spatio-temporal distribution of eddy-induced localized evaporation rates towards characterization of turbulent momentum field and estimation of overall evaporative fluxes. Results highlight potential of the approach for remote quantification of interactions between turbulent eddies and evaporating surfaces. Surface thermal inertia present a challenge to high resolution implementation, and strategies for overcoming these are presented including applications to plant canopies (low thermal inertia surfaces). Applications for larger scales will be discussed.

Haghighi, E.; Or, D.

2013-12-01

132

Respiratory symptoms and airflow limitation in asphalt workers  

PubMed Central

Aims: To assess the occurrence of respiratory symptoms and signs of airflow limitations in a group of asphalt workers. Methods: All 64 asphalt workers and a reference group of 195 outdoor construction workers from the same company participated in a cross-sectional study. Spirometric tests and a questionnaire on respiratory symptoms and smoking habits were administered. Respiratory symptoms and lung function were adjusted for age and smoking. Results: The FEV1/FVC% ratio was significantly lower in the asphalt workers than in the referents. Symptoms of eye irritation, chest tightness, shortness of breath on exertion, chest wheezing, physician diagnosed asthma, and chronic obstructive pulmonary disease (COPD) were all significantly more prevalent among the asphalt workers. Conclusion: In asphalt workers there is an increased risk of respiratory symptoms, lung function decline, and COPD compared to other construction workers. PMID:15031397

Randem, B; Ulvestad, B; Burstyn, I; Kongerud, J

2004-01-01

133

Uninstrumented assembly airflow testing in the Annular Flow Distribution facility  

SciTech Connect

During the Emergency Cooling System phase of a postulated large-break loss of coolant accident (ECS-LOCA), air enters the primary loop and is pumped down the reactor assemblies. One of the experiments performed to support the analysis of this accident was the Annular Flow Distribution (AFD) experiment, conducted in a facility built for this purpose at Babcock and Wilcox Alliance Research Center in Alliance, Ohio. As part of this experiment, a large body of airflow data were acquired in a prototypical mockup of the Mark 22 reactor assembly. This assembly was known as the AFD (or the I-AFD here) reference assembly. The I-AFD assembly was fully prototypical, having been manufactured in SRS`s production fabrication facility. Similar Mark 22 mockup assemblies were tested in several test facilities in the SRS Heat Transfer Laboratory (HTL). Discrepancies were found. The present report documents further work done to address the discrepancy in airflow measurements between the AFD facility and HTL facilities. The primary purpose of this report is to disseminate the data from the U-AFD test, and to compare these test results to the I-AFD data and the U-AT data. A summary table of the test data and the B&W data transmittal letter are included as an attachment to this report. The full data transmittal volume from B&W (including time plots of the various instruments) is included as an appendix to this report. These data are further analyzed by comparing them to two other HTL tests, namely, SPRIHTE 1 and the Single Assembly Test Stand (SATS).

Kielpinski, A.L.

1992-02-01

134

Fault tolerant attitude control for small unmanned aircraft systems equipped with an airflow sensor array.  

PubMed

Inspired by sensing strategies observed in birds and bats, a new attitude control concept of directly using real-time pressure and shear stresses has recently been studied. It was shown that with an array of onboard airflow sensors, small unmanned aircraft systems can promptly respond to airflow changes and improve flight performances. In this paper, a mapping function is proposed to compute aerodynamic moments from the real-time pressure and shear data in a practical and computationally tractable formulation. Since many microscale airflow sensors are embedded on the small unmanned aircraft system surface, it is highly possible that certain sensors may fail. Here, an adaptive control system is developed that is robust to sensor failure as well as other numerical mismatches in calculating real-time aerodynamic moments. The advantages of the proposed method are shown in the following simulation cases: (i) feedback pressure and wall shear data from a distributed array of 45 airflow sensors; (ii) 50% failure of the symmetrically distributed airflow sensor array; and (iii) failure of all the airflow sensors on one wing. It is shown that even if 50% of the airflow sensors have failures, the aircraft is still stable and able to track the attitude commands. PMID:25405953

Shen, H; Xu, Y; Dickinson, B T

2014-12-01

135

A Series of Laminar Jet Flame  

NASA Technical Reports Server (NTRS)

Study of the downlink data from the Laminar Soot Processes (LSP) experiment quickly resulted in discovery of a new mechanism of flame extinction caused by radiation of soot. Scientists found that the flames emit soot sooner than expected. These findings have direct impact on spacecraft fire safety, as well as the theories predicting the formation of soot -- which is a major factor as a pollutant and in the spread of unwanted fires. This sequence, using propane fuel, was taken STS-94, July 4 1997, MET:2/05:30 (approximate). LSP investigated fundamental questions regarding soot, a solid byproduct of the combustion of hydrocarbon fuels. The experiment was performed using a laminar jet diffusion flame, which is created by simply flowing fuel-like ethylene or propane -- through a nozzle and igniting it, much like a butane cigarette lighter. The LSP principal investigator was Gerard Faeth, University of Michigan, Arn Arbor. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). LSP results led to a reflight for extended investigations on the STS-107 research mission in January 2003. Advanced combustion experiments will be a part of investigations planned for the International Space Station. (249KB JPEG, 1350 x 1524 pixels; downlinked video, higher quality not available) The MPG from which this composite was made is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300185.html.

2003-01-01

136

Series of Laminar Soot Processes Experiment  

NASA Technical Reports Server (NTRS)

Study of the downlink data from the Laminar Soot Processes (LSP) experiment quickly resulted in discovery of a new mechanism of flame extinction caused by radiation of soot. Scientists found that the flames emit soot sooner than expected. These findings have direct impact on spacecraft fire safety, as well as the theories predicting the formation of soot -- which is a major factor as a pollutant and in the spread of unwanted fires. This sequence was taken July 15, 1997, MET:14/10:34 (approximate) and shows the ignition and extinction of this flame. LSP investigated fundamental questions regarding soot, a solid byproduct of the combustion of hydrocarbon fuels. The experiment was performed using a laminar jet diffusion flame, which is created by simply flowing fuel -- like ethylene or propane -- through a nozzle and igniting it, much like a butane cigarette lighter. The LSP principal investigator was Gerard Faeth, University of Michigan, Arn Arbor. The experiment was part of the space research investigations conducted during the Microgravity Science Laboratory-1R mission (STS-94, July 1-17 1997). LSP results led to a reflight for extended investigations on the STS-107 research mission in January 2003. Advanced combustion experiments will be a part of investigations planned for the International Space Station. (189KB JPEG, 1350 x 1517 pixels; downlinked video, higher quality not available) The MPG from which this composite was made is available at http://mix.msfc.nasa.gov/ABSTRACTS/MSFC-0300183.html.

2003-01-01

137

Modified laminar flow biological safety cabinet.  

PubMed

Tests are reported on a modified laminar flow biological safety cabinet in which the return air plenum that conducts air from the work area to the high efficiency particulate air filters is under negative pressure. Freon gas released inside the cabinet could not be detected outside by a freon gas detection method capable of detecting 10(-6) cc/s. When T3 bacteriophage was aerosolized 5 cm outside the front opening in 11 tests, no phage could be detected inside the cabinet with the motor-filter unit in operation. An average of 2.8 x 10(5) plaque-forming units (PFU)/ft(3) (ca. 0.028 m(3)) were detected with the motor-filter unit not in operation, a penetration of 0.0%. Aerosolization 5 cm inside the cabinet yielded an average of 10 PFU/ft(3) outside the cabinet with the motor-filter unit in operation and an average of 4.1 x 10(5) PFU/ft(3) with the motor-filter unit not in operation, a penetration of 0.002%. These values are the same order of effectiveness as the positive-pressure laminar flow biological safety cabinets previously tested. The advantages of the negative-pressure return plenum design include: (i) assurance that if cracks or leaks develop in the plenum it will not lead to discharge of contaminated air into the laboratory; and (ii) the price is lower due to reduced manufacturing costs. PMID:4420479

McGarrity, G J; Coriell, L L

1974-10-01

138

Data Visualization of Invisible Airflow Hazards During Helicopter Takeoff and Landing Operations  

NASA Technical Reports Server (NTRS)

Many aircraft accidents each year are caused by encounters with unseen airflow hazards near the ground such as vortices, downdrafts, wind shear, microbursts, or other turbulence. While such hazards frequently pose problems to fixed-wing airplanes, they are especially dangerous to helicopters, which often have to operate in confined spaces and under operationally stressful conditions. We are developing flight-deck visualizations of airflow hazards during helicopter takeoff and landing operations, and are evaluating their effectiveness with usability studies. Our hope is.that this work will lead to the production of an airflow hazard detection system for pilots that will save lives.

Aragon, Cecilia R.

2004-01-01

139

Laminar Premixed and Diffusion Flames (Ground-Based Study)  

NASA Technical Reports Server (NTRS)

Ground-based studies of soot processes in laminar flames proceeded in two phases, considering laminar premixed flames and laminar diffusion flames, in turn. The test arrangement for laminar premixed flames involved round flat flame burners directed vertically upward at atmospheric pressure. The test arrangement for laminar jet diffusion flames involved a round fuel port directed vertically upward with various hydrocarbon fuels burning at atmospheric pressure in air. In both cases, coflow was used to prevent flame oscillations and measurements were limited to the flame axes. The measurements were sufficient to resolve soot nucleation, growth and oxidation rates, as well as the properties of the environment needed to evaluate mechanisms of these processes. The experimental methods used were also designed to maintain capabilities for experimental methods used in corresponding space-based experiments. This section of the report will be limited to consideration of flame structure for both premixed and diffusion flames.

Dai, Z.; El-Leathy, A. M.; Lin, K.-C.; Sunderland, P. B.; Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

2000-01-01

140

42 CFR 84.1149 - Airflow resistance tests; all dust, fume, and mist respirators; minimum requirements.  

Code of Federal Regulations, 2011 CFR

... Dust, Fume, and Mist; Pesticide; Paint Spray; Powered Air-Purifying High Efficiency Respirators and Combination Gas Masks § 84.1149 Airflow resistance tests; all dust, fume, and mist respirators; minimum requirements. (a)...

2011-10-01

141

Building ventilation: A pressure airflow model computer generation and elements of validation  

E-print Network

The calculation of airflows is of great importance for detailed building thermal simulation computer codes, these airflows most frequently constituting an important thermal coupling between the building and the outside on one hand, and the different thermal zones on the other. The driving effects of air movement, which are the wind and the thermal buoyancy, are briefly outlined and we look closely at their coupling in the case of buildings, by exploring the difficulties associated with large openings. Some numerical problems tied to the resolving of the non-linear system established are also covered. Part of a detailled simulation software (CODYRUN), the numerical implementation of this airflow model is explained, insisting on data organization and processing allowing the calculation of the airflows. Comparisons are then made between the model results and in one hand analytical expressions and in another and experimental measurements in case of a collective dwelling.

Boyer, H; Adelard, L; Mara, T A

2012-01-01

142

Coupling of a multizone airflow simulation program with computational fluid dynamics for indoor environmental analysis  

E-print Network

Current design of building indoor environment comprises macroscopIC approaches, such as CONT AM multizone airflow analysis tool, and microscopic approaches that apply Computational Fluid Dynamics (CFD). Each has certain ...

Gao, Yang, 1974-

2002-01-01

143

Laminar flow control perforated wing panel development  

NASA Technical Reports Server (NTRS)

Many structural concepts for a wing leading edge laminar flow control hybrid panel were analytically investigated. After many small, medium, and large tests, the selected design was verified. New analytic methods were developed to combine porous titanium sheet bonded to a substructure of fiberglass and carbon/epoxy cloth. At -65 and +160 F test conditions, the critical bond of the porous titanium to the composite failed at lower than anticipated test loads. New cure cycles, design improvements, and test improvements significantly improved the strength and reduced the deflections from thermal and lateral loadings. The wave tolerance limits for turbulence were not exceeded. Consideration of the beam column midbay deflections from the combinations of the axial and lateral loadings and thermal bowing at -65 F, room temperature, and +160 F were included. Many lap shear tests were performed at several cure cycles. Results indicate that sufficient verification was obtained to fabricate a demonstration vehicle.

Fischler, J. E.

1986-01-01

144

Thermohydrodynamic analysis for laminar lubricating films  

NASA Technical Reports Server (NTRS)

A Galerkin-type analysis to include thermal effects in laminar lubricating films was performed. The lubricant properties were assumed constant except for a temperature-dependent Newtonian viscosity. The cross-film temperature profile is established by collocation at the film boundaries and two interior Lobatto points. The interior temperatures are determined by requiring that the zeroth and first moment of the energy equation be satisfied across the film. The fluidity is forced to conform to a third--degree polynomial appropriate to the Lobatto-point temperatures. Preliminary indications are that the use of just two such sampling points enables satisfactory prediction of bearing performance even in the presence of substantial viscosity variation.

Elrod, H. G.; Brewe, D. E.

1986-01-01

145

On the combustion of a laminar spray  

NASA Technical Reports Server (NTRS)

A spray combustor, with flow velocities in the laminar range, exhibits a unique operating mode where large amplitude, self-induced oscillations of the flame shape occur. The phenomenon, not previously encountered, only occurs when fuel is supplied in the form of fine liquid droplets and does not occur when fuel is supplied in gaseous form. Several flow mechanisms are coupled in such a fashion as to trigger and maintain the oscillatory motion of the flame. These mechanisms include heat transfer and evaporation processes, dynamics of two-phase flows, and effects of gravity (buoyancy forces). An interface volume, lying above the fuel nozzle and below the flame was found to be the most susceptible to gravity effects and postulated to be responsible for inducing the oscillatory motion. Heptane fuel was used in the majority of the tests. Tests performed with iso-octane also showed similar results.

Levy, Yeshayahou; Bulzan, Daniel L.

1993-01-01

146

Beta adrenoceptor binding and induced relaxation in airway smooth muscle from patients with chronic airflow obstruction.  

PubMed Central

Beta adrenoceptor function in central airway smooth muscle of patients with chronic airflow obstruction was investigated by radioligand binding studies and isoprenaline relaxation experiments. Receptor characteristics were determined in tracheal smooth muscle preparations obtained at necropsy from 12 patients and in bronchial tissue obtained at thoracototomy from 21 patients with chronic airflow obstruction. Receptor characteristics were compared with those obtained in airway tissue preparations from 65 control subjects without chronic airflow obstruction. The number of beta adrenoceptors, their binding affinity for the radioligand [125I]-(-)-cyanopindolol, and the tissue binding characteristics of isoprenaline were similar in tissue from patients with chronic airflow obstruction and from control subjects. Isoprenaline induced relaxation of tracheal smooth muscle without precontraction by methacholine showed slightly (though not significantly) less sensitivity to isoprenaline in patients with chronic airflow obstruction than in control subjects (mean (SEM) pD2--the negative logarithm of the concentration producing 50% relaxation--6.32 (0.16) v 6.62 (0.15)). The same pattern of pD2 values was found in segmental bronchial strips without precontraction by methacholine (chronic airflow obstruction 6.55 (0.27), control 7.14 (0.12)). Isoprenaline relaxation in segmental bronchial strips when contracted maximally was significantly less in the patients with airflow obstruction than in the control subjects (pD2 value 5.99 (0.18) v 6.45 (0.07)). These results suggest that beta adrenoceptors in airway smooth muscle of patients with chronic airflow obstruction are not abnormal in number or in binding affinity but that there is less effective coupling between components of the relaxant system distal to the beta adrenoceptor. The possibility that the reduced isoprenaline sensitivity is a consequence of previous bronchodilator treatment cannot be excluded. PMID:2538944

van Koppen, C J; de Miranda, J F; Beld, A J; van Herwaarden, C L; Lammers, J W; van Ginneken, C A

1989-01-01

147

Topographic Steering of Alongshore Airflow over a Vegetated Foredune: Greenwich Dunes, Prince Edward Island, Canada  

Microsoft Academic Search

WALKER, I.J.; HESP, P.A.; DAVIDSON-ARNOTT, R.G.D., and OLLERHEAD, J., 2006. Topographic steering of along- shore airflow over a vegetated foredune: Greenwich Dunes, Prince Edward Island, Canada. Journal of Coastal Re- search, 22(5), 1278-1291. West Palm Beach (Florida), ISSN 0749-0208. High-frequency measurements of airflow from ultrasonic anemometers and time-averaged cup anemometer profiles were taken during an oblique alongshore sand-transporting event (6.7

Ian J. Walker; Patrick A. Hesp; Robin G. D. Davidson-Arnott; Jeff Ollerhead

2006-01-01

148

An instrumented sample holder for time-lapse microtomography measurements of snow under advective airflow  

NASA Astrophysics Data System (ADS)

An instrumented sample holder was developed for time-lapse microtomography of snow samples to enable in situ nondestructive spatial and temporal measurements under controlled advective airflows, temperature gradients, and air humidities. The design was aided by computational fluid dynamics simulations to evaluate the airflow uniformity across the snow sample. Morphological and mass transport properties were evaluated during a 4-day test run. This instrument allows the experimental characterization of metamorphism of snow undergoing structural changes with time.

Ebner, P. P.; Grimm, S. A.; Schneebeli, M.; Steinfeld, A.

2014-09-01

149

Numerical simulations of airflow and droplet transport in a wave-plate mist eliminator  

Microsoft Academic Search

In this paper, the droplet transport and deposition in the turbulent airflow inside a wave-plate mist eliminator was studied using an Eulerian–Lagrangian computational method. The Reynolds Stress Transport Model (RSTM) with standard wall functions and with enhanced wall treatment was used for simulating the airflow field. A computer code for solving the Reynolds-averaged Navier–Stokes (RANS) equations in conjunction with the

R. Rafee; H. Rahimzadeh; G. Ahmadi

2010-01-01

150

F-111 TACT natural laminar flow glove flight results  

NASA Technical Reports Server (NTRS)

Improvements in cruise efficiency on the order of 15 to 40% are obtained by increasing the extent of laminar flow over lifting surfaces. Two methods of achieving laminar flow are being considered, natural laminar flow and laminar flow control. Natural laminar flow (NLF) relies primarily on airfoil shape while laminar flow control involves boundary layer suction or blowing with mechanical devices. The extent of natural laminar flow that could be achieved with consistency in a real flight environment at chord Reynolds numbers in the range of 30 x 10(6) power was evaluated. Nineteen flights were conducted on the F-111 TACT airplane having a NLF airfoil glove section. The section consists of a supercritical airfoil providing favorable pressure gradients over extensive portions of the upper and lower surfaces of the wing. Boundary layer measurements were obtained over a range of wing leading edge sweep angles at Mach numbers from 0.80 to 0.85. Data were obtained for natural transition and for a range of forced transition locations over the test airfoil.

Montoya, L. C.; Steers, L. L.; Trujillo, B.

1981-01-01

151

Three-Dimensional Engineered High Fidelity Normal Human Lung Tissue-Like Assemblies (TLA) as Targets for Human Respiratory Virus Infections  

NASA Technical Reports Server (NTRS)

Unlike traditional two-dimensional (2D) cell cultures, three-dimensional (3D) tissue-like assemblies (TLA) (Goodwin et aI, 1992, 1993, 2000 and Nickerson et aI. , 2001,2002) offer high organ fidelity with the potential to emulate the infective dynamics of viruses and bacteria in vivo. Thus, utilizing NASA micro gravity Rotating Wall Vessel (RWV) technology, in vitro human broncho-epithelial (HBE) TLAs were engineered to mimic in vivo tissue for study of human respiratory viruses. These 3D HBE TLAs were propagated from a human broncho-tracheal cell line with a mesenchymal component (HBTC) as the foundation matrix and either an adult human broncho-epithelial cell (BEAS-2B) or human neonatal epithelial cell (16HBE140-) as the overlying element. Resulting TLAs share several characteristic features with in vivo human respiratory epithelium including tight junctions, desmosomes and cilia (SEM, TEM). The presence of epithelium and specific lung epithelium markers furthers the contention that these HBE cells differentiate into TLAs paralleling in vivo tissues. A time course of infection of these 3D HBE TLAs with human respiratory syncytial virus (hRSV) wild type A2 strain, indicates that virus replication and virus budding are supported and manifested by increasing virus titer and detection of membrane-bound F and G glycoproteins. Infected 3D HBE TLAs remain intact for up to 12 days compared to infected 2D cultures that are destroyed in 2-3 days. Infected cells show an increased vacuolation and cellular destruction (by transmission electron microscopy) by day 9; whereas, uninfected cells remain robust and morphologically intact. Therefore, the 3D HBE TLAs mimic aspects of human respiratory epithelium providing a unique opportunity to analyze, for the first time, simulated in vivo viral infection independent of host immune response.

Goodwin, T. J.; Deatly, A. M.; Suderman, M. T.; Lin, Y.-H.; Chen, W.; Gupta, C. K.; Randolph, V. B.; Udem, S. A.

2003-01-01

152

Simultaneous detection of particles and airflow with a MEMS piezoresistive cantilever  

NASA Astrophysics Data System (ADS)

This paper describes a particle and airflow sensor using a MEMS piezoresistive cantilever with the dimensions of 250 µm × 200 µm × 0.29 µm. The sensor structure is simple and detects both the airflow velocity and particle collisions by measuring the fractional resistance change due to the cantilever bending. The signals of the airflow velocity and particle collisions can be simultaneously detected by distinguishing continuous and pulse responses. The sensitivity to the airflow velocity was 1.2 × 10-3 (m/s)-1 from 0 to 2.5 m s-1. When a particle of 35 µm diameter (Lycopodium) collided with the cantilever surface, the fractional resistance change varied with the collision. After the collision, reverberation occurred at 3 kHz, which was the same as the resonance frequency of the cantilever. The magnitude of the fractional resistance changes due to particle collision was proportional to the airflow velocity. The sensitivity to particle collision was 2.0 × 10-3 (m/s)-1 when the airflow velocity varied between 0 and 2.5 m s-1.

Takahashi, Hidetoshi; Kan, Tetsuo; Matsumoto, Kiyoshi; Shimoyama, Isao

2013-02-01

153

Investigation on side-spray fluidized bed granulation with swirling airflow.  

PubMed

Top-spray fluidized bed granulation with axial fluidization airflow from the bottom of the granulator is well-established in the pharmaceutical industry. The application of swirling airflow for fluidized bed granulation was more recently introduced. This study examined the effects of various process parameters on the granules produced by side-spray fluidized bed with swirling airflow using the central composite and Box-Behnken design of experiment. Influence of the amount of binder solution, spray rate, and distance between spray nozzle and powder bed were initially studied to establish operationally viable values for these parameters. This was followed by an in-depth investigation on the effects of inlet airflow rate, atomizing air pressure and distance between spray nozzle and powder bed on granule properties. It was found that the amount of binder solution had a positive correlation with granule size and percentage of lumps but a negative correlation with size distribution and Hausner ratio of the granules. Binder solution spray rate was also found to affect the granules size. High drug content uniformity was observed in all the batches of granules produced. Both inlet airflow rate and atomizing air pressure were found to correlate negatively with granule size and percentage of lumps but correlate positively with the size distribution of the granule produced. Percentage of fines was found to be significantly affected by inlet airflow rate. Distance between spray nozzle and powder bed generally affected the percentage of lumps. PMID:23263750

Wong, Poh Mun; Chan, Lai Wah; Heng, Paul Wan Sia

2013-03-01

154

Cigarette smoke potentiates asbestos-induced airflow abnormalities  

SciTech Connect

It has been suggested that exposure to both asbestos and cigarette smoke can produce worse parenchymal lung disease than exposure to asbestos alone. Using a guinea pig model of asbestos administration that produces primarily airway disease and associated airflow abnormalities, we showed previously that the combination of asbestos and smoke acts synergistically to produce more marked increases in tissue collagen, fibrosis of airway walls, and early interstitial fibrosis than are seen with asbestos alone. To investigate the functional effects of these morphological and biochemical abnormalities, pulmonary function tests for volumes and flows, including lung volumes, pressure-volume curves, and flow-volume curves, were performed. By themselves, both smoke and asbestos produced increases in total lung capacity (TLC), residual volume (RV), and functional residual capacity (FRC); the two agents together made all these changes worse than either one alone. Both smoking and asbestos moved the pressure-volume curve upward, and the effects of the two agents together were again greater than either alone. Similarly, both smoke and asbestos decreased flows, and the two agents produced more severe impairment than either one by itself. The changes in volumes, pressure-volume curve, and flows correlated with both increased thickness of small airway walls and increases in airspace size. These observations indicate that, at least in this guinea pig model, cigarette smoke can potentiate the functional consequences of asbestos exposure.

Wright, J.L.; Tron, V.; Wiggs, B.; Churg, A.

1988-01-01

155

Evaluation of airflow patterns following procedures established by NUREG-1400  

SciTech Connect

The U.S. Nuclear Regulatory Commission's NUREG-1400 addresses many aspects of air sampling in the work place. Here, we present two detailed examples of the implementation of qualitative air flow studies at different scales using guidelines established by NUREG-1400. In one test, smoke was used to evaluate the airflow patterns within the transfer area of the 105 KE Basin, located on the Hanford Site, Richland, Washington. The purpose of the study was to determine appropriate locations for air monitoring equipment in support of sludge water pumping activities. The study revealed a stagnant layer of the air within the transfer area that made predicting movement of contamination within the transfer area difficult. Without conducting an air flow study, the stagnant layer would not have been identified, and could have resulted in locating samplers at inappropriate locations. In a second test, smoke was used to verify the effectiveness of an air space barrier curtain. The results showed that the curtain adequately separated the two air spaces. The methodology employed in each test provided sound, easy to interpret information that satisfied the requirements of each test.

Fritz, Brad G.; Khan, Fenton; Mendoza, Donaldo P.

2006-07-26

156

Modeling and fabrication of a planar thin film airflow sensor  

NASA Astrophysics Data System (ADS)

A thin film airflow transducer based on the hot wire anemometer principle was designed using current MEMS modelling & simulation software. Flow sensors are commonly implemented with thermal isolation of the sensor from the bulk substrate mass using methods such as reverse side etching or sacrificial layers, however this paper will present a sensor relying on thermal insulation only. This insulation may be provided by layers of material exhibiting relatively poor thermal conduction characteristics such as silicon dioxide or polyimide, giving rise to a number of advantages such as removing the process of reverse side etching. Limiting fabrication to use of simple processes such as photolithography and sputtering/evaporative deposition also simplifies this design and assists in greatly increasing the compatibility with standard CMOS fabrication processes and materials. A combination of both theoretical computer modelling and physical fabrication and testing has been the approach to this research. Preliminary testing of this design has demonstrated small yet measurable temperature gradients across the device surface during steady state operation. The novel approach to this device is the investigation of pulsed operation, effectively a transient analysis that allows the thermal conduction effects of the bulk mass to be significantly reduced, leading to a significant increase of both efficiency and response time. Electro-thermo-mechanical and computational fluid dynamic analysis of the structure successfully model the thermal conduction, radiation and forced convection effects of the device during and after ohmic heating of the sensor's heating element.

Adamec, Richard J.; Tanner, Philip G.; Thiel, David V.

2001-11-01

157

A miniature airflow energy harvester from piezoelectric materials  

NASA Astrophysics Data System (ADS)

This paper describes design, simulation, fabrication, and testing of a miniature wind energy harvester based on a flapping cantilevered piezoelectric beam. The wind generator is based on oscillations of a cantilever that faces the direction of the airflow. The oscillation is amplified by interactions between an aerofoil attached on the cantilever and a bluff body placed in front of the aerofoil. A piezoelectric transducer with screen printed PZT materials is used to extract electrical energy. To achieve the optimum design of the harvester, both computational simulations and experiments have been carried out to investigate the structure. A prototype of the wind harvester, with the volume of 37.5 cm3 in total, was fabricated by thick-film screen printing technique. Wind tunnel test results are presented to determine the optimum structure and to characterize the performance of the harvester. The optimized device finally achieved a working wind speed range from 1.5 m/s to 8 m/s. The power output was ranging from 0.1 to 0.86 ?W and the open-circuit output voltage was from 0.5 V to 1.32 V.

Sun, H.; Zhu, D.; White, N. M.; Beeby, S. P.

2013-12-01

158

Inductively coupled plasma torch with laminar flow cooling  

DOEpatents

An improved inductively coupled gas plasma torch. The torch includes inner and outer quartz sleeves and tubular insert snugly fitted between the sleeves. The insert includes outwardly opening longitudinal channels. Gas flowing through the channels of the insert emerges in a laminar flow along the inside surface of the outer sleeve, in the zone of plasma heating. The laminar flow cools the outer sleeve and enables the torch to operate at lower electrical power and gas consumption levels additionally, the laminar flow reduces noise levels in spectroscopic measurements of the gaseous plasma.

Rayson, Gary D. (Las Cruces, NM); Shen, Yang (Las Cruces, NM)

1991-04-30

159

Laminar Flow Control Leading Edge Systems in Simulated Airline Service  

NASA Technical Reports Server (NTRS)

Achieving laminar flow on the wings of a commercial transport involves difficult problems associated with the wing leading edge. The NASA Leading Edge Flight Test Program has made major progress toward the solution of these problems. The effectiveness and practicality of candidate laminar flow leading edge systems were proven under representative airline service conditions. This was accomplished in a series of simulated airline service flights by modifying a JetStar aircraft with laminar flow leading edge systems and operating it out of three commercial airports in the United States. The aircraft was operated as an airliner would under actual air traffic conditions, in bad weather, and in insect infested environments.

Wagner, R. D.; Maddalon, D. V.; Fisher, D. F.

1988-01-01

160

Selected experiments in laminar flow: An annotated bibliography  

NASA Technical Reports Server (NTRS)

Since the 1930s, there have been attempts to reduce drag on airplanes by delaying laminar to turbulent boundary layer transition. Experiments conducted during the 1940's, while successful in delaying transition, were discouraging because of the careful surface preparation necessary to meet roughness and waviness requirements. The resulting lull in research lasted nearly 30 years. By the late 1970s, airframe construction techniques had advanced sufficiently that the high surface quality required for natural laminar flow (NLF) and laminar flow control (LFC) appeared possible on production aircraft. As a result, NLF and LFC research became widespread. This report is an overview of that research. The experiments summarized herein were selected for their applicability to small transonic aircraft. Both flight and wind tunnel tests are included. The description of each experiment is followed by corresponding references. Part One summarizes NLF experiments; Part Two deals with LFC and hybrid laminar flow control (HLFC) experiments.

Drake, Aaron; Kennelly, Robert A., Jr.

1992-01-01

161

The effects of surface instabilities on laminar film condensation  

E-print Network

Heat transfer rates for laminar film condensation of Freon-1l3 were measured on the underside of horizontal surfaces, inclined surfaces, and vertical surfaces. Several distinct regimes of flow were observed. On the underside ...

Gerstmann, Joseph

1965-01-01

162

Conceptual design for a laminar-flying-wing aircraft  

E-print Network

Conceptual Design for a Laminar-Flying-Wing Aircraft Tariq Issam Saeed Trinity Hall University of Cambridge A thesis submitted for the degree of Doctor of Philosophy February 2012 Declaration Described in this dissertation is worked performed...

Saeed, Tariq Issam

2012-06-12

163

Design of fuselage shapes for natural laminar flow  

NASA Technical Reports Server (NTRS)

Recent technological advances in airplane construction techniques and materials allow for the production of aerodynamic surfaces without significant waviness and roughness, permitting long runs of natural laminar flow (NLF). The present research effort seeks to refine and validate computational design tools for use in the design of axisymmetric and nonaxisymmetric natural-laminar-flow bodies. The principal task of the investigation involves fuselage body shaping using a computational design procedure. Analytical methods were refined and exploratory calculations conducted to predict laminar boundary-layer on selected body shapes. Using a low-order surface-singularity aerodynamic analysis program, pressure distribution, boundary-layer development, transition location and drag coefficient have been obtained for a number of body shapes including a representative business-aircraft fuselage. Extensive runs of laminar flow were predicted in regions of favorable pressure gradient on smooth body surfaces. A computational design procedure was developed to obtain a body shape with minimum drag having large extent of NLF.

Dodbele, S. S.; Vandam, C. P.; Vijgen, P. M. H. W.

1986-01-01

164

Studies in Counterflow Laminar Flame Theory  

NASA Astrophysics Data System (ADS)

This dissertation describes asymptotic analyses of counterflow laminar diffusion and premixed flames with density changes and swirl taken into account. The employed asymptotic methods are based on large Reynolds numbers and Zel'dovich numbers to resolve thin viscous and reactive layers. Three different types of laminar flames in counterflow are analyzed to show that the density changes associated with heat release result in significant displacement effects and thus in significant alterations of the rate of strain attributed to the flow external to the flame. The analysis involves the classical sequence of calculating the first order inviscid flow which yields the standard expression for the rate of strain, the first order inner flow describing the structure of the flame and the displacement of the flame on the inviscid flow and finally the second order outer flow yielding the correction to the rate of strain. Comparison is made with some experimental results to demonstrate the significant alterations to that rate by displacement effects. A parametric analysis is performed of the counterflow mixing of two gas streams having different temperatures, with density changes taken into account. Numerical integrations of the similarity equations for counterflow mixing are completed to provide velocity, temperature and mixture -fraction fields. Results are applicable to obtain the better prediction of the structure and extinction of counterflow diffusion flames. The characteristics of isenthalpic planar premixed flames in counterflowing streams involving either corotating or counterrotating swirl of large magnitudes are analyzed. The method of activation energy asymptotics is applied to a one step Arrhenius reaction with small departures from unity Lewis numbers. Density changes resulting from heat release are fully taken into account. High swirl is shown to lead to three stagnation points and regions of radial inflow in agreement with experiment. It is shown that the character of the viscous layers containing the flames and their extinction behavior are significantly influenced by swirl for strong rate of swirl. The resonances found in an earlier inviscid calculation are shown not to be realizable and the reversal of the lean flammability limit with rotation found experimentally is explained.

Kim, Jong Soo

165

Ignition in laminar and turbulent nonpremixed counterflow  

NASA Astrophysics Data System (ADS)

Investigations into nonpremixed ignition were conducted to examine the influence of complex chemistry and flow turbulence as found in practical combustion systems. The counterflow configuration, where a hot air jet ignited a cold (298K) fuel jet, was adopted in experiments and calculations. The study of the ignition of large alkane hydrocarbons focused on the effects of fuel structure by investigating the reference fuels n-heptane and iso-octane. The ignition response of these fuels was similar to smaller fuels with similar molecular structures. This conclusion was reinforced by showing that the ignition temperature became nearly insensitive to fuel molecule size above C4, but continued to depend on whether the structure was linear or branched. The effects of turbulence were studied by adding perforated plates to the burner to generate controlled levels of turbulence. This configuration was examined in detail experimentally and computationally without reaction, and subsequently the effects of turbulence on ignition were studied with hydrogen as the fuel. The results indicated that at low turbulence intensities, ignition is enhanced relative to laminar ignition, but as the turbulence intensity increases the ignition temperature also increases, demonstrating that optimal conditions for ignition exist at low turbulence intensities. At high pressures, where HO2 chemistry is important, all turbulent ignition temperatures were higher than laminar ones, and the increasing temperature trend with turbulence intensity was still observed. At low fuel concentrations, a different ignition mode was observed where the transition from a weakly reacting state to a flame occurred over a range of temperatures where the flame was repeatedly ignited and extinguished. Turbulent ignition was modeled by solving a joint scalar PDF equation using a Monte Carlo technique. The absence of significant heat release prior to ignition enabled the use of a frozen flow solution, solved separately, in the scalar calculation. The results did not reproduce the qualitative trends noted in the experiments and the influence of turbulence intensity was not apparent in the calculated results. These discrepancies were attributed to shortcomings in the molecular mixing models in low turbulent Reynolds number flows and where reaction rates are much lower than in a flame.

Blouch, John Dewey

2002-01-01

166

Natural laminar flow airfoil analysis and trade studies  

NASA Technical Reports Server (NTRS)

An analysis of an airfoil for a large commercial transport cruising at Mach 0.8 and the use of advanced computer techniques to perform the analysis are described. Incorporation of the airfoil into a natural laminar flow transport configuration is addressed and a comparison of fuel requirements and operating costs between the natural laminar flow transport and an equivalent turbulent flow transport is addressed.

1979-01-01

167

The laminar axisymmetric wake for power-law fluids  

Microsoft Academic Search

Summary An analytic solution is given for the asymptotic structure of the axisymmetric laminar wake of a power-law fluid valid for rheological indicesn>1\\/3. For dilatant fluids (n>1) the lateral extent of the wake is finite, a feature not found in Newtonian fluid flows. Velocity profiles are compared with previously published results for two-dimensional laminar wakes of power-law fluids at selected

P. D. Weidman; C. W. Van Atta

2001-01-01

168

Laminar profiles of functional activity in the human brain  

Microsoft Academic Search

Functional magnetic resonance imaging (fMRI) data were obtained in human visual cortex using sub-millimeter voxels at a field strength of 3 T. Reliable functional signals were largely confined to the gray matter and these responses measure the retinotopic organization of visual cortex. Functional signals were further characterized with respect to their laminar position within the cortical gray matter. The laminar response

David Ress; Gary H. Glover; Junjie Liu; Brian Wandell

2007-01-01

169

Coupled thermal-fluid-structure behavior of airflow over target irradiated by high-power laser  

NASA Astrophysics Data System (ADS)

In this paper, a coupled thermal-fluid-structure numerical model is presented to investigate interactive effects of supersonic airflow, high power laser and metallic target. The numerical model is validated by experiments recently carried out by Lawrence Livermore National Laboratory. The numerical simulation also verified some experimental observations, which show that the convective heat transfer effects of airflow and the aerodynamic pressure play important roles to the damage behavior of laser irradiated target. The convective heat transfer of airflow reduces the temperature of laser irradiated area therefore delays the time reaching damage. When a thin-walled metallic panel is heated up to a high temperature below the melting point, it is softened and the strength nearly vanishes, the aerodynamic pressure becomes a dominant factor that controls the damage pattern even when it is in a low magnitude. The effects of airflow velocity and laser power on the damage behavior of irradiated metallic target are investigated with the aid of the coupled thermal-fluid-structure numerical model, where critical irradiation times to reach the yield failure t yield and melting failure t yield are the main concern. Results show that, when the incidence laser power increases from 500 W/cm2 to 5000 W/cm2, significant drop in failure times are found as the incidence laser power increases. When the Mach number of airflow increases from 1.2 to 4.0 at a given incident laser power, a critical airflow velocity is found for the irradiation time to reach the yield strength and melting point, i.e., the maximum irradiation time to reach failure is found at the Mach 1.8~2.0. The competition of aerodynamic heating before the laser is switch on and airflow cooling after the target is heated up accounts for effects.

Huang, Yihui; Song, Hongwei; Huang, Chenguang

2013-05-01

170

Application of natural laminar flow to a supersonic transport concept  

NASA Technical Reports Server (NTRS)

Results are presented of a preliminary investigation into an application of supersonic natural laminar flow (NLF) technology for a high speed civil transport (HSCT) configuration. This study focuses on natural laminar flow without regard to suction devices which are required for laminar flow control (LFC) or hybrid laminar flow control (HLFC). An HSCT design is presented with a 70 deg inboard leading-edge sweep and a 20 deg leading-edge outboard crank to obtain NLF over the outboard crank section. This configuration takes advantage of improved subsonic performance and NLF on the low-sweep portion of the wing while minimizing the wave drag and induced drag penalties associated with low-sweep supersonic cruise aircraft. In order to assess the benefits of increasing natural laminar flow wetted area, the outboard low-sweep wing area is parametrically increased. Using a range of supersonic natural laminar flow transition Reynolds numbers, these aircraft are then optimized and sized for minimum take-off gross weight (TOGW) subject to mission constraints. Results from this study indicate reductions in TOGW for the NLF concepts, due mainly to reductions in wing area and total wing weight. Furthermore, significant reductions in block fuel are calculated throughout the range of transition Reynolds numbers considered. Observations are made on the benefits of unsweeping the wingtips with all turbulent flow.

Fuhrmann, Henri D.

1993-01-01

171

Radiative interactions in laminar duct flows  

NASA Technical Reports Server (NTRS)

Analyses and numerical procedures are presented for infrared radiative energy transfer in gases when other modes of energy transfer occur simultaneously. Two types of geometries are considered, a parallel plate duct and a circular duct. Fully developed laminar incompressible flows of absorbing-emitting species in black surfaced ducts are considered under the conditions of uniform wall heat flux. The participating species considered are OH, CO, CO2, and H2O. Nongray as well as gray formulations are developed for both geometries. Appropriate limiting solutions of the governing equations are obtained and conduction-radiation interaction parameters are evaluated. Tien and Lowder's wide band model correlation was used in nongray formulation. Numerical procedures are presented to solve the integro-differential equations for both geometries. The range of physical variables considered are 300 to 2000 K for temperature, 0.1 to 100.0 atm for pressure, and 0.1 to 100 cm spacings between plates/radius of the tube. An extensive parametric study based on nongray formulation is presented. Results obtained for different flow conditions indicate that the radiative interactions can be quite significant in fully developed incompressible flows.

Trivedi, P. A.; Tiwari, S. N.

1990-01-01

172

A New Approach to Laminar Flowmeters  

PubMed Central

After studying the performance and characteristics of actual laminar flowmeters a new disposition for this type of sensors is proposed in such a way that the measurement errors introduced by the intrinsic nature of the device can be minimized. The preliminary study shows that the developing entry region introduces non-linearity effects in all these devices. These effects bring about not only errors, but also a change in the slope of the linear calibration respect of the Poiseuille relation. After a subsequent analysis on how these non-linearity errors can be reduced, a new disposition of this type of flowmeters is introduced. This device makes used of flow elements having pressure taps at three locations along its length and connected to three isolated chambers. In this way, the static pressure can be measured at three locations and contributed to by the pressure taps at the level of each chamber. Thus the linearization error is reduced with an additional advantage of producing a reduced pressure drop. PMID:22163486

Pena, Fernando Lopez; Diaz, Alvaro Deibe; Lema, Marcos Rodriguez; Rodriguez, Santiago Vazquez

2010-01-01

173

Laminar mixing of a compressible fluid  

NASA Technical Reports Server (NTRS)

A theoretical investigation of the velocity profiles for laminar mixing of a high-velocity stream with a region of fluid at rest has been made assuming that the Prandtl number is unity. A method which involves only quadratures is presented for calculating the velocity profile in the mixing layer for an arbitrary value of the free-stream Mach number. Detailed velocity profiles have been calculated for free-stream Mach numbers of 0, 1, 2, 3, and 5. For each Mach number, velocity profiles are presented for both a linear and a 0.76-power variation of viscosity with absolute temperature. The calculations for a linear variation are much simpler than those for a 0.76-power variation. It is shown that by selecting the constant of proportionality in the liner approximation such that it gives the correct value for the viscosity in the high-temperature part of the mixing layer, the resulting velocity profiles are in excellent agreement with those calculated by a 0.76-power variation.

Chapman, Dean R

1950-01-01

174

Transonic laminar boundary layers with surface curvature.  

NASA Technical Reports Server (NTRS)

The effect of surface curvature (both longitudinal and transverse) and the associated pressure gradient across the flow is investigated analytically for a laminar boundary layer subjected to pressure gradients along the flow. Property variation which results from heat transfer and compressibility is taken into account. Numerical solutions of the boundary layer equations are obtained for locally similar sonic flow through the throat of a nozzle for a range of flow conditions and for various shaped nozzle surfaces with different amounts of wall cooling. A few solutions were also obtained for the analogous flow around the shoulder of a flat-faced body in a supersonic flow. The effect of various parameters that arise in the equations upon application of the Levy-Mangler transformation are investigated and discussed with respect to their influence on the velocity and total enthalpy profiles and the corresponding profile slopes at the surface to which the shear stress and heat transfer are related. An important finding is that at throat Reynolds numbers less than 100,000 the heat transfer parameter at a nozzle throat decreases as the throat radius of curvature decreases.

Back, L. H.

1973-01-01

175

Modelling the Effect of Tree Foliage on Sprayer Airflow in Orchards  

NASA Astrophysics Data System (ADS)

The effect of tree foliage on sprayer airflow through pear trees in a fruit orchard was studied and modelled in detail. A new three-dimensional (3-D) computational fluid dynamics model that integrates the 3-D canopy architecture with a local closure model to simulate the effect of the stem and branches and leaves of trees separately on airflow was developed. The model was validated with field observations made in an experimental orchard (pcfruit, Sint-Truiden, Belgium) in spring and summer 2008 and was used to investigate the airflow from three air-assisted orchard sprayers (Condor V, Duoprop and AirJet quatt). Velocity magnitudes were measured before and behind leafless and fully-leafed pear canopies across the row while the operating sprayers are passing along the row, and were compared with the simulations. The simulation results predicted the measured values well with all the local relative errors within 20%. The effect of foliar density on airflow from the three air assisted sprayers was manifested by changing the magnitude and direction of the sprayers' air velocity behind the canopy, especially at the denser regions of the canopy and by changing the pattern of velocity decay horizontally along the jet. The developed methodology will also allow a thorough investigation of atmospheric airflow in canopy structures.

Melese Endalew, Ayenew; Debaer, Christof; Rutten, Nick; Vercammen, Jef; Delele, Mulugeta Admasu; Ramon, Herman; Nicolaï, Bart M.; Verboven, Pieter

2011-01-01

176

Laminar Diffusion Flame Studies (Ground- and Space-Based Studies)  

NASA Technical Reports Server (NTRS)

Laminar diffusion flames are of interest because they provide model flame systems that are far more tractable for analysis and experiments than more practical turbulent diffusion flames. Certainly, understanding flame processes within laminar diffusion flames must precede understanding these processes in more complex turbulent diffusion flames. In addition, many properties of laminar diffusion flames are directly relevant to turbulent diffusion flames using laminar flamelet concepts. Laminar jet diffusion flame shapes (luminous flame boundaries) have been of particular interest since the classical study of Burke and Schumann because they are a simple nonintrusive measurement that is convenient for evaluating flame structure predictions. Thus, consideration of laminar flame shapes is undertaken in the following, emphasizing conditions where effects of gravity are small, due to the importance of such conditions to practical applications. Another class of interesting properties of laminar diffusion flames are their laminar soot and smoke point properties (i.e., the flame length, fuel flow rate, characteristic residence time, etc., at the onset of soot appearance in the flame (the soot point) and the onset of soot emissions from the flame (the smoke point)). These are useful observable soot properties of nonpremixed flames because they provide a convenient means to rate several aspects of flame sooting properties: the relative propensity of various fuels to produce soot in flames; the relative effects of fuel structure, fuel dilution, flame temperature and ambient pressure on the soot appearance and emission properties of flames; the relative levels of continuum radiation from soot in flames; and effects of the intrusion of gravity (or buoyant motion) on emissions of soot from flames. An important motivation to define conditions for soot emissions is that observations of laminar jet diffusion flames in critical environments, e.g., space shuttle and space station facilities, cannot involve soot emitting flames in order to ensure that test chamber windows used for experimental observations are not blocked by soot deposits, thereby compromising unusually valuable experimental results. Another important motivation to define conditions where soot is present in diffusion flames is that flame chemistry, transport and radiation properties are vastly simplified when soot is absent, making such flames far more tractable for detailed numerical simulations than corresponding soot-containing flames. Motivated by these observations, the objectives of this phase of the investigation were as follows: (1) Observe flame-sheet shapes (the location of the reaction zone near phi=1) of nonluminous (soot free) laminar jet diffusion flames in both still and coflowing air and use these results to develop simplified models of flame-sheet shapes for these conditions; (2) Observe luminous flame boundaries of luminous (soot-containing) laminar jet diffusion flames in both still and coflowing air and use these results to develop simplified models of luminous flame boundaries for these conditions. In order to fix ideas here, maximum luminous flame boundaries at the laminar smoke point conditions were sought, i.e., luminous flame boundaries at the laminar smoke point; (3) Observe effects of coflow on laminar soot- and smoke-point conditions because coflow has been proposed as a means to control soot emissions and minimize the presence of soot in diffusion flames.

Dai, Z.; El-Leathy, A. M.; Lin, K.-C.; Sunderland, P. B.; Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

2000-01-01

177

The spatial and temporal distribution of tropospheric ozone laminar structures  

NASA Astrophysics Data System (ADS)

The ubiquity of ozone laminar structures in the troposphere results from complex dynamical and chemical processes in the atmosphere. We study the spatial and temporal distributions of tropospheric ozone laminar structures and the processes that control those laminar structures by using ozonesonde, ozone DIAL, and 915MHz wind profiler measurements along with HYSPLIT trajectory calculations. We present two independent methods, the Continuous Wavelet Transform (CWT) method and the gradient method, to define the ozone laminar structure in the troposphere. Temporal and spatial distributions of tropospheric ozone laminae are studied based on long-term (1999-2012) ECC ozonesonde data at four North American sites and ozone DIAL data at Huntsville AL (34.73°N, 86.65°W). We find the ozone laminae have similar vertical distribution at different seasons in Huntsville; and high frequency ozone lamina occurrence at the top of Planetary Boundary Layer (PBL), slightly low frequency around tropopause. We investigate the processes and mechanisms controlling the ozone laminae and find the ozone laminar structure is controlled by complex multiple mechanisms including the Stratosphere-to-Troposphere transport and the low-level jet transport, etc. Figure 1is an example that shows a case of an ozone lamina controlled by the nocturnal low-level jet. The results indicate ozonesondes are good for observing snapshots of atmospheric processes resulting in laminar structure, while DIAL is good for observing the temporal and spatial evolution of atmospheric processes involving laminar structures. Figure 1, Ozone DIAL measurements on 4 October 2008 at Huntsville AL retrieved with 10-min temporal integration and 750-m vertical resolution. The coincident ozonesonde measurement is marked with a triangle at the x-axis. A high ozone lamina is observed starting at 20:15 Local Time and Hysplit analysis indicate the lamina is transported from Birmingham AL approximately 160 km south of Huntsville.

Huang, G.; Newchurch, M.; kuang, S.; Wang, L.; Cantrell, W.; Johnson, B. J.; Cullis, P.

2012-12-01

178

Acoustics of laminar boundary layers breakdown  

NASA Astrophysics Data System (ADS)

Boundary layer flow transition has long been suggested as a potential noise source in both marine (sonar-dome self noise) and aeronautical (aircraft cabin noise) applications, owing to the highly transient nature of process. The design of effective noise control strategies relies upon a clear understanding of the source mechanisms associated with the unsteady flow dynamics during transition. Due to formidable mathematical difficulties, theoretical predictions either are limited to early linear and weakly nonlinear stages of transition, or employ acoustic analogy theories based on approximate source field data, often in the form of empirical correlation. In the present work, an approach which combines direct numerical simulation of the source field with the Lighthill acoustic analogy is utilized. This approach takes advantage of the recent advancement in computational capabilities to obtain detailed information about the flow-induced acoustic sources. The transitional boundary layer flow is computed by solving the incompressible Navier-Stokes equations without model assumptions, thus allowing a direct evaluation of the pseudosound as well as source functions, including the Lighthill stress tensor and the wall shear stress. The latter are used for calculating the radiated pressure field based on the Curle-Powell solution of the Lighthill equation. This procedure allows a quantitative assessment of noise source mechanisms and the associated radiation characteristics during transition from primary instability up to the laminar breakdown stage. In particular, one is interested in comparing the roles played by the fluctuating volume Reynolds stress and the wall-shear-stresses, and in identifying specific flow processes and structures that are effective noise generators.

Wang, Meng

1994-12-01

179

Acoustics of laminar boundary layers breakdown  

NASA Technical Reports Server (NTRS)

Boundary layer flow transition has long been suggested as a potential noise source in both marine (sonar-dome self noise) and aeronautical (aircraft cabin noise) applications, owing to the highly transient nature of process. The design of effective noise control strategies relies upon a clear understanding of the source mechanisms associated with the unsteady flow dynamics during transition. Due to formidable mathematical difficulties, theoretical predictions either are limited to early linear and weakly nonlinear stages of transition, or employ acoustic analogy theories based on approximate source field data, often in the form of empirical correlation. In the present work, an approach which combines direct numerical simulation of the source field with the Lighthill acoustic analogy is utilized. This approach takes advantage of the recent advancement in computational capabilities to obtain detailed information about the flow-induced acoustic sources. The transitional boundary layer flow is computed by solving the incompressible Navier-Stokes equations without model assumptions, thus allowing a direct evaluation of the pseudosound as well as source functions, including the Lighthill stress tensor and the wall shear stress. The latter are used for calculating the radiated pressure field based on the Curle-Powell solution of the Lighthill equation. This procedure allows a quantitative assessment of noise source mechanisms and the associated radiation characteristics during transition from primary instability up to the laminar breakdown stage. In particular, one is interested in comparing the roles played by the fluctuating volume Reynolds stress and the wall-shear-stresses, and in identifying specific flow processes and structures that are effective noise generators.

Wang, Meng

1994-01-01

180

Competition between pressure effects and airflow influence for the performance of plasma actuators  

SciTech Connect

The present work addresses the combined influence of pressure variations and different airflow velocities on the discharge intensity of plasma actuators. Power consumption, plasma length, and discharge capacitance were investigated systematically for varying pressure levels (p?=?0.1–1 bar) and airflow velocities (U{sub ?}=0?100 m/s) to characterize and quantify the favorable and adverse effects on the discharge intensity. In accordance with previous reports, an increasing plasma actuator discharge intensity is observed for decreasing pressure levels. At constant pressure levels, an adverse airflow influence on the electric actuator performance is demonstrated. Despite the improved discharge intensity at lower pressure levels, the seemingly improved performance of the plasma actuators is accompanied with a more pronounced drop of the relative performance. These findings demonstrate the dependency of the (kinematic and thermodynamic) environmental conditions on the electric performance of plasma actuators, which in turn affects the control authority of plasma actuators for flow control applications.

Kriegseis, J., E-mail: kriegseis@kit.edu [Institute of Fluid Mechanics, Karlsruhe Institute of Technology, Karlsruhe (Germany); Barckmann, K.; Grundmann, S., E-mail: grundmann@csi.tu-darmstadt.de [Center of Smart Interfaces, Technische Universität Darmstadt, Darmstadt (Germany); Frey, J. [Institute for Aerospace Engineering, Technische Universität Dresden, Dresden (Germany); Tropea, C. [Center of Smart Interfaces, Technische Universität Darmstadt, Darmstadt (Germany); Institute of Fluid Mechanics and Aerodynamics, Technische Universität Darmstadt, Darmstadt (Germany)

2014-05-15

181

Asbestos exposure, cigarette smoking, and airflow limitation in long-term Canadian chrysotile miners and millers  

SciTech Connect

To investigate further the relationships of asbestos exposure, cigarette smoking, and airflow limitation, we have obtained detailed pulmonary function tests (PFT) in 331 long-term Canadian chrysotile workers, 34 of whom were lifetime nonsmokers. Three disease categories were defined on the bases of standard diagnostic criteria, gallium-67 lung uptake, and the lung pressure-volume curve. Category A was composed of workers without changes suggestive of alveolitis or asbestosis. There were eight nonsmokers (ns), among whom we found a statistically significant 30% reduction in airflow conductance (Gus) at low lung volume, which is consistent with the concept of an asbestos airway lesion. The 85 smokers (sm) of category A had reduction of Gus at both high and low lung volumes. Category B was composed of workers without asbestosis but with evidence of asbestos alveolitis. In the six ns, Gus was significantly reduced to 50% normal at low lung volume. The 59 sm had reduction of Gus at both high and low lung volumes but less severely than sm in category A. Category C was composed of workers with asbestosis. The 20 ns had restrictive pattern of lung function, and Gus was decreased to 39% normal at 50% TLC. The 153 sm in C had airflow reduction comparable to sm in B. We concluded that asbestos exposure, which leads to asbestos airway disease, asbestos peribronchiolar alveolitis, and asbestosis, causes airflow limitation at low lung volume but does not reduce the expiratory flow rates on the flow-volume curve in lifetime nonsmokers. In the smoking asbestos workers with alveolitis or asbestosis, the major component of airflow limitation is a smoking effect. In these smoking workers, rigidity of the lung lessens airflow obstruction associated with smoking at the expense of increased work of breathing.

Begin, R.; Boileau, R.; Peloquin, S.

1987-01-01

182

Prevalence of airflow limitation in outpatients with cardiovascular diseases in Japan  

PubMed Central

Background and objectives Cardiovascular disease (CVD) and chronic obstructive pulmonary disease (COPD) commonly coexist and share common risk factors. The prevalence of COPD in outpatients with a smoking history and CVD in Japan is unknown. The aim of this study was to determine the proportion of Japanese patients with a smoking history being treated for CVD who have concurrent airflow limitation compatible with COPD. A secondary objective was to test whether the usage of lung function tests performed in the clinic influenced the diagnosis rate of COPD in the patients identified with airflow limitation. Methods In a multicenter observational prospective study conducted at 17 centers across Japan, the prevalence of airflow limitation compatible with COPD (defined as forced expiratory volume (FEV)1/FEV6 <0.73, by handheld spirometry) was investigated in cardiac outpatients ?40 years old with a smoking history who routinely visited the clinic for their CVD. Each patient completed the COPD Assessment Test prior to spirometry testing. Results Data were available for 995 patients with a mean age of 66.6±10.0 years, of whom 95.5% were male. The prevalence of airflow limitation compatible with COPD was 27.0% (n=269), and 87.7% of those patients (n=236) did not have a prior diagnosis of COPD. The prevalence of previously diagnosed airflow limitation was higher in sites with higher usage of lung function testing (14.0%, 15.2% respectively) compared against sites where it is performed seldom (11.1%), but was still low. Conclusion The prevalence of airflow limitation in this study indicates that a quarter of outpatients with CVD have COPD, almost all of whom are undiagnosed. This suggests that it is important to look routinely for COPD in CVD outpatients. PMID:24920894

Onishi, Katsuya; Yoshimoto, Daisuke; Hagan, Gerry W; Jones, Paul W

2014-01-01

183

How much does nasal cavity morphology matter? Patterns and rates of olfactory airflow in phyllostomid bats.  

PubMed

The morphology of the nasal cavity in mammals with a good sense of smell includes features that are thought to improve olfactory airflow, such as a dorsal conduit that delivers odours quickly to the olfactory mucosa, an enlarged olfactory recess at the back of the airway, and a clear separation of the olfactory and respiratory regions of the nose. The link between these features and having a good sense of smell has been established by functional examinations of a handful of distantly related mammalian species. In this paper, we provide the first detailed examination of olfactory airflow in a group of closely related species that nevertheless vary in their sense of smell. We study six species of phyllostomid bats that have different airway morphologies and foraging ecologies, which have been linked to differences in olfactory ability or reliance. We hypothesize that differences in morphology correlate with differences in the patterns and rates of airflow, which in turn are consistent with dietary differences. To compare species, we make qualitative and quantitative comparisons of the patterns and rates of airflow through the olfactory region during both inhalation and exhalation across the six species. Contrary to our expectations, we find no clear differences among species in either the patterns of airflow through the airway or in rates of flow through the olfactory region. By and large, olfactory airflow seems to be conserved across species, suggesting that morphological differences appear to be driven by other mechanical demands on the snout, such as breathing and feeding. Olfactory ability may depend on other aspects of the system, such as the neurobiological processing of odours that work within the existing morphology imposed by other functional demands on the nasal cavity. PMID:25520358

Eiting, Thomas P; Perot, J Blair; Dumont, Elizabeth R

2015-02-01

184

Influence of Airflow on Laboratory Storage of High Moisture Corn Stover  

SciTech Connect

Storing high moisture biomass for bioenergy use is a reality in many areas of the country where wet harvest conditions and environmental factors prevent dry storage from being feasible. Aerobic storage of high moisture biomass leads to microbial degradation and self-heating, but oxygen limitation can aid in material preservation. To understand the influence of oxygen presence on high moisture biomass (50 %, wet basis), three airflow rates were tested on corn stover stored in laboratory reactors. Temperature, carbon dioxide production, dry matter loss, chemical composition, fungal abundance, pH, and organic acids were used to monitor the effects of airflow on storage conditions. The results of this work indicate that oxygen availability impacts both the duration of self-heating and the severity of dry matter loss. High airflow systems experienced the greatest initial rates of loss but a shortened microbially active period that limited total dry matter loss (19 %). Intermediate airflow had improved preservation in short-term storage compared to high airflow systems but accumulated the greatest dry matter loss over time (up to 27 %) as a result of an extended microbially active period. Low airflow systems displayed the best performance with the lowest rates of loss and total loss (10 %) in storage at 50 days. Total structural sugar levels of the stored material were preserved, although glucan enrichment and xylan loss were documented in the high and intermediate flow conditions. By understanding the role of oxygen availability on biomass storage performance, the requirements for high moisture storage solutions may begin to be experimentally defined.

Lynn M. Wendt; Ian J. Bonner; Amber N. Hoover; Rachel M. Emerson; William A. Smith

2014-04-01

185

The Granite Mountain Atmospheric Sciences Testbed (GMAST): A Facility for Long Term Complex Terrain Airflow Studies  

NASA Astrophysics Data System (ADS)

This presentation describes a new facility at Dugway Proving Ground (DPG), Utah that can be used to study airflow over complex terrain, and to evaluate how airflow over a mountain barrier affects wind patterns over adjacent flatter terrain. DPG's primary mission is to conduct testing, training, and operational assessments of chemical and biological weapon systems. These operations require very precise weather forecasts. Most test operations at DPG are conducted on fairly flat test ranges having uniform surface cover, where airflow patterns are generally well-understood. However, the DPG test ranges are located alongside large, isolated mountains, most notably Granite Mountain, Camelback Mountain, and the Cedar Mountains. Airflows generated over, or influenced by, these mountains can affect wind patterns on the test ranges. The new facility, the Granite Mountain Atmospheric Sciences Testbed, or GMAST, is designed to facilitate studies of airflow interactions with topography. This facility will benefit DPG by improving understanding of how mountain airflows interact with the test range conditions. A core infrastructure of weather sensors around and on Granite Mountain has been developed including instrumented towers and remote sensors, along with automated data collection and archival systems. GMAST is expected to be in operation for a number of years and will provide a reference domain for mountain meteorology studies, with data useful for analysts, modelers and theoreticians. Visiting scientists are encouraged to collaborate with DPG personnel to utilize this valuable scientific resource and to add further equipment and scientific designs for both short-term and long-term atmospheric studies. Several of the upcoming MATERHORN (MountAin TERrain atmospHeric mOdeling and obseRvatioNs) project field tests will be conducted at DPG, giving an example of GMAST utilization and collaboration between DPG and visiting scientists.

Zajic, D.; Pace, J. C.; Whiteman, C. D.; Hoch, S.

2011-12-01

186

Laminar Soot Processes (LSP) Experiment: Findings From Space Flight Measurements  

NASA Technical Reports Server (NTRS)

The present experimental study of soot processes in hydrocarbon-fueled laminar nonbuoyant and nonpremixed (diffusion) flames at microgravity within a spacecraft was motivated by the relevance of soot to the performance of power and propulsion systems, to the hazards of unwanted fires, and to the emission of combustion-generated pollutants. Soot processes in turbulent flames are of greatest practical interest, however, direct study of turbulent flames is not tractable because the unsteadiness and distortion of turbulent flames limit available residence times and spatial resolution within regions where soot processes are important. Thus, laminar diffusion flames are generally used to provide more tractable model flame systems to study processes relevant to turbulent diffusion flames, justified by the known similarities of gas-phase processes in laminar and turbulent diffusion flames, based on the widely-accepted laminar flamelet concept of turbulent flames. Unfortunately, laminar diffusion flames at normal gravity are affected by buoyancy due to their relatively small flow velocities and, as discussed next, they do not have the same utility for simulating the soot processes as they do for simulating the gas phase processes of turbulent flames.

Sunderland, P. B.; Urban, D. L.; Yuan, Z. G.; Aalburg, C.; Diez, F. J.; Faeth, G. M.

2003-01-01

187

Computational Analysis of the G-III Laminar Flow Glove  

NASA Technical Reports Server (NTRS)

Under NASA's Environmentally Responsible Aviation Project, flight experiments are planned with the primary objective of demonstrating the Discrete Roughness Elements (DRE) technology for passive laminar flow control at chord Reynolds numbers relevant to transport aircraft. In this paper, we present a preliminary computational assessment of the Gulfstream-III (G-III) aircraft wing-glove designed to attain natural laminar flow for the leading-edge sweep angle of 34.6deg. Analysis for a flight Mach number of 0.75 shows that it should be possible to achieve natural laminar flow for twice the transition Reynolds number ever achieved at this sweep angle. However, the wing-glove needs to be redesigned to effectively demonstrate passive laminar flow control using DREs. As a by-product of the computational assessment, effect of surface curvature on stationary crossflow disturbances is found to be strongly stabilizing for the current design, and it is suggested that convex surface curvature could be used as a control parameter for natural laminar flow design, provided transition occurs via stationary crossflow disturbances.

Malik, Mujeeb R.; Liao, Wei; Lee-Rausch, Elizabeth M.; Li, Fei; Choudhari, Meelan M.; Chang, Chau-Lyan

2011-01-01

188

Assessment of LAURA for Laminar Supersonic Shallow Cavities  

NASA Technical Reports Server (NTRS)

The ability of the Laura flow solver to predict local heating augmentation factors for shallow cavities is assessed. This assessment is part of a larger e ort within the Space Shuttle return-to-flight program to develop technologies to support on-orbit tile repair decisions. The comparison is made against global phosphor thermography images taken in the Langley Aerothermodynamic Laboratory 20-Inch Mach 6 Air Tunnel. The cavities are rectangular in shape, with lengths L/H of 14 20 and depths H/ of 1.1 5.2. The fully laminar results, for Re = 300, show good agreement between the data sets. For Re = 503, the wind tunnel data indicates boundary layer transition with turbulent flow both within and downstream of the cavity. The turbulent flow structures are significantly di erent from the laminar predictions, with order of magnitude increases in the heating augmentations. Because of the di erent flow structures, no simple bump factor can be used to correct the laminar calculations to account for the turbulent heating levels. A fine gradation in wind tunnel cases will be required to clearly delineate the laminar-to-turbulent transition point, and hence the limits of applicability of the laminar numerical approach.

Wood, William A.; Pulsonetti, Maria V.; Everhart, Joel L.; Bey, Kim S.

2004-01-01

189

Brief history of laminar flow clean room systems  

SciTech Connect

This paper reviews the development and evolution of laminar flow clean rooms and hoods and describes the underlying principles and rationales associated with development of this type of clean room system and Federal Standard No. 209. By the mid 1970's, over a thousand hospitals in the US had installed laminar flow equipment in operating rooms. During the past several years a great deal of attention has been focused on conserving energy in clean rooms. Some gains in energy conservation have been achieved by improved design, off hours shutdown, and closer evaluation of requirements for clean rooms. By the early 1970's, the laminar flow principle had been carried from the Laboratory and applied to production hardware to create a mature industry producing and marketing a variety of laminar flow equipment in less than 10 years time. This achievement was made possible by literally dozens of persons in industry, government, military, and private individuals who developed hardware, added numerous innovations, and had the foresight to apply the technology to many fields other than industrial clean rooms. Now, with laminar flow devices available, class 100 levels are readily achievable and maintained, and at the same time require fewer operating restrictions than previously possible.

Whitfield, W J

1981-01-01

190

Reexamination of the Near-Surface Airflow over the Antarctic Continent and Implications on Atmospheric Circulations at High Southern Latitudes*  

E-print Network

Reexamination of the Near-Surface Airflow over the Antarctic Continent and Implications) ABSTRACT Previous work has shown that winds in the lower atmosphere over the Antarctic continent are among the mean annual and seasonal airflow patterns over the Antarctic continent to compare with previous

Howat, Ian M.

191

Procedure and Application for Determining the Cold Deck and Hot Deck Airflow in a Dual-Duct System  

E-print Network

as Equation 2, which is derived by the fan laws: 22120 '' QaQaaH ?+?+= ?? (2) where: ? is a current fan speed over 100% fan speed. Q? is a calculated airflow rate under partial speed of the fan. The airflow rate...

Liu, G.; Mingsheng, L.

2006-01-01

192

Differences in Airway Inflammation in Patients with Fixed Airflow Obstruction Due to Asthma or Chronic Obstructive Pulmonary Disease  

Microsoft Academic Search

To determine whether patients with fixed airflow obstruction have tory symptoms after airflow obstruction is already fixed. distinct pathologic and functional characteristics depending on a These patients are often diagnosed as having COPD, even history of either asthma or chronic obstructive pulmonary disease if the differential diagnosis between asthma and COPD in (COPD), we characterized 46 consecutive outpatients presenting patients

Leonardo M. Fabbri; Micaela Romagnoli; Lorenzo Corbetta; Gianluca Casoni; Kamelija Busljetic; Graziella Turato; Guido Ligabue; Adalberto Ciaccia; Marina Saetta; Alberto Papi

193

Measurement of Airflow around the Human Body with Wide-cover Type Personal Air-conditioning with PIV  

Microsoft Academic Search

Many existing personal air-conditioning systems cool only specific portions of the human body in the form of spot cooling, using either cooled or fast airflow to control thermal sensation. This may cause various problems related to localized airflow, such as discomfort to the face and neck areas and dryness in the eyes. Therefore, a method is proposed in this research

Jeong-Hoon Yang; Shinsuke Kato; Ho-Tae Seok

2009-01-01

194

Method for laminar boundary layer transition visualization in flight  

NASA Technical Reports Server (NTRS)

Disclosed is a method of visualizing laminar to turbulent boundary layer transition, shock location, and laminar separation bubbles around a test surface. A liquid crystal coating is formulated using an unencapsulated liquid crystal operable in a temperature bandwidth compatible with the temperature environment around the test surface. The liquid crystal coating is applied to the test surface, which is preferably pretreated by painting with a flat, black paint to achieve a deep matte coating, after which the surface is subjected to a liquid or gas flow. Color change in the liquid crystal coating is produced in response to differences in relative shear stress within the boundary layer around the test surface. The novelty of this invention resides in the use of liquid crystals which are sensitive to shear stress to show aerodynamic phenomena such as a boundary layer transition, shock location, and laminar separation bubbles around a test surface.

Holmes, Bruce J. (inventor); Gall, Peter D. (inventor)

1988-01-01

195

Design of a hybrid laminar flow control nacelle  

NASA Technical Reports Server (NTRS)

Consideration is given to the potential application of hybrid-laminar-flow control to the external surface of a modern, high-bypass-ratio (HBR) turbofan engine nacelle. With the advent of advanced ultra-HBR fans (with bypass ratios of 10-15), the wetted areas of these nacelles approach 10 percent of the total wetted area of future commercial transports. A hybrid-laminar-flow-control pressure distribution is specified and the corresponding nacelle geometry is computed utilizing a predictor/corrector design method. Linear stability calculations are conducted to provide predictions of the extent of the laminar boundary layer. Performance studies on an advanced twin-engine transport configuration are presented to determine potential benefits in terms of reduced fuel consumption.

Wie, Yong-Sun; Collier, Fayette S., Jr.; Wagner, Richard D.; Viken, Jeffery K.; Pfenninger, Werner

1992-01-01

196

Laminar boundary layer instability noise produced by an aerofoil  

NASA Astrophysics Data System (ADS)

When a laminar boundary layer exists on the surface of an aerofoil up to the trailing edge, a tone or a number of tones are sometimes produced. These tones have been the subject of a number of investigations which have proposed a variety of different mechanisms regarding their production. This paper gives a brief overview of the previously proposed mechanisms and then describes the development of a theoretical model to estimate the tone frequencies. The model is validated against a number of well-known published experiments and also against the results of an experimental investigation undertaken by the authors. The model is compared with other models available for predicting laminar boundary layer instability noise and is shown to be accurate and robust. Unlike previous models, which are empirical, the model presented in this paper is purely theoretical and could be used to predict the frequency of laminar boundary layer instability noise produced by an arbitrary aerofoil.

Kingan, Michael J.; Pearse, John R.

2009-05-01

197

Lockheed laminar-flow control systems development and applications  

NASA Technical Reports Server (NTRS)

Progress is summarized from 1974 to the present in the practical application of laminar-flow control (LFC) to subsonic transport aircraft. Those efforts included preliminary design system studies of commercial and military transports and experimental investigations leading to the development of the leading-edge flight test article installed on the NASA JetStar flight test aircraft. The benefits of LFC on drag, fuel efficiency, lift-to-drag ratio, and operating costs are compared with those for turbulent flow aircraft. The current activities in the NASA Industry Laminar-Flow Enabling Technologies Development contract include summaries of activities in the Task 1 development of a slotted-surface structural concept using advanced aluminum materials and the Task 2 preliminary conceptual design study of global-range military hybrid laminar flow control (HLFC) to obtain data at high Reynolds numbers and at Mach numbers representative of long-range subsonic transport aircraft operation.

Lange, Roy H.

1987-01-01

198

Laminar and intermittent flow in a tilted heat pipe.  

PubMed

Heat transfer measurements performed by Riedinger et al. (Phys. Fluids, 25, 015117 (2013)) showed that in an inclined channel, heated from below and cooled from above with adiabatic walls, the flow is laminar or intermittent (local bursts can occur in the laminar flow) when the inclination angle is sufficiently high and the applied power sufficiently low. In this case, gravity plays a crucial role in the characteristics of the flow. In this paper, we present velocity measurements, and their derived tensors, obtained with Particle Image Velocimetry inside the channel. We, also, propose a model derived from a jet interpretation of the flow. Comparison between experiment and model shows a fair agreement. PMID:24464137

Rusaouen, E; Riedinger, X; Tisserand, J-C; Seychelles, F; Salort, J; Castaing, B; Chillà, F

2014-01-01

199

DNS of Reacting H2/Air Laminar Vortex Rings and Krishnan Mahesh  

E-print Network

DNS of Reacting H2/Air Laminar Vortex Rings Jeff Doom and Krishnan Mahesh University of Minnesota, Minneapolis, MN, 55455, USA Direct numerical simulation (DNS) is used to study reacting, laminar vortex rings

Mahesh, Krishnan

200

Computational Evaluation of a Transonic Laminar-Flow Wing Glove Design  

E-print Network

The aerodynamic benefits of laminar flow have long made it a sought-after attribute in aircraft design. By laminarizing portions of an aircraft, such as the wing or empennage, significant reductions in drag could be achieved, reducing fuel burn...

Roberts, Matthew William

2012-07-16

201

Citric acid cough threshold and airway responsiveness in asthmatic patients and smokers with chronic airflow obstruction.  

PubMed Central

The relation between citric acid cough threshold and airway hyperresponsiveness was investigated in 11 non-smoking patients with allergic asthma (mean FEV1 94% predicted) and 25 non-atopic smokers with chronic airflow obstruction (mean FEV1 65% predicted). Cough threshold was determined on two occasions by administering doubling concentrations of citric acid. Seven of the 11 asthmatic subjects and 14 of 25 smokers with chronic airflow obstruction had a positive cough threshold on both test days. Cough threshold measurements were reproducible in both groups (standard deviation of duplicate measurements 1.2 doubling concentrations in asthma, 1.1 doubling concentrations in chronic airflow obstruction). Citric acid provocation did not cause bronchial obstruction in most patients, though four patients had a fall in FEV1 of more than 20% for a short time on one occasion only. No significant difference in cough threshold was found between the two patient groups despite differences in baseline FEV1 values. There was no significant correlation between cough threshold and the provocative concentration of histamine causing a 20% fall in FEV1 (PC20) histamine in either group. Thus sensory nerves can be activated with a tussive agent in patients with asthma and chronic airflow obstruction without causing bronchial smooth muscle contraction. PMID:1948792

Auffarth, B; de Monchy, J G; van der Mark, T W; Postma, D S; Koëter, G H

1991-01-01

202

Performance of Supply Airflow Entrainment for Particles in an Underfloor Air Distribution System  

E-print Network

comfort conditions and energy conservation. However, the supply air outlet of UFAD system is set on the floor, such that the supply airflow may entrain the dust particles settled on the floor or suspended near the floor. This creates problems that need...

Li, C.; Li, N.

2006-01-01

203

Computational Fluid Dynamics Simulation of Airflow and Aerosol Deposition in Human Lungs  

Microsoft Academic Search

Computational fluid dynamics (CFD) simulations of airflow and particle deposition in geometries representing the human tracheobronchial tree were conducted. Two geometries were used in this work: (1) based on the Weibel A model, and (2) based on a CT scan of a cadaver lung cast. Flow conditions used included both steady-state inhalation and exhalation conditions as well as time-dependent breathing

Natalya Nowak; Prashant P. Kakade; Ananth V. Annapragada

2003-01-01

204

Test-Retest Reliability of Respiratory Resistance Measured with the Airflow Perturbation Device  

ERIC Educational Resources Information Center

Purpose: In this study, the authors aimed to determine reliability of the airflow perturbation device (APD) to measure respiratory resistance within and across sessions during resting tidal (RTB) and postexercise breathing in healthy athletes, and during RTB across trials within a session in athletes with paradoxical vocal fold motion (PVFM)…

Gallena, Sally K.; Solomon, Nancy Pearl; Johnson, Arthur T.; Vossoughi, Jafar; Tian, Wei

2014-01-01

205

Using the Torque Characteristics of Dampers to Measure Airflow, Part II: Analysis and Testing  

Microsoft Academic Search

This paper describes the analysis and testing of a method of measuring airflow from position and torque (APT) measurements of dampers. The method is based on a newly developed mathematical model of the aerodynamic torque characteristics of dampers. An uncertainty analysis demonstrates that the APT method can outperform a pitot tube over a wide range of conditions, but that it

Clifford Federspiel

2004-01-01

206

Airflow produced by dielectric barrier discharge between asymmetric parallel rod electrodes  

SciTech Connect

We observed a novel type of airflow produced by an atmospheric rf discharge between asymmetric parallel rod electrodes. The electrodes were a bare metal rod 1 mm in diameter and a glass-coated metal rod 3.2 mm in diameter. The thrust, measured by a pendulum, increased with discharge input power.

Hayashi, Kazuo; Tanaka, Motofumi; Yasui, Hiroyuki; Hashimoto, Kiyoshi [Power and Industrial Systems Research and Development Center, Toshiba Corporation, Power Systems Company, 20-1 Kansei-cho, Tsurumi-ku, Yokohama 230-0034 (Japan); Toshiba Business and Life Service Corporation, 7-1 Nisshin-cho, Kawasaki-ku, Kawasaki 210-0024 (Japan)

2007-09-15

207

Evaluation of Airflow Patterns in the Transfer Area of the 105 KE Basin  

SciTech Connect

This report is a qualitative study of airflow patterns within a building at the transfer area of the 105 KE Basin on the Hanford Site in Washington State. The purpose of the study was to determine the appropriate location for air monitoring equipment.

Fritz, Brad G.; Khan, Fenton; Mendoza, Donaldo P.

2003-03-07

208

Numerical Simulation and Experimental Study on Airflow Characteristics in the Plenum of Underfloor Air Supply  

E-print Network

factors, air velocity and beam height, affect the airflow in the plenum. Pressure loss mainly occurs around the beam. In the underfloor plenum the structural design should reduce the crossbeam height as much as possible, and in operation should reduce air...

Li, X.; Li, N.; Fang, F.; Zhao, D.

2006-01-01

209

Risk factors for persistent airflow limitation: Analysis of 306 patients with asthma  

PubMed Central

Objectives : To determine the risk factors associated with persistent airflow limitation in patients with asthma. Method s: This study was designed and carried out in the department of respiratory medicine, fourth People’s Hospital of Jinan City, Shandong province, China between Jan 2012 and Dec 2012. Three hundred and six asthma patients participating in the study were divided into persistent airflow limitation group (PAFL) and no persistent airflow limitation group (NPAFL). The patients participated in pulmonary function tests and sputum induction examination. The clinical data including age, gender, onset age, disease course, smoking history, family history, regular corticosteroid inhalation, hospitalization history and presence of atopy were collected. Results : In 306 patients, 128 (40.5%) were included in PAFL group and 178(59.5%) in NPAFL group. Multivariate analysis demonstrated smoking (?10 pack-years; OR, 7.1; 95% CI, 1.8 to 31.2), longer asthma duration (? 20years) (OR, 6.3; 95% CI, 1.7 to 28.5), absence of regular corticosteroid inhalation (OR, 3.5; 95% CI, 1.1 to 14.5) and neutrophil in induced sputum?65% (OR, 1.8; 95% CI, 1.0 to 2.8) were independent risk factors for PAFL. Conclusions : Smoking, longer asthma duration and increased neutrophil in induced sputum are risk factors for PAFL, while regular corticosteroid inhalation is protective factor. Smoking cessation and regular corticosteroid inhalation may play an important role in preventing the occurrence of persistent airflow limitation group (PAFL).

Wang, Lingcheng; Gao, Shuncui; Zhu, Wei; Su, Jun

2014-01-01

210

EMI from airflow aperture arrays in shielding enclosures-experiments, FDTD, and MoM modeling  

Microsoft Academic Search

Aperture arrays designed to provide airflow through shielding enclosures can provide part of the coupling path from interior sources to external electromagnetic interference (EMI). In this work, radiation through aperture arrays is investigated numerically and experimentally. FDTD modeling is compared with measurements on aperture arrays in a test enclosure. The method of moments (MoM) is also utilized to study radiation

Min Li; Joe Nuebel; James L. Drewniak; Richard E. DuBroff; Todd H. Hubing; Thomas P. Van Doren

2000-01-01

211

Using a closed nose chamber for airflow measurements in a transfer impedance system  

Microsoft Academic Search

A transfer impedance system has been developed for noninvasive monitoring of the respiratory mechanics in a mouse. The animal's thorax is exposed to pressure oscillations, which induce a flow through the airway opening. By oscillating with a large range of frequencies, one can determine the frequency response from applied thoracic pressure to generated airflow through the nose. The pressure variations

S. P. Juhlin; T. M. Wendel

1999-01-01

212

One-dimensional airflow in unsaturated zone induced by periodic water table fluctuation  

Microsoft Academic Search

This paper investigates the vertical airflow driven by fluctuating water table within the lower layer of a coastal two-layered system. The upper layer is unsaturated and semipermeable, while the lower is permeable. An analytical solution of the subsurface air pressure fluctuation is derived on the basis of model simplification assumptions, the reasonability of which was examined by numerical solutions of

Hailong Li; Jiu Jimmy Jiao

2005-01-01

213

Experimental investigation of transient thermal behavior of an airship under different solar radiation and airflow conditions  

NASA Astrophysics Data System (ADS)

Knowledge of the thermal behavior of airships is crucial to the development of airship technology. An experiment apparatus is constructed to investigate the thermal response characteristics of airships, and the transient temperature distributions of both hull and inner gas are obtained under the irradiation of a solar simulator and various airflow conditions. In the course of the research, the transient temperature change of the experimental airship is measured for four airflow speeds of 0 m/s (natural convection), 3.26 m/s, 5.5 m/s and 7.0 m/s, and two incident solar radiation values of 842.4 W/m2 and 972.0 W/m2. The results show that solar irradiation has significant influence on the airship hull and inner gas temperatures even if the airship stays in a ground airflow environment where the heat transfer is dominated by radiation and convection. The airflow around the airship is conducive to reduce the hull temperature and temperature nonuniformity. Transient thermal response of airships rapidly varies with time under solar radiation conditions and the hull temperature remains approximately constant in ˜5-10 min. Finally, a transient thermal model of airship is developed and the model is validated through comparison with the experimental data.

Li, De-Fu; Xia, Xin-Lin; Sun, Chuang

2014-03-01

214

Characterization of turbulent airflow over evolving water-waves in a wind-wave tank  

NASA Astrophysics Data System (ADS)

Results of an experimental investigation of the turbulent boundary layer in airflow over evolving young wind-waves are presented. The experiments were conducted in a laboratory wind-wave flume consisting of a closed-loop wind tunnel capable of generating wind speed that may exceed 15 m/s, atop of a 5 m long wave tank. Simultaneous measurements of mean wind velocity and of instantaneous fluctuations of the horizontal and vertical air velocity components were carried out along the test section at different airflow rates and at numerous heights above the highest wave. Instantaneous surface elevation at the air sensors' location was simultaneously recorded. The friction velocities at all locations and for all airflow rates were determined by two independent methods: by fitting the logarithmic velocity profiles and by extrapolating the measured Reynolds shear stresses to mean water surface level. The variation with height and along the test section of the fluctuations of two velocity components, in the mean flow and in the vertical directions, was also studied and the results compared with flow behavior over rough and smooth plates. Wave-induced airflow parameters were then investigated by application of cross-spectral analysis. Results on the vertical extent of wave-induced boundary layer, on the phase relation between the wave-induced velocity fluctuations and the surface elevation, as well as on the wave-induced Reynolds shear stress are reported.

Zavadsky, Andrey; Shemer, Lev

2012-11-01

215

Detection of Mouse Cough Based on Sound Monitoring and Respiratory Airflow Waveforms  

PubMed Central

Detection for cough in mice has never yielded clearly audible sounds, so there is still a great deal of debates as to whether mice can cough in response to tussive stimuli. Here we introduce an approach for detection of mouse cough based on sound monitoring and airflow signals. 40 Female BALB/c mice were pretreated with normal saline, codeine, capasazepine or desensitized with capsaicin. Single mouse was put in a plethysmograph, exposed to aerosolized 100 µmol/L capsaicin for 3 min, followed by continuous observation for 3 min. Airflow signals of total 6 min were recorded and analyzed to detect coughs. Simultaneously, mouse cough sounds were sensed by a mini-microphone, monitored manually by an operator. When manual and automatic detection coincided, the cough was positively identified. Sound and sound waveforms were also recorded and filtered for further analysis. Body movements were observed by operator. Manual versus automated counts were compared. Seven types of airflow signals were identified by integrating manual and automated monitoring. Observation of mouse movements and analysis of sound waveforms alone did not produce meaningful data. Mouse cough numbers decreased significantly after all above drugs treatment. The Bland-Altman and consistency analysis between automatic and manual counts was 0.968 and 0.956. The study suggests that the mouse is able to present with cough, which could be detected by sound monitoring and respiratory airflow waveform changes. PMID:23555643

Chen, Liyan; Lai, Kefang; Lomask, Joseph Mark; Jiang, Bert; Zhong, Nanshan

2013-01-01

216

Validation of GCM control simulations using indices of daily airflow types over the British Isles  

Microsoft Academic Search

In this study, the control simulations of two general circulation model (GCM) experiments are assessed in terms of their ability to reproduce realistic ‘real world’ weather. The models examined are the UK Meteorological Office high-resolution atmospheric model (UKHI) and a coupled ocean\\/atmosphere model of the Max Planck Institut für Meteorologic, Hamburg (MPI). An objective classification of daily airflow patterns over

M Hulme; K R Briffal; P D Jones; C A Senior

1993-01-01

217

Considerations for Efficient Airflow Design in Cleanrooms Tengfang Xu, Ph.D., PE,  

E-print Network

designs: #12;fan-tower (FT) with pressurized-plenum distributed air handler unit (AHU) fan-filter unitConsiderations for Efficient Airflow Design in Cleanrooms Tengfang Xu, Ph.D., PE, Lawrence Berkeley in addition to effective contamination control. Energy-efficient designs can yield capital and operational

218

ENVIRONMENTAL TECHNOLOGY VERIFICATION, TEST REPORT OF CONTROL OF BIOAEROSOLS IN HVAC SYSTEMS, AIRFLOW PRODUCTS AFP30  

EPA Science Inventory

The Environmental Technology Verification report discusses the technology and performance of the AFP30 air filter for dust and bioaerosol filtration manufactured by Airflow Products. The pressure drop across the filter was 62 Pa clean and 247 Pa dust loaded. The filtration effici...

219

Effect of reduced evaporator airflow on the high temperature performance of air conditioners  

Microsoft Academic Search

Two residential sized air conditioners were tested in psychrometric rooms at reduced evaporator airflows ranging from 0 to 50% below that recommended by the manufacture of each of the units. Outdoor temperatures ranged from 35 to 49°C. One of the units used a thermal expansion valve for flow control while the other unit used a short tube orifice. Performance of

Angel G. Rodriguez; Dennis O'Neal; Michael Davis; Sekhar Kondepudi

1996-01-01

220

Further experiments on the stability of laminar and turbulent hydrogen-air flames at reduced pressures  

NASA Technical Reports Server (NTRS)

Stability limits for laminar and turbulent hydrogen-air burner flames were measured as a function of pressure, burner diameter, and composition. On the basis of a simple flame model, turbulent flashback involved a smaller effective penetration distance than laminar flashback. No current theoretical treatment predicts the observed pressure and diameter dependence of laminar and turbulent blowoff.

Fine, Burton

1957-01-01

221

Thermal Infrared Imaging: A Novel Method to Monitor Airflow During Polysomnography  

PubMed Central

Study Objectives: This is a feasibility study designed to evaluate the accuracy of thermal infrared imaging (TIRI) as a noncontact method to monitor airflow during polysomnography and to ascertain the chance-corrected agreement (?) between TIRI and conventional airflow channels (nasal pressure [Pn], oronasal thermistor and expired CO2 [PECO2]) in the detection of apnea and hypopnea. Design: Subjects were recruited to undergo polysomnography for 1 to 2 hours, during which simultaneous recordings from electroencephalography, electrooculography, electromyography, respiratory impedance plethysmography, conventional airflow channels, and TIRI were obtained. Setting: University-affiliated, American Academy of Sleep Medicine-accredited sleep disorders center. Patients or Participants: Fourteen volunteers without a history of sleep disordered breathing and 13 patients with a history of obstructive sleep apnea were recruited. Measurements and Results: In the detection of apnea and hypopnea, excellent agreement was noted between TIRI and thermistor (? = 0.92, Bayesian Credible Interval [BCI] 0.86, 0.96; p? = 0.99). Good agreement was noted between TIRI and Pn (? = 0.83, BCI 0.70, 0.90; p? = 0.98) and between TIRI and PECO2(? = 0.80, BCI 0.66, 0.89; p? = 0.94). Conclusions: TIRI is a feasible noncontact technology to monitor airflow during polysomnography. In its current methodologic incarnation, it demonstrates a high degree of chance-corrected agreement with the oronasal thermistor in the detection of apnea and hypopneas but demonstrates a lesser degree of chance-corrected agreement with Pn. Further overnight validation studies must be performed to evaluate its potential in clinical sleep medicine. Citation: Murthy JN; van Jaarsveld J; Fei J; Pavlidis I; Harrykissoon R; Lucke JF; Faiz S; Castriotta RJ. Thermal infrared imaging: a novel method to monitor airflow during polysomnography. SLEEP 2009;32(11):1521-1527. PMID:19928392

Murthy, Jayasimha N.; van Jaarsveld, Johan; Fei, Jin; Pavlidis, Ioannis; Harrykissoon, Rajesh I; Lucke, Joseph F.; Faiz, Saadia; Castriotta, Richard J.

2009-01-01

222

Pulmonary anatomy in the Nile crocodile and the evolution of unidirectional airflow in Archosauria  

PubMed Central

The lungs of birds have long been known to move air in only one direction during both inspiration and expiration through most of the tubular gas-exchanging bronchi (parabronchi). Recently a similar pattern of airflow has been observed in American alligators, a sister taxon to birds. The pattern of flow appears to be due to the arrangement of the primary and secondary bronchi, which, via their branching angles, generate inspiratory and expiratory aerodynamic valves. Both the anatomical similarity of the avian and alligator lung and the similarity in the patterns of airflow raise the possibility that these features are plesiomorphic for Archosauria and therefore did not evolve in response to selection for flapping flight or an endothermic metabolism, as has been generally assumed. To further test the hypothesis that unidirectional airflow is ancestral for Archosauria, we measured airflow in the lungs of the Nile crocodile (Crocodylus niloticus). As in birds and alligators, air flows cranially to caudally in the cervical ventral bronchus, and caudally to cranially in the dorsobronchi in the lungs of Nile crocodiles. We also visualized the gross anatomy of the primary, secondary and tertiary pulmonary bronchi of C. niloticus using computed tomography (CT) and microCT. The cervical ventral bronchus, cranial dorsobronchi and cranial medial bronchi display similar characteristics to their proposed homologues in the alligator, while there is considerable variation in the tertiary and caudal group bronchi. Our data indicate that the aspects of the crocodilian bronchial tree that maintain the aerodynamic valves and thus generate unidirectional airflow, are ancestral for Archosauria. PMID:23638399

Hutchinson, John R.; Farmer, CG

2013-01-01

223

Pulmonary anatomy in the Nile crocodile and the evolution of unidirectional airflow in Archosauria.  

PubMed

The lungs of birds have long been known to move air in only one direction during both inspiration and expiration through most of the tubular gas-exchanging bronchi (parabronchi). Recently a similar pattern of airflow has been observed in American alligators, a sister taxon to birds. The pattern of flow appears to be due to the arrangement of the primary and secondary bronchi, which, via their branching angles, generate inspiratory and expiratory aerodynamic valves. Both the anatomical similarity of the avian and alligator lung and the similarity in the patterns of airflow raise the possibility that these features are plesiomorphic for Archosauria and therefore did not evolve in response to selection for flapping flight or an endothermic metabolism, as has been generally assumed. To further test the hypothesis that unidirectional airflow is ancestral for Archosauria, we measured airflow in the lungs of the Nile crocodile (Crocodylus niloticus). As in birds and alligators, air flows cranially to caudally in the cervical ventral bronchus, and caudally to cranially in the dorsobronchi in the lungs of Nile crocodiles. We also visualized the gross anatomy of the primary, secondary and tertiary pulmonary bronchi of C. niloticus using computed tomography (CT) and microCT. The cervical ventral bronchus, cranial dorsobronchi and cranial medial bronchi display similar characteristics to their proposed homologues in the alligator, while there is considerable variation in the tertiary and caudal group bronchi. Our data indicate that the aspects of the crocodilian bronchial tree that maintain the aerodynamic valves and thus generate unidirectional airflow, are ancestral for Archosauria. PMID:23638399

Schachner, Emma R; Hutchinson, John R; Farmer, Cg

2013-01-01

224

Usability Evaluation of a Flight-Deck Airflow Hazard Visualization System  

NASA Technical Reports Server (NTRS)

Many aircraft accidents each year are caused by encounters with unseen airflow hazards near the ground, such as vortices, downdrafts, low level wind shear, microbursts, or turbulence from surrounding vegetation or structures near the landing site. These hazards can be dangerous even to airliners; there have been hundreds of fatalities in the United States in the last two decades attributable to airliner encounters with microbursts and low level wind shear alone. However, helicopters are especially vulnerable to airflow hazards because they often have to operate in confined spaces and under operationally stressful conditions (such as emergency search and rescue, military or shipboard operations). Providing helicopter pilots with an augmented-reality display visualizing local airflow hazards may be of significant benefit. However, the form such a visualization might take, and whether it does indeed provide a benefit, had not been studied before our experiment. We recruited experienced military and civilian helicopter pilots for a preliminary usability study to evaluate a prototype augmented-reality visualization system. The study had two goals: first, to assess the efficacy of presenting airflow data in flight; and second, to obtain expert feedback on sample presentations of hazard indicators to refine our design choices. The study addressed the optimal way to provide critical safety information to the pilot, what level of detail to provide, whether to display specific aerodynamic causes or potential effects only, and how to safely and effectively shift the locus of attention during a high-workload task. Three-dimensional visual cues, with varying shape, color, transparency, texture, depth cueing, and use of motion, depicting regions of hazardous airflow, were developed and presented to the pilots. The study results indicated that such a visualization system could be of significant value in improving safety during critical takeoff and landing operations, and also gave clear indications of the best design choices in producing the hazard visual cues.

Aragon, Cecilia R.

2004-01-01

225

Estimation of Laminar Burning Velocities by Direct Digital Photography  

ERIC Educational Resources Information Center

The Bunsen burner flame, which is the most common flame in the laboratory, can be easily studied for its dynamics because of modern, economical digital technology available to student laboratories. Direct digital photography of Bunsen flames is used to obtain laminar burning velocities of selected gaseous hydrocarbon/air flames.

Uske, J.; Barat, R.

2004-01-01

226

Electrostatic quadrupole focused particle accelerating assembly with laminar flow beam  

DOEpatents

A charged particle accelerating assembly provided with a predetermined ratio of parametric structural characteristics and with related operating voltages applied to each of its linearly spaced focusing and accelerating quadrupoles, thereby to maintain a particle beam traversing the electrostatic fields of the quadrupoles in the assembly in an essentially laminar flow through the assembly.

Maschke, A.W.

1984-04-16

227

Computational Optimization of a Natural Laminar Flow Experimental Wing Glove  

NASA Technical Reports Server (NTRS)

Computational optimization of a natural laminar flow experimental wing glove that is mounted on a business jet is presented and discussed. The process of designing a laminar flow wing glove starts with creating a two-dimensional optimized airfoil and then lofting it into a three-dimensional wing glove section. The airfoil design process does not consider the three dimensional flow effects such as cross flow due wing sweep as well as engine and body interference. Therefore, once an initial glove geometry is created from the airfoil, the three dimensional wing glove has to be optimized to ensure that the desired extent of laminar flow is maintained over the entire glove. TRANAIR, a non-linear full potential solver with a coupled boundary layer code was used as the main tool in the design and optimization process of the three-dimensional glove shape. The optimization process uses the Class-Shape-Transformation method to perturb the geometry with geometric constraints that allow for a 2-in clearance from the main wing. The three-dimensional glove shape was optimized with the objective of having a spanwise uniform pressure distribution that matches the optimized two-dimensional pressure distribution as closely as possible. Results show that with the appropriate inputs, the optimizer is able to match the two dimensional pressure distributions practically across the entire span of the wing glove. This allows for the experiment to have a much higher probability of having a large extent of natural laminar flow in flight.

Hartshom, Fletcher

2012-01-01

228

Combustion Module-1 with Laminar Soot Process (LSP)  

NASA Technical Reports Server (NTRS)

Technicians install the Laminar Soot Processes (LSP) experiment into the combustion chamber of Combustion Module-1. CM-1 was one of the most complex and technologically sophisticated pieces of hardware ever to be included as a part of a Spacelab mission.

2004-01-01

229

Laminar drag reduction in microchannels using ultrahydrophobic surfaces  

Microsoft Academic Search

A series of experiments is presented which demonstrate significant drag reduction for the laminar flow of water through microchannels using hydrophobic surfaces with well-defined micron-sized surface roughness. These ultrahydrophobic surfaces are fabricated from silicon wafers using photolithography and are designed to incorporate precise patterns of microposts and microridges which are made hydrophobic through a chemical reaction with an organosilane. An

Jia Ou; Blair Perot; Jonathan P. Rothstein

2004-01-01

230

Application of laminar flow control to supersonic transport configurations  

NASA Technical Reports Server (NTRS)

The feasibility and impact of implementing a laminar flow control system on a supersonic transport configuration were investigated. A hybrid laminar flow control scheme consisting of suction controlled and natural laminar flow was developed for a double-delta type wing planform. The required suction flow rates were determined from boundary layer stability analyses using representative wing pressure distributions. A preliminary design of structural modifications needed to accommodate suction through a perforated titanium skin was carried out together with the ducting and systems needed to collect, compress and discharge the suction air. The benefits of reduced aerodynamic drag were weighed against the weight, volume and power requirement penalties of suction system installation in a mission performance and sizing program to assess the net benefits. The study showed a feasibility of achieving significant laminarization of the wing surface by use of a hybrid scheme, leading to an 8.2 percent reduction in the cruise drag. This resulted in an 8.5 percent reduction in the maximum takeoff weight and a 12 percent reduction in the fuel burn after the inclusion of the LFC system installation penalties. Several research needs were identified for a resolution of aerodynamics, structural and systems issues before these potential benefits could be realized in a practical system.

Parikh, P. G.; Nagel, A. L.

1990-01-01

231

Laminar Soot Processes Experiment Shedding Light on Flame Radiation  

NASA Technical Reports Server (NTRS)

The Laminar Soot Processes (LSP) experiment investigated soot processes in nonturbulent, round gas jet diffusion flames in still air. The soot processes within these flames are relevant to practical combustion in aircraft propulsion systems, diesel engines, and furnaces. However, for the LSP experiment, the flames were slowed and spread out to allow measurements that are not tractable for practical, Earth-bound flames.

Urban, David L.

1998-01-01

232

Electrostatic quadrupole focused particle accelerating assembly with laminar flow beam  

DOEpatents

A charged particle accelerating assembly provided with a predetermined ratio of parametric structural characteristics and with related operating voltages applied to each of its linearly spaced focusing and accelerating quadrupoles, thereby to maintain a particle beam traversing the electrostatic fields of the quadrupoles in the assembly in an essentially laminar flow throughout the assembly.

Maschke, Alfred W. (East Moriches, NY)

1985-01-01

233

A bypass wake induced laminar\\/turbulent transition  

Microsoft Academic Search

The process of laminar to turbulent transition induced by a von Karman vortex street wake, was studied for the case of a flat plate boundary layer. The boundary layer developed under zero pressure gradient conditions. The vortex street was generated by a cylinder positioned in the free stream. An X-type hot-wire probe located in the boundary layer, measured the streamwise

N. K. Kyriakides; E. G. Kastrinakis; S. G. Nychas; A. Goulas

1999-01-01

234

Multiple paths to subharmonic laminar breakdown in a boundary layer  

NASA Technical Reports Server (NTRS)

Numerical simulations demonstrate that laminar breakdown in a boundary layer induced by the secondary instability of two-dimensional Tollmien-Schlichting waves to three-dimensional subharmonic disturbances need not take the conventional lambda vortex/high-shear layer path.

Zang, Thomas A.; Hussaini, M. Yousuff

1989-01-01

235

FORMATION OF ROLL WAVES IN LAMINAR SHEET FLOW  

E-print Network

functions of the Froude number #12;I. INTRODUCTION Sheet flow is classified as "wide" open channel flow because channel walls do not affect the flow pattern. Wide open channel flow exists when the ratioFORMATION OF ROLL WAVES IN LAMINAR SHEET FLOW by Pierre Y. Julien and David M. Hartley January 1985

Julien, Pierre Y.

236

The ignition of methanol droplets in a laminar convective environment  

Microsoft Academic Search

Numerical simulations of the ignition of methanol droplets in a laminar convective environment are performed using detailed reaction mechanisms and detailed transport models. The flow velocities of the forced convection ranges from 0.01 up to 5 m\\/s, whereas the ambient gas temperature is varied between 1300 and 1500 K. The ignition delay time of a single droplet is found to

R. Stauch; U. Maas

2008-01-01

237

Self-pumping suction/propulsion for laminar flow bodies  

NASA Astrophysics Data System (ADS)

An analysis is presented to investigate the feasibility of a self-pumping suction system for a very low drag suction laminar flow control (SLFC) underwater test body. The nose and afterbody of a torpedo-like body are contoured such that a prominent low-pressure region in the aft part of the body can serve as a suction pump to suck the boundary layer fluid through the circumferential surface-slots and thus laminarize the entire body length forward of the aft low-pressure peak. The results indicate that it is feasible to laminarize a test body in this fashion at a design speed, such as 40 knots; but that the laminarization of a particular configuration is limited to a band of speeds at and near the design speed. If an SLFC test body with a wide range of speed capability is desired, then a controllable-speed suction pump and controllable suction distribution along the body are indicated. The analysis includes a suction system design calculation example and should be a useful reference for future development of undersea SLFC vehicles.

Rogers, K. H.; King, D. A.

1984-06-01

238

Characteristics of Laminar Vortex Ring - Diffusion Flame Interaction  

Microsoft Academic Search

Direct numerical simulation (DNS) is performed to study the interaction between a laminar vortex ring and a diffusion flame. The compressible form of the Navier-Stokes equations are solved together with energy and species equations. The diffusion flame is generated by a `spark' and is implemented as initial condition for the simulations. A single-step second order irreversible Arrhenius type reaction is

C. Safta; C. K. Madnia

2000-01-01

239

Numerical Simulation of an Enclosed Laminar Jet Diffusion Flame in Microgravity Environment: Comparison with ELF Data  

NASA Technical Reports Server (NTRS)

Enclosed diffusion flames are commonly found in practical combustion systems, such as the power-plant combustor, gas turbine combustor, and jet engine after-burner. In these systems, fuel is injected into a duct with a co-flowing or cross-flowing air stream. The diffusion flame is found at the surface where the fuel jet and oxygen meet, react, and consume each other. In combustors, this flame is anchored at the burner (i.e., fuel jet inlet) unless adverse conditions cause the flame to lift off or blow out. Investigations of burner stability study the lift off, reattachment, and blow out of the flame. Flame stability is strongly dependent on the fuel jet velocity. When the fuel jet velocity is sufficiently low, the diffusion flame anchors at the burner rim. When the fuel jet velocity is increased, the flame base gradually moves downstream. However, when the fuel jet velocity increases beyond a critical value, the flame base abruptly jumps downstream. When this "jump" occurs, the flame is said to have reached its lift-off condition and the critical fuel jet velocity is called the lift-off velocity. While lifted, the flame is not attached to the burner and it appears to float in mid-air. Flow conditions are such that the flame cannot be maintained at the burner rim despite the presence of both fuel and oxygen. When the fuel jet velocity is further increased, the flame will eventually extinguish at its blowout condition. In contrast, if the fuel jet velocity of a lifted flame is reduced, the flame base moves upstream and abruptly returns to anchor at the burner rim. The fuel jet velocity at reattachment can be much lower than that at lift off, illustrating the hysteresis effect present in flame stability. Although there have been numerous studies of flame stability, the controlling mechanisms are not well understood. This uncertainty is described by Pitts in his review of various competing theories of lift off and blow out in turbulent jet diffusion flames. There has been some research on the stability of laminar flames, but most studies have focused on turbulent flames. It is also well known that the airflow around the fuel jet can significantly alter the lift off, reattachment and blow out of the jet diffusion flame. Buoyant convection is sufficiently strong in 1-g flames that it can dominate the flow-field, even at the burner rim. In normal-gravity testing, it is very difficult to delineate the effects of the forced airflow from those of the buoyancy-induced flow. Comparison of normal-gravity and microgravity flames provides clear indication of the influence of forced and buoyant flows on the flame stability. The overall goal of the Enclosed Laminar Flames (ELF) investigation (STS-87/USMP-4 Space Shuttle mission, November to December 1997) is to improve our understanding of the effects of buoyant convection on the structure and stability of co-flow diffusion flame, e.g., see http://zeta.lerc.nasa.gov/expr/elf.htm. The ELF hardware meets the experiment hardware limit of the 35-liter interior volume of the glovebox working area, and the 180x220-mm dimensions of the main door. The ELF experiment module is a miniature, fan-driven wind tunnel, equipped with a gas supply system. A 1.5-mm diameter nozzle is located on the duct's flow axis. The cross section of the duct is nominally a 76-mm square with rounded corners. The forced air velocity can be varied from about 0.2 to 0.9 m/s. The fuel flow can be set as high as 3 std. cubic centimeter (cc) per second, which corresponds to a nozzle exit velocity of up to 1.70 m/s. The ELF hardware and experimental procedure are discussed in detail in Brooker et al. The 1-g test results are repeated in several experiments following the STS-87 Mission. The ELF study is also relevant to practical systems because the momentum-dominated behavior of turbulent flames can be achieved in laminar flames in microgravity. The specific objectives of this paper are to evaluate the use reduced model for simulation of flame lift-off and blowout.

Jia, Kezhong; Venuturumilli, Rajasekhar; Ryan, Brandon J.; Chen, Lea-Der

2001-01-01

240

Wing laminar boundary layer in the presence of a propeller slipstream  

NASA Technical Reports Server (NTRS)

The effects of a propeller slipstream on the wing laminar boundary layer are being investigated. Hot-wire velocity sensor measurements have been performed in flight and in a wind tunnel. It is shown that the boundary layer cycles between a laminar state and a turbulent state at the propeller blade passage rate. The cyclic length of the turbulent state increases with decreasing laminar stability. Analyses of the time varying velocity profiles show the turbulent state to lie in a transition region between fully laminar and fully turbulent. The observed cyclic boundary layer has characteristics similar to relaminarizing flow and laminar flow with external turbulence.

Miley, S. J.; Howard, R. M.; Holmes, B. J.

1986-01-01

241

Detection of airflow limitation using a handheld spirometer in a primary care setting  

PubMed Central

Background and objective Early diagnosis of chronic obstructive pulmonary disease (COPD) in primary care settings is difficult to achieve chiefly due to lack of availability of spirometry. This study estimated the prevalence of airflow limitation among chronic smokers using a handheld spirometer in this setting. Methods This is a cross-sectional study performed on consecutive patients who were ?40 years old with ?10 pack-years smoking history. Face-to-face interviews were carried out to obtain demographic data and relevant information. Handheld spirometry was performed according to a standard protocol using the COPd-6 device (Model 4000, Vitalograph, Ennis, Ireland) in addition to standard spirometry. Airflow limitation was defined as ratio of forced expiratory volume in 1 s (FEV1)/forced expiratory volume in 6 s <0.75 (COPd-6) or FEV1/forced vital capacity <0.7. Multiple logistic regression analyses were used to determine predictors of airflow limitation. Results A total of 416 patients were recruited with mean age of 53 years old. The prevalence of airflow limitation was 10.6% (n = 44) with COPd-6 versus 6% as gauged using standard spirometry. Risk factors for airflow limitation were age >65 years (odds ratio (OR) 3.732 95% confidence interval (CI): 1.100–1.280), a history of ‘bad health’ (OR 2.524, 95% CI: 1.037–6.142) and low to normal body mass index (OR 2.914, 95% CI: 1.191–7.190). Conclusions In a primary care setting, handheld spirometry (COPd-6) found a prevalence of airflow limitation of ?10% in smokers. Patients were older, not overweight and had an ill-defined history of health problems. SUMMARY AT A GLANCE Prevalence of COPD is unknown in Malaysia. The prevalence of COPD using a handheld spirometer (COPd-6TM) was 10.6% versus 6% as gauged using standard spirometry. Predictors of COPD were older age, lower BMI and a history of ‘bad health’. Case-finding for COPD should be targeted in this special population. PMID:24708063

Ching, Siew-Mooi; Pang, Yong-Kek; Price, David; Cheong, Ai-Theng; Lee, Ping-Yein; Irmi, Ismail; Faezah, Hassan; Ruhaini, Ismail; Chia, Yook-Chin

2014-01-01

242

Unique airflow visualization techniques for the design and validation of above-plenum data center CFD models  

E-print Network

One cause for the substantial amount of energy used for data center cooling is poor airflow effects such as hot-aisle to cold-aisle air recirculation. To correct these and to investigate innovative designs that will notably ...

Lloyd, Michael David, S.M. Massachusetts Institute of Technology

2010-01-01

243

The coupling influence of airflow and temperature on the wall-wetted fuel film distribution  

SciTech Connect

The coupling influence of airflow and temperature on the two-dimensional distribution of the film resulted from fuel spray impinging on a horizontal flat wall was studied with experiments. The horizontal airflow direction was perpendicular to the vertical axis of the injection spray. The results show that, as air velocity increases, the film shape turns from a circle to an oblong. As wall temperature increases, the film area shrinks. Film thickness decreases as wall temperature or air velocity increases. The boiling point of the fuel is an important temperature to affect the film area and the film thickness. Film center moves more far away in the downstream direction as air velocity increases. For a certain air velocity, film center moves less far away as wall temperature increases. (author)

Cheng, Yong-sheng [School of Aeronautics and Astronautics, Shanghai Jiao Tong University, Shanghai 200240 (China); Deng, Kangyao; Li, Tao [Key Laboratory for Power Machinery and Engineering of Ministry of Education, Shanghai Jiao Tong University, Shanghai 200240 (China)

2010-02-15

244

Stabilization of liquid hydrocarbon fuel combustion by using a programmable microwave discharge in a subsonic airflow  

SciTech Connect

Under conditions of a programmable discharge (a surface microwave discharge combined with a dc discharge), plasma-enhanced combustion of alcohol injected into a subsonic (M = 0.3-0.9) airflow in the drop (spray) phase is stabilized. It is shown that the appearance of the discharge, its current-voltage characteristic, the emission spectrum, the total emission intensity, the heat flux, the electron density, the hydroxyl emission intensity, and the time dependences of the discharge current and especially discharge voltage change substantially during the transition from the airflow discharge to stabilized combustion of the liquid hydrocarbon fuel. After combustion stabilization, more than 80% of liquid alcohol can burn out, depending on the input power, and the flame temperature reaches {approx}2000 K.

Kopyl, P. V.; Surkont, O. S.; Shibkov, V. M.; Shibkova, L. V. [Moscow State University, Faculty of Physics (Russian Federation)

2012-06-15

245

Mechanical Design of a Performance Test Rig for the Turbine Air-Flow Task (TAFT)  

NASA Technical Reports Server (NTRS)

To support development of the Boeing-Rocketdyne RS84 rocket engine, a full-flow, reaction turbine geometry was integrated into the NASA-MSFC turbine air-flow test facility. A mechanical design was generated which minimized the amount of new hardware while incorporating all test and instrumentation requirements. This paper provides details of the mechanical design for this Turbine Air-Flow Task (TAFT) test rig. The mechanical design process utilized for this task included the following basic stages: Conceptual Design. Preliminary Design. Detailed Design. Baseline of Design (including Configuration Control and Drawing Revision). Fabrication. Assembly. During the design process, many lessons were learned that should benefit future test rig design projects. Of primary importance are well-defined requirements early in the design process, a thorough detailed design package, and effective communication with both the customer and the fabrication contractors.

Forbes, John C.; Xenofos, George D.; Farrow, John L.; Tyler, Tom; Williams, Robert; Sargent, Scott; Moharos, Jozsef

2004-01-01

246

Characterizing Indoor Airflow and Pollutant Transport using Simulation Modeling for Prototypical Buildings. I. Office Buildings  

SciTech Connect

This paper describes the first efforts at developing a set of prototypical buildings defined to capture the key features affecting airflow and pollutant transport in buildings. These buildings will be used to model airflow and pollutant transport for emergency response scenarios when limited site-specific information is available and immediate decisions must be made, and to better understand key features of buildings controlling occupant exposures to indoor pollutant sources. This paper presents an example of this approach for a prototypical intermediate-sized, open style, commercial building. Interzonal transport due to a short-term source release, e.g., accidental chemical spill, in the bottom and the upper floors is predicted and corresponding HVAC system operation effects and potential responses are considered. Three-hour average exposure estimates are used to compare effects of source location and HVAC operation.

Sohn, M.D.; Daisey, J.M.; Feustel, H.E.

1999-06-01

247

Airflow Simulation and Particle Deposition in a 3D Rat Lung Model  

NASA Astrophysics Data System (ADS)

Knowledge of the fate of aerosols in the lung is needed to understand the efficiency of inhaled drug therapy. Invasive animal experiments and imaging allows for detailed quantitative comparison with computational modeling. In this study we built a three-dimensional (3D) airway tree model using rat magnetic resonance images. A custom 3D finite element solver was used to obtain animal specific velocities and pressures. Inlet boundary conditions were chosen to match a previous rat ventilation experiment and resistance outlet boundary conditions were selected to match a desired airflow split based on uniform ventilation. The Maxey-Riley particle equations were solved using Lagrangian particle tracking methods with realistic aerosol particle dimensions and density. The particle dynamics were validated using analytical solutions in idealized geometries. The impact of the choice of outlet boundary conditions for airflow simulations is quantified and aerosol particle deposition and distribution within the lung lobes are explored.

Oakes, Jessica; Shadden, Shawn; Darquenne, Chantal; Marsden, Alison

2010-11-01

248

Influence of airflow rate and substrate nature on heterogeneous struvite precipitation.  

PubMed

In wastewater treatment plants a hard scale consisting of struvite crystals can be formed, in pipes and recirculation pumps, during anaerobic digestion of wastewater. This study was conducted to evaluate the effect of airflow rate and substrate nature on nucleation type, induction period and supersaturation coefficient during struvite precipitation. A crystallization reactor similar to that designed for calcium carbonate precipitation was used. The pH of synthetic wastewater solution was increased by air bubbling. Experimental results indicated that the airflow increased heterogeneous precipitation of struvite. The susceptibility to scale formation was more important on polyamide and polyvinyl chloride than on stainless steel. In all cases, X-ray diffraction and infrared spectroscopy showed that the precipitated solid phase was solely struvite. No difference in crystal morphology was observed. However, at similar experimental conditions, the particle size of struvite was higher for stainless-steel material than that for plastic materials. PMID:19213469

Saidou, H; Ben Moussa, S; Ben Amor, M

2009-01-01

249

Two models of high frequency chest compression therapy: interaction of jacket pressure and mouth airflow.  

PubMed

High frequency chest compression (HFCC) therapy assists clearing the secretions in the lung. This paper presents two mathematical models: 1) HFCC jacket function model (JFM) and 2) respiratory function model (RFM). JFM predicts the variation of the jacket pressure (Pj) from the respiratory pattern of mouth airflow (Fm). RFM predicts the HFCC induced mouth airflow (Fm) from the HFCC pulse pressures at the jacket (Pj). Fm and Pj were measured from a healthy subject during HFCC therapy. JFM, which was implemented with 2nd order system using prediction error method, shows the existence of breathing pattern at Pj. RFM, which was implemented with amplitude modulation technique, shows how the HFCC pulses affects to the Fm. JFM calculations match 78% of the measured respiratory pattern of Pj>. RFM calculations match 90% of measured HFCC induced Fm. These models can be used to test new breathing patterns before designing studies on patients having chronic obstructive pulmonary diseases. PMID:18002939

Lee, Yong Wan; Lee, Jongwon; Warwick, Warren J

2007-01-01

250

Design, fabrication, and control of MEMS-based actuator arrays for air-flow distributed micromanipulation  

Microsoft Academic Search

This paper reports the design, fabrication and control of arrayed microelectromechanical systems (MEMS)-based actuators for distributed micromanipulation by generation and control of an air-flow force field. The authors present an original design of pneumatic microactuator, improving reliability and durability of a distributed planar micromanipulator described in the previous study. The fabrication process is based on silicon-on-insulator (SOI) wafer and HF

Yamato Fukuta; Yves-Andre Chapuis; Yoshio Mita; Hiroyuki Fujita

2006-01-01

251

Laboratory determination of compost physical parameters for modeling of airflow characteristics  

Microsoft Academic Search

Physical parameters of 12 co-compost cover materials were experimentally determined and predicted variations in airflow characteristics were evaluated under varying moisture contents. Predicted air-filled porosity showed high correlation with measured air-filled porosity, facilitating development of a reliable model of air-filled porosity that makes it possible to predict the effect of varying moisture content and compost bed height on air-filled porosity

H. K. Ahn; T. L. Richard; T. D. Glanville

2008-01-01

252

An experimental study on transverse hydrogen gas injection into mach 1.8 airflow channel  

Microsoft Academic Search

Experimental results from a series of injection tests of pressurized H2, N2 gases into Mach 1.8 airflows between parallel channel walls through a flush-mounted circular sonic opening have been presented.\\u000a Schlieren pictures revealed complex interaction flow features including the occurrence of bow\\/separation shock waves due to\\u000a the injection as well as the barrel shock\\/Mach disc structure inside the injected gas

T. Nagashima; H. Itoh; S. Noguchi; Y. Kotani

1997-01-01

253

Payload bay atmospheric vent airflow testing at the Vibration and Acoustic Test Facility  

NASA Technical Reports Server (NTRS)

Several concerns related to venting the Space Shuttle Orbiter payload bay during launch led to laboratory experiments with a flight-type vent box installed in the wall of a subsonic wind tunnel. This report describes the test setups and procedures used to acquire data for characterization of airflow through the vent box and acoustic tones radiated from the vent-box cavity. A flexible boundary-layer spoiler which reduced the vent-tone amplitude is described.

Johnston, James D., Jr.

1988-01-01

254

Asymmetric surface dielectric barrier discharge in air at atmospheric pressure: electrical properties and induced airflow characteristics  

Microsoft Academic Search

The electrical properties of an asymmetric surface dielectric barrier discharge in atmospheric air have been investigated experimentally. The discharge is used for airflow production close to the dielectric surface, and the time-averaged flow velocity spatial profiles have been measured. Velocities of up to 3.5 m s-1 at heights of 1-2 mm are reached when filamentary discharges with current peaks up

Jérôme Pons; Eric Moreau; Gérard Touchard

2005-01-01

255

Combined simulation of airflow, radiation and moisture transport for heat release from a human body  

Microsoft Academic Search

This paper described a combined numerical simulation method of airflow, thermal radiation and moisture transport for predicting heat release from a human body. A human thermo-physiological model was also included to examine the sensible and latent heat transfer from the human body. Flow, temperature and moisture fields were investigated with three-dimensional Computational Fluid Dynamics (CFD). We used a low-Reynolds-number type

Shuzo Murakami; Shinsuke Kato; Jie Zeng

2000-01-01

256

Studies on reduction of yarn hairiness by nozzles in ring spinning and winding by airflow simulation  

Microsoft Academic Search

Reduction of yarn hairiness by nozzles in ring spinning and winding is a new approach. Simulation of the airflow pattern inside\\u000a the nozzles provides useful information about actual mechanism of hairiness reduction. The swirling air current inside the\\u000a nozzles is capable of wrapping the protruding hairs around the yarn body, thereby reducing yarn hairiness. Since production\\u000a rate of winding is

R. S. Rengasamy; Asis Patnaik; Hemant Punekar

2006-01-01

257

Indices of Upper Airway Obstruction in Patients with Simultaneous Chronic Airflow Limitation  

Microsoft Academic Search

In patients with chronic airflow limitation (CAL), the detection of upper airway obstruction (UAO) by analysis of forced flows can be difficult due to the masking of conventional UAO indices. We analyzed five indices: maximum inspiratory flow at 50% of forced vital capacity (FIF50), the ratio of maximum expiratory to inspiratory flow at 50% of forced vital capacity (FEF50\\/FIF50), the

Eduardo García-Pachón; Pere Casan; Joaquín Sanchis

1994-01-01

258

Gyrotactic trapping in laminar and turbulent Kolmogorov flow  

NASA Astrophysics Data System (ADS)

Phytoplankton patchiness, namely the heterogeneous distribution of microalgae over multiple spatial scales, dramatically impacts marine ecology. A spectacular example of such heterogeneity occurs in thin phytoplankton layers (TPLs), where large numbers of photosynthetic microorganisms are found within a small depth interval. Some species of motile phytoplankton can form TPLs by gyrotactic trapping due to the interplay of their particular swimming style (directed motion biased against gravity) and the transport by a flow with shear along the direction of gravity. Here we consider gyrotactic swimmers in numerical simulations of the Kolmogorov shear flow, both in laminar and turbulent regimes. In the laminar case, we show that the swimmer motion is integrable and the formation of TPLs can be fully characterized by means of dynamical systems tools. We then study the effects of rotational Brownian motion or turbulent fluctuations (appearing when the Reynolds number is large enough) on TPLs. In both cases, we show that TPLs become transient, and we characterize their persistence.

Santamaria, Francesco; De Lillo, Filippo; Cencini, Massimo; Boffetta, Guido

2014-11-01

259

Nature of laminar-turbulence intermittency in shear flows.  

PubMed

In pipe, channel, and boundary layer flows turbulence first occurs intermittently in space and time: at moderate Reynolds numbers domains of disordered turbulent motion are separated by quiescent laminar regions. Based on direct numerical simulations of pipe flow we argue here that the spatial intermittency has its origin in a nearest neighbor interaction between turbulent regions. We further show that in this regime turbulent flows are intrinsically intermittent with a well-defined equilibrium turbulent fraction but without ever assuming a steady pattern. This transition scenario is analogous to that found in simple models such as coupled map lattices. The scaling observed implies that laminar intermissions of the turbulent flow will persist to arbitrarily large Reynolds numbers. PMID:23848777

Avila, M; Hof, B

2013-06-01

260

Laminar/turbulent oscillating flow in circular pipes  

NASA Technical Reports Server (NTRS)

A two-dimensional oscillating flow analysis was conducted simulating the gas flow inside Stirling engine heat exchangers. Both laminar and turbulent oscillating pipe flow were investigated numerically for Re(max) = 1920 (Va = 80), 10,800 (Va = 272), 19,300 (Va = 272), and 60,800 (Va = 126). The results are compared with experimental results of previous investigators. Predictions of the flow regime are also checked by comparing velocity amplitudes and phase difference with those from laminar theory and quasi-steady profile. A high Reynolds number k-epsilon turbulence model was used for turbulent oscillating pipe flow. Finally, the performance of the k-epsilon model was evaluated to explore the applicability of quasi-steady turbulent models to unsteady oscillating flow analysis.

Ahn, Kyung H.; Ibrahim, Mounir B.

1992-01-01

261

Nonlinear spectral dynamics of hypersonic laminar boundary layer flow  

NASA Astrophysics Data System (ADS)

The nonlinear interactions of the instability modes in a hypersonic laminar boundary layer undergoing natural transition are examined using bispectral analysis. The data are from an experiment of a boundary layer flow on a cooled-wall cone in a low-level free-stream disturbance hypersonic wind tunnel, and thus, the bispectral measurements are a good representation of the natural transition processes. The bispectral analysis shows that in the initial stages of transition the dominant nonlinear interaction is forcing by the fundamental to generate a harmonic. Subsequently, mutual forcing of the fundamental and harmonic yield a second harmonic. Difference interactions within the band of unstable disturbances centered on the fundamental and harmonic also generate a low frequency nonlinear interaction. At high amplitudes of the fundamental and harmonic a nonlinear interaction characterized by a low frequency modulation of the fundamental and harmonic then follows. This nonlinear interaction is then the most dominant and precedes the breakdown of the laminar flow.

Chokani, Ndaona

1999-12-01

262

Correlations of laminar combustion data for alternative SI engine fuels  

SciTech Connect

Most of the spark ignition engine cycle simulations use turbulent burning models which require a knowledge of laminar burning velocity of the fuel-air mixture as a function of mixture strength, unburned mixture temperature and pressure. Burning velocity data of different alternative spark ignition engine fuels obtained by various workers have been compared and critically evaluated. Empirical and semi-empirical correlations, suitable for cycle simulation studies, are presented for laminar burning velocity as a function of mixture strength, unburned mixture temperature, pressure, and residual gas fraction. Fuels considered include ethanol, methanol, alcohol/water blends, isooctane/alcohol blends, propane and isooctane. Experimental data obtained by the present author constitute the major part of the data used in correlations. Published data of other workers and the predictions of theoretical thermo-kinetic models have also been considered in correlations.

Gulder, O.L.

1984-01-01

263

Preliminary aerodynamic design considerations for advanced laminar flow aircraft configurations  

NASA Technical Reports Server (NTRS)

Modern composite manufacturing methods have provided the opportunity for smooth surfaces that can sustain large regions of natural laminar flow (NLF) boundary layer behavior and have stimulated interest in developing advanced NLF airfoils and improved aircraft designs. Some of the preliminary results obtained in exploratory research investigations on advanced aircraft configurations at the NASA Langley Research Center are discussed. Results of the initial studies have shown that the aerodynamic effects of configuration variables such as canard/wing arrangements, airfoils, and pusher-type and tractor-type propeller installations can be particularly significant at high angles of attack. Flow field interactions between aircraft components were shown to produce undesirable aerodynamic effects on a wing behind a heavily loaded canard, and the use of properly designed wing leading-edge modifications, such as a leading-edge droop, offset the undesirable aerodynamic effects by delaying wing stall and providing increased stall/spin resistance with minimum degradation of laminar flow behavior.

Johnson, Joseph L., Jr.; Yip, Long P.; Jordan, Frank L., Jr.

1986-01-01

264

Periodontitis is related to lung volumes and airflow limitation: a cross-sectional study.  

PubMed

This study aimed to assess the potential association of periodontal diseases with lung volumes and airflow limitation in a general adult population. Based on a representative population sample of the Study of Health in Pomerania (SHIP), 1463 subjects aged 25-86 years were included. Periodontal status was assessed by clinical attachment loss (CAL), probing depth and number of missing teeth. Lung function was measured using spirometry, body plethysmography and diffusing capacity of the lung for carbon monoxide. Linear regression models using fractional polynomials were used to assess associations between periodontal disease and lung function. Fibrinogen and high-sensitivity C-reactive protein (hs-CRP) were evaluated as potential intermediate factors. After full adjustment for potential confounders mean CAL was significantly associated with variables of mobile dynamic and static lung volumes, airflow limitation and hyperinflation (p<0.05). Including fibrinogen and hs-CRP did not change coefficients of mean CAL; associations remained statistically significant. Mean CAL was not associated with total lung capacity and diffusing capacity of the lung for carbon monoxide. Associations were confirmed for mean probing depth, extent measures of CAL/probing depth and number of missing teeth. Periodontal disease was significantly associated with reduced lung volumes and airflow limitation in this general adult population sample. Systemic inflammation did not provide a mechanism linking both diseases. PMID:23222882

Holtfreter, Birte; Richter, Stefanie; Kocher, Thomas; Dörr, Marcus; Völzke, Henry; Ittermann, Till; Obst, Anne; Schäper, Christoph; John, Ulrich; Meisel, Peter; Grotevendt, Anne; Felix, Stephan B; Ewert, Ralf; Gläser, Sven

2013-12-01

265

COMIS -- an international multizone air-flow and contaminant transport model  

SciTech Connect

A number of interzonal models have been developed to calculate air flows and pollutant transport mechanisms in both single and multizone buildings. A recent development in multizone air-flow modeling, the COMIS model, has a number of capabilities that go beyond previous models, much as COMIS can be used as either a stand-alone air-flow model with input and output features or as an infiltration module for thermal building simulation programs. COMIS was designed during a 12 month workshop at Lawrence Berkeley National Laboratory (LBNL) in 1988-89. In 1990, the Executive Committee of the International Energy Agency`s Energy Conservation in Buildings and Community Systems program created a working group on multizone air-flow modeling, which continued work on COMIS. The group`s objectives were to study physical phenomena causing air flow and pollutant (e.g., moisture) transport in multizone buildings, develop numerical modules to be integrated in the previously designed multizone air flow modeling system, and evaluate the computer code. The working group supported by nine nations, officially finished in late 1997 with the release of IISiBat/COMIS 3.0, which contains the documented simulation program COMIS, the user interface IISiBat, and reports describing the evaluation exercise.

Feustel, H.E.

1998-08-01

266

Comparison of Airflows in Weibel-based and CT-based Human Lung Geometries  

NASA Astrophysics Data System (ADS)

The need for patient specific lung geometry for study of pulmonary air flow and drug delivery has been emphasized recently due to the complexity of individual airway tree geometry. The objective of this paper is to assess the notion of patient specific geometry by comparing airflows in an idealized Weibel-based lung model and two realistic human lung geometries. The Weibel-based model is composed of cylinders of differing diameters for various branching and has been used extensively for modeling airflow in lungs. Here a 4-generation Weibel model is considered. The realistic lung geometries are segmented and reconstructured from computerized tomography (CT) images as part of an effort to build a normative atlas (NIH HL-04368) documenting airway geometry over 4 decades of age in healthy and disease-state adult humans. The custom developed Taylor-Galerkin finite element code, which solves the incompressible Navier-Stokes equations, is applied to simulate airflows in these lung geometries. The velocity wave form recorded from a mechanical ventilator is adopted as the inlet pulsatile boundary condition. At the outlets, both the pressure and outflow boundary conditions are applied and compared. The counter-rotating vortices are observed in the Weibel model during both the inspiratory and expiratory cycles, being consistent with previous studies. The flow structures in the CT-based models are much more complicated and counter-rotating vortices are only evident in some regions.

Lin, Ching-Long; Hoffman, Eric A.

2004-11-01

267

On intra- and intersubject variabilities of airflow in the human lungs  

PubMed Central

The effects of intra- and intersubject variabilities in airway geometry on airflow in the human lungs are investigated by large eddy simulation. The airway models of two human subjects consisting of extra- and intrathoracic airways are reconstructed from CT images. For intrasubject study, airflows at two inspiratory flow rates are simulated on the airway geometries of the same subject with four different levels of truncation. These airway models are the original complete geometry and three geometries obtained by truncating the original one at the subglottis, the supraglottis, and the laryngopharynx, respectively. A comparison of the airflows in the complete geometry model shows that the characteristics of the turbulent laryngeal jet in the trachea are similar regardless of Reynolds number in terms of mean velocities, turbulence statistics, coherent structures, and pressure distribution. The truncated airway models, however, do not produce the similar flow structures observed in the complete geometry. An improved inlet boundary condition is then proposed for the airway model truncated at the laryngopharynx to improve the accuracy of solution. The new boundary condition significantly improves the mean flow. The spectral analysis shows that turbulent characteristics are captured downstream away from the glottis. For intersubject study, although the overall flow characteristics are similar, two morphological factors are found to significantly affect the flows between subjects. These are the constriction ratio of the glottis with respect to the trachea and the curvature and shape of the airways. PMID:19901999

Choi, Jiwoong; Tawhai, Merryn H.; Hoffman, Eric A.; Lin, Ching-Long

2009-01-01

268

The excitation of unstable perturbations in a laminar friction layer  

NASA Technical Reports Server (NTRS)

With the aid of the method of small oscillations which was used successfully in the investigation of the stability of laminar velocity distributions in the presence of two-dimensional perturbations, the excitation of the unstable perturbations for the Hartree velocity distributions occurring in plane boundary-layer flow for decreasing and increasing pressure is calculated as a supplement to a former report. The results of this investigation are to make a contribution toward calculation of the transition point on cylindrical bodies.

Pretsch, Joachim

1952-01-01

269

Advanced Surface Laminar Circuit using new composite materials  

Microsoft Academic Search

This paper introduces a newly developed Advanced Surface Laminar Circuit (Adv-SLC) packaging technology, which utilizes new composite materials. Adv-SLC is a buildup substrate technology designed to satisfy the requirements of the most advanced semiconductor chips. We have developed a new dielectric material that is a build-up layer composed of two different materials. We also used a new material for the

Katsura Hayashi; Kimihiro Yamanaka; Kaoru Kobayashi; Yoshihiro Hosoi; Masahiro Fukui

2010-01-01

270

Advanced Surface Laminar Circuits Using Newly Developed Resins  

Microsoft Academic Search

This paper introduces a newly developed advanced surface laminar circuit (Adv-SLC) packaging technology, which utilizes new composite materials. Adv-SLC is a build-up substrate technology designed to fulfill the requirements of the most advanced semiconductor chips. Our new dielectric material is a build-up layer composed of two different materials. We also used a new material for the core substrate, composed of

Katsura Hayashi; Kimihiro Yamanaka; Kaoru Kobayashi; Yoshihiro Hosoi; Masahiro Fukui

2011-01-01

271

Flame Shapes of Nonbuoyant Laminar Jet Diffusion Flames. Appendix K  

NASA Technical Reports Server (NTRS)

The shapes (flame-sheet and luminous-flame boundaries) of steady nonbuoyant round hydrocarbon-fueled laminar-jet diffusion flames in still and coflowing air were studied both experimentally and theoretically. Flame-sheet shapes were measured from photographs using a CH optical filter to distinguish flame-sheet boundaries in the presence of blue C02 and OH emissions and yellow continuum radiation from soot. Present experimental conditions included acetylene-, methane-, propane-, and ethylene-fueled flames having initial reactant temperatures of 300 K, ambient pressures of 4-50 kPa, jet exit Reynolds number of 3-54, initial air/fuel velocity ratios of 0-9 and luminous flame lengths of 5-55 mm; earlier measurements for propylene- and 1,3-butadiene-fueled flames for similar conditions were considered as well. Nonbuoyant flames in still air were observed at micro-gravity conditions; essentially nonbuoyant flames in coflowing air were observed at small pressures to control effects of buoyancy. Predictions of luminous flame boundaries from soot luminosity were limited to laminar smoke-point conditions, whereas predictions of flame-sheet boundaries ranged from soot-free to smoke-point conditions. Flame-shape predictions were based on simplified analyses using the boundary layer approximations along with empirical parameters to distinguish flame-sheet and luminous-flame (at the laminar smoke point) boundaries. The comparison between measurements and predictions was remarkably good and showed that both flame-sheet and luminous-flame lengths are primarily controlled by fuel flow rates with lengths in coflowing air approaching 2/3 lengths in still air as coflowing air velocities are increased. Finally, luminous flame lengths at laminar smoke-point conditions were roughly twice as long as flame-sheet lengths at comparable conditions due to the presence of luminous soot particles in the fuel-lean region of the flames.

Xu, F.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

2000-01-01

272

Flame height measurement of laminar inverse diffusion flames  

Microsoft Academic Search

Flame heights of co-flowing cylindrical ethylene-air and methane-air laminar inverse diffusion flames were measured. The luminous flame height was found to be greater than the height of the reaction zone determined by planar laser-induced fluorescence (PLIF) of hydroxyl radicals (OH) because of luminous soot above the reaction zone. However, the location of the peak luminous signals along the centerline agreed

Christopher R. Shaddix; Timothy C. Williams; Linda Gail Blevins; Mark A. Mikofski

2005-01-01

273

Flame height measurement of laminar inverse diffusion flames  

Microsoft Academic Search

Flame heights of co-flowing cylindrical ethylene-air and methane-air laminar inverse diffusion flames were measured. The luminous flame height was found to be greater than the height of the reaction zone determined by planar laser-induced fluorescence (PLIF) of hydroxyl radicals (OH) because of luminous soot above the reaction zone. However, the location of the peak luminous signals along the centerline agreed

Mark A. Mikofski; Timothy C. Williams; Christopher R. Shaddix; Linda G. Blevins

2006-01-01

274

Flame height measurement of laminar inverse diffusion flames  

Microsoft Academic Search

Flame heights of co-flowing cylindrical ethylene–air and methane–air laminar inverse diffusion flames were measured. The luminous flame height was found to be greater than the height of the reaction zone determined by planar laser-induced fluorescence (PLIF) of hydroxyl radicals (OH) because of luminous soot above the reaction zone. However, the location of the peak luminous signals along the centerline agreed

Mark A. Mikofski; Timothy C. Williams; Christopher R. Shaddix; Linda G. Blevins

2006-01-01

275

Flame Shapes of Nonbuoyant Laminar Jet Diffusion Flames  

NASA Technical Reports Server (NTRS)

The shapes (flame-sheet and luminous-flame boundaries) of steady nonbuoyant round hydrocarbon-fueled laminar-jet diffusion flames in still and coflowing air were studied both experimentally and theoretically. Flame-sheet shapes were measured from photographs using a CH optical filter to distinguish flame-sheet boundaries in the presence of blue CO2 and OH emissions and yellow continuum radiation from soot. Present experimental conditions included acetylene-, methane-, propane-, and ethylene-fueled flames having initial reactant temperatures of 300 K, ambient pressures of 4-50 kPa, jet exit Reynolds number of 3-54, initial air/fuel velocity ratios of 0-9 and luminous flame lengths of 5-55 mm; earlier measurements for propylene- and 1,3-butadiene-fueled flames for similar conditions were considered as well. Nonbuoyant flames in still air were observed at micro-gravity conditions; essentially nonbuoyant flames in coflowing air were observed at small pressures to control effects of buoyancy. Predictions of luminous flame boundaries from soot luminosity were limited to laminar smokepoint conditions, whereas predictions of flame-sheet boundaries ranged from soot-free to smokepoint conditions. Flame-shape predictions were based on simplified analyses using the boundary layer approximations along with empirical parameters to distinguish flame-sheet and luminous flame (at the laminar smoke point) boundaries. The comparison between measurements and predictions was remarkably good and showed that both flame-sheet and luminous-flame lengths are primarily controlled by fuel flow rates with lengths in coflowing air approaching 2/3 lengths in still air as coflowing air velocities are increased. Finally, luminous flame lengths at laminar smoke-point conditions were roughly twice as long as flame-sheet lengths at comparable conditions due to the presence of luminous soot particles in the fuel-lean region of the flames.

Xu, F.; Dai, Z.; Faeth, G. M.; Urban, D. L. (Technical Monitor); Yuan, Z. G. (Technical Monitor)

2001-01-01

276

Laminar Flow Supersonic Wind Tunnel primary air injector  

NASA Technical Reports Server (NTRS)

This paper describes the requirements, design, and prototype testing of the flex-section and hinge seals for the Laminar Flow Supersonic Wind Tunnel Primary Injector. The supersonic atmospheric primary injector operates between Mach 1.8 and Mach 2.2 with mass-flow rates of 62 to 128 lbm/s providing the necessary pressure reduction to operate the tunnel in the desired Reynolds number (Re) range.

Smith, Brooke Edward

1993-01-01

277

Laminar flow efficiency of stratified chilled-water storage tanks  

Microsoft Academic Search

This paper presents results for the efficiency of a stratified chilled-water storage tank with one inlet and one outlet. Numerical solutions for the two-dimensional, unsteady, laminar flow during stably stratified tank filling are compared with a one-dimensional model involving only conductive heat transfer across the thermocline separating the entering cold water and the exiting warm water. This one-dimensional model represents

K. O. Homan; S. L. Soo

1998-01-01

278

Structure and Soot Formation Properties of Laminar Flames  

NASA Technical Reports Server (NTRS)

Soot formation within hydrocarbon-fueled flames is an important unresolved problem of combustion science for several reasons: soot emissions are responsible for more deaths than any other combustion-generated pollutant, thermal loads due to continuum radiation from soot limit the durability of combustors, thermal radiation from soot is mainly responsible for the growth and spread of unwanted fires, carbon monoxide emissions associated with soot emissions are responsible for most fire deaths, and limited understanding of soot processes in flames is a major impediment to the development of computational combustion. Motivated by these observations, soot processes within laminar premixed and nonpremixed (diffusion) flames are being studied during this investigation. The study is limited to laminar flames due to their experimental and computational tractability, noting the relevance of these results to practical flames through laminar flamelet concepts. Nonbuoyant flames are emphasized because buoyancy affects soot processes in laminar diffusion flames whereas effects of buoyancy are small for most practical flames. This study involves both ground- and space-based experiments, however, the following discussion will be limited to ground-based experiments because no space-based experiments were carried out during the report period. The objective of this work was to complete measurements in both premixed and nonpremixed flames in order to gain a better understanding of the structure of the soot-containing region and processes of soot nucleation and surface growth in these environments, with the latter information to be used to develop reliable ways of predicting soot properties in practical flames. The present discussion is brief, more details about the portions of the investigation considered here can be found in refs. 8-13.

El-Leathy, A. M.; Xu, F.; Faeth, G. M.

2001-01-01

279

Ground vibration test of the laminar flow control JStar airplane  

NASA Technical Reports Server (NTRS)

A ground vibration test was conducted on a Lockheed JetStar airplane that had been modified for the purpose of conducting laminar flow control experiments. The test was performed prior to initial flight flutter tests. Both sine-dwell and single-point-random excitation methods were used. The data presented include frequency response functions and a comparison of mode frequencies and mode shapes from both methods.

Kehoe, M. W.; Cazier, F. W., Jr.; Ellison, J. F.

1985-01-01

280

Laminar shocks in high power laser plasma interactions  

SciTech Connect

We propose a theory to describe laminar ion sound structures in a collisionless plasma. Reflection of a small fraction of the upstream ions converts the well known ion acoustic soliton into a structure with a steep potential gradient upstream and with downstream oscillations. The theory provides a simple interpretation of results dating back more than forty years but, more importantly, is shown to provide an explanation for recent observations on laser produced plasmas relevant to inertial fusion and to ion acceleration.

Cairns, R. A. [University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS (United Kingdom)] [University of St. Andrews, North Haugh, St. Andrews, Fife KY16 9SS (United Kingdom); Bingham, R.; Norreys, P.; Trines, R. [Central Laser Facility, STFC, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire OX11 0QX (United Kingdom)] [Central Laser Facility, STFC, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire OX11 0QX (United Kingdom)

2014-02-15

281

Natural laminar flow experiments on modern airplane surfaces  

NASA Technical Reports Server (NTRS)

Flight and wind-tunnel natural laminar flow experiments have been conducted on various lifting and nonlifting surfaces of several airplanes at unit Reynolds numbers between 0.63 x 10 to the 6th power/ft and 3.08 x 10 to the 6th power/ft, at Mach numbers from 0.1 to 0.7, and at lifting surface leading-edge sweep angles from 0 deg to 63 deg. The airplanes tested were selected to provide relatively stiff skin conditions, free from significant roughness and waviness, on smooth modern production-type airframes. The observed transition locations typically occurred downstream of the measured or calculated pressure peak locations for the test conditions involved. No discernible effects on transition due to surface waviness were observed on any of the surfaces tested. None of the measured heights of surface waviness exceeded the empirically predicted allowable surface waviness. Experimental results consistent with spanwise contamination criteria were observed. Large changes in flight-measured performance and stability and control resulted from loss of laminar flow by forced transition. Rain effects on the laminar boundary layer caused stick-fixed nose-down pitch-trim changes in two of the airplanes tested. No effect on transition was observed for flight through low-altitude liquid-phase clouds. These observations indicate the importance of fixed-transition tests as a standard flight testing procedure for modern smooth airframes.

Holmes, B. J.; Obara, C. J.; Yip, L. P.

1984-01-01

282

Laminar and Connectional Organization of a Multisensory Cortex  

PubMed Central

The transformation of sensory signals as they pass through cortical circuits has been revealed almost exclusively through studies of the primary sensory cortices, where principles of laminar organization, local connectivity and parallel processing have been elucidated. In contrast, almost nothing is known about the circuitry or laminar features of multisensory processing in higher-order, multisensory cortex. Therefore, using the ferret higher-order multisensory rostral posterior parietal (PPr) cortex, the present investigation employed a combination of multichannel recording and neuroanatomical techniques to elucidate the laminar basis of multisensory cortical processing. The proportion of multisensory neurons, the share of neurons showing multisensory integration, and the magnitude of multisensory integration were all found to differ by layer in a way that matched the functional or connectional characteristics of the PPr. Specifically, the supragranular layers (L2–3) demonstrated among the highest proportions of multisensory neurons and the highest incidence of multisensory response enhancement, while also receiving the highest levels of extrinsic inputs, exhibiting the highest dendritic spine densities, and providing a major source of local connectivity. In contrast, layer 6 showed the highest proportion of unisensory neurons while receiving the fewest external and local projections and exhibiting the lowest dendritic spine densities. Coupled with a lack of input from principal thalamic nuclei and a minimal layer 4, these observations indicate that this higher-level multisensory cortex shows unique functional and organizational modifications from the well-known patterns identified for primary sensory cortical regions. PMID:23172137

Foxworthy, W. Alex; Clemo, H. Ruth; Meredith, M. Alex

2012-01-01

283

The effects of gravity on wrinkled laminar flames  

SciTech Connect

Laminar and turbulent conical Bunsen type flames were used. The study compares results from normal gravity with the burner in an up-right orientation (+g), the burner inverted (-g), and in microgravity ([mu]g) by using the NASA Lewis drop tower facility. The primary diagnostic is a laser schlieren system and some LDA measurements were taken for the +g condition to measure the flow field. The +g laminar flame experiences a large amount of instabilities and results in an unsteady flame tip; cause is torroidal vortex rolling up between products and stagnate surrounding air. Comparison between LDA measurements in reactants and schlieren images shows that velocity fluctuation are induced at the same frequency as the roll up vortices are formed. This pumping of the reactant stream by the product/air interface instability in the +g case is also observed in the turbulent flames. In the -g arrangement the product/air interface is stable so there is no large pumping of the flame tip. At low flow rates the -g flames have flattened tips, but at higher flow rates they become conical in shape. When both flames. appear conical, the -g flames are longer for the same flow rate. In [mu]g the larger instabilities in the flame no longer exist as the product/air interface is believed to become stable. The laminar flames in [mu]g still show small instabilities over the entire flame.

Kostiuk, L.W.; Zhou, L.; Cheng, R.K.

1992-09-01

284

The effects of gravity on wrinkled laminar flames  

SciTech Connect

Laminar and turbulent conical Bunsen type flames were used. The study compares results from normal gravity with the burner in an up-right orientation (+g), the burner inverted (-g), and in microgravity ({mu}g) by using the NASA Lewis drop tower facility. The primary diagnostic is a laser schlieren system and some LDA measurements were taken for the +g condition to measure the flow field. The +g laminar flame experiences a large amount of instabilities and results in an unsteady flame tip; cause is torroidal vortex rolling up between products and stagnate surrounding air. Comparison between LDA measurements in reactants and schlieren images shows that velocity fluctuation are induced at the same frequency as the roll up vortices are formed. This pumping of the reactant stream by the product/air interface instability in the +g case is also observed in the turbulent flames. In the -g arrangement the product/air interface is stable so there is no large pumping of the flame tip. At low flow rates the -g flames have flattened tips, but at higher flow rates they become conical in shape. When both flames. appear conical, the -g flames are longer for the same flow rate. In {mu}g the larger instabilities in the flame no longer exist as the product/air interface is believed to become stable. The laminar flames in {mu}g still show small instabilities over the entire flame.

Kostiuk, L.W.; Zhou, L.; Cheng, R.K.

1992-09-01

285

Laminar-turbulent cycles in inclined lock-exchange flows.  

PubMed

We consider strongly confined, stably stratified shear flows generated as a lock exchange in a tube inclined at an angle of ?=45(?). This paper focuses on a transitional regime, in which the flow alternates between two distinct states: laminar, parallel shear flow and intense transverse motion characteristic of turbulence. Laminar-turbulent cycles were captured at Atwood numbers At?(?(2)-?(1))/(?(1)+?(2)) ranging from 2.45×10(-3) to 4.0×10(-3), where (?(1),?(2)) are the initial densities of the two fluids, with multiple cycles observed at At=2.55×10(-3). The evolution of the density and velocity fields in these flows was measured simultaneously using laser-induced fluorescence and particle image velocimetry. During each laminar-turbulent cycle, the axial velocity exhibits a distinctive ramp-cliff pattern, indicating that the flow accelerates as it relaminarizes, then decelerates rapidly as the Kelvin-Helmholtz billows break down. Within the range of experimental conditions, transverse stratification does not directly determine the onset of instability. Instead, the data suggest that a necessary criterion for the onset of instability is for the local Reynolds number to exceed 2200, with only a weak dependence on the Richardson number. PMID:23005207

Tanino, Yukie; Moisy, Frédéric; Hulin, Jean-Pierre

2012-06-01

286

Laminar and connectional organization of a multisensory cortex.  

PubMed

The transformation of sensory signals as they pass through cortical circuits has been revealed almost exclusively through studies of the primary sensory cortices, for which principles of laminar organization, local connectivity, and parallel processing have been elucidated. In contrast, almost nothing is known about the circuitry or laminar features of multisensory processing in higher order, multisensory cortex. Therefore, using the ferret higher order multisensory rostral posterior parietal (PPr) cortex, the present investigation employed a combination of multichannel recording and neuroanatomical techniques to elucidate the laminar basis of multisensory cortical processing. The proportion of multisensory neurons, the share of neurons showing multisensory integration, and the magnitude of multisensory integration were all found to differ by layer in a way that matched the functional or connectional characteristics of the PPr. Specifically, the supragranular layers (L2/3) demonstrated among the highest proportions of multisensory neurons and the highest incidence of multisensory response enhancement, while also receiving the highest levels of extrinsic inputs, exhibiting the highest dendritic spine densities, and providing a major source of local connectivity. In contrast, layer 6 showed the highest proportion of unisensory neurons while receiving the fewest external and local projections and exhibiting the lowest dendritic spine densities. Coupled with a lack of input from principal thalamic nuclei and a minimal layer 4, these observations indicate that this higher level multisensory cortex shows functional and organizational modifications from the well-known patterns identified for primary sensory cortical regions. PMID:23172137

Foxworthy, W Alex; Clemo, H Ruth; Meredith, M Alex

2013-06-01

287

The effect of debris accumulation on and filter resistance to airflow for four commercially available vacuum cleaners.  

PubMed

Mortar removal with right-angle grinders can cause excessive exposure to respirable crystalline silica. To control this dust exposure, vacuum cleaners need to exhaust 2.3 m(3)/min (80 cubic feet per minute) from the grinder's exhaust hood. Maintaining this airflow while collecting as much as 15.9 kg (35 lb) of debris in the vacuum cleaner has been problematic. A laboratory study was conducted to evaluate how mortar debris affects vacuum cleaner airflow and filter pressure loss. Four vacuum cleaners were tested. Two of the vacuum cleaners used vacuum cleaner bags as a prefilter; the other two vacuum cleaners used cyclones to reduce the amount of debris that reaches the filter. Test debris was collected by a masonry restoration contractor during actual mortar removal using a grinder fitted with a hood. The hood is attached to a vacuum cleaner with cyclonic pre-separation. The vacuum cleaner fan curves were obtained experimentally to learn how pressure loss affects vacuum cleaner airflows. Then, 15.9 kg (35 lb) of mortar removal debris was sucked into the vacuum cleaner in 2.27-kg (5-lb) increments. Before and after adding each 2.27-kg (5-lb) increment of debris, vacuum cleaner airflows were measured with a venturi meter, and vacuum cleaner static pressures were measured at the inlet to the vacuum cleaner motor, and before and after each filter. The vacuum cleaners equipped with cyclonic pre-separation were unaffected by the mass of debris collected in the vacuum cleaner and were able to maintain airflows in excess of 1.98 m(3)/min (70 cfm) throughout the testing program. As debris accumulated in the vacuum cleaners that used bags, airflow decreased from 2.3 m(3)/min (80 cfm) to as little as 0.85 m(3)/min (30 cfm). This airflow loss is caused by the increased airflow resistance of the bags that increased from less 0.03 kPa/m(3)/min (0.1 inches of water per cfm) to 16.7 kPa/m(3)/min (1.9 inches of water/cfm). Apparently, vacuum cleaners using bags should be used in applications where adequate dust control can be achieved at airflows less than 0.85 m(3)/min (30 cfm). Vacuum cleaners with cyclonic pre-separators provided superior and cost-effective dust control compared with vacuums with bags when dust loading was high and when more than 30 cfm of airflow is needed for dust control. PMID:19360515

Heitbrink, William A; Santalla-Elias, Javier

2009-06-01

288

Distributed educated throat stability bypass to increase the stable airflow range of a Mach 2.5 inlet with 60-percent internal contraction  

NASA Technical Reports Server (NTRS)

The results of an experimental investigation to increase the stable airflow operating range of a supersonic mixed-compression inlet are presented. A distributed educated throat stability-bypass entrance configuration was tested. In terms of diffuser-exit corrected airflow, a large inlet stable airflow range of about 16.1 percent was obtained if a constant pressure was maintained in the bypass plenum. Limited unstart angle of attack data are presented.

Shaw, R. J.; Mitchell, G. A.; Sanders, B. W.

1974-01-01

289

Effect of submucosal diathermy to the inferior turbinates on unilateral and total nasal airflow in patients with rhinitis.  

PubMed

The efficacy of the controversial treatment of submucosal diathermy to the inferior turbinates (SMDIT) was evaluated objectively. Twenty-seven patients with chronic rhinitis were investigated by hourly posterior rhinomanometry to assess changes in total and minimum (Fmin) and maximum (Fmax) unilateral nasal airflow over 5 h, before and 2-3 months after standardized SMDIT treatment. Nasal airflow was recorded at a sample pressure of 75 Pa and the results are reported as medians with interquartile range. Whilst SMDIT caused a significant 51% increase (p < 0.0001) in total nasal airflow from 246 cm3/s (131) to 371 cm3/s (133) the changes in unilateral airflow provided further evidence which strongly supported the benefits of this operation. Unilateral Fmin significantly increased by 136% (p < 0.0001) from 69 cm3/s (82) to 163 cm3/s (74) and Fmax significantly increased by 23% (p < 0.0001) from 171 cm3/s (74) to 211 cm3/s (59). The effect of surgery was to "splint" to the turbinate in a state of relative vasoconstriction. Our findings therefore provide functional evidence of submucosal fibrosis following SMDIT. The greater percentage change in unilateral Fmin suggests that this parameter is a more sensitive index of the effect of nasal surgery than total nasal airflow measurements. The importance of considering the nose as two separate airways in the evaluation of nasal treatments is emphasized. PMID:10728933

Quine, S M; Aitken, P M; Eccles, R

1999-01-01

290

Laminar circuit organization and response modulation in mouse visual cortex  

PubMed Central

The mouse has become an increasingly important animal model for visual system studies, but few studies have investigated local functional circuit organization of mouse visual cortex. Here we used our newly developed mapping technique combining laser scanning photostimulation (LSPS) with fast voltage-sensitive dye (VSD) imaging to examine the spatial organization and temporal dynamics of laminar circuit responses in living slice preparations of mouse primary visual cortex (V1). During experiments, LSPS using caged glutamate provided spatially restricted neuronal activation in a specific cortical layer, and evoked responses from the stimulated layer to its functionally connected regions were detected by VSD imaging. In this study, we first provided a detailed analysis of spatiotemporal activation patterns at specific V1 laminar locations and measured local circuit connectivity. Then we examined the role of cortical inhibition in the propagation of evoked cortical responses by comparing circuit activity patterns in control and in the presence of GABAa receptor antagonists. We found that GABAergic inhibition was critical in restricting layer-specific excitatory activity spread and maintaining topographical projections. In addition, we investigated how AMPA and NMDA receptors influenced cortical responses and found that blocking AMPA receptors abolished interlaminar functional projections, and the NMDA receptor activity was important in controlling visual cortical circuit excitability and modulating activity propagation. The NMDA receptor antagonist reduced neuronal population activity in time-dependent and laminar-specific manners. Finally, we used the quantitative information derived from the mapping experiments and presented computational modeling analysis of V1 circuit organization. Taken together, the present study has provided important new information about mouse V1 circuit organization and response modulation. PMID:23060751

Olivas, Nicholas D.; Quintanar-Zilinskas, Victor; Nenadic, Zoran; Xu, Xiangmin

2012-01-01

291

Instrumentation and measurement of airflow and temperature in attics fitted with ridge and soffit vents  

SciTech Connect

This study established a research facility where airflow velocities, temperature, and differential pressures could be measured at the ridge of an attic. Following the construction of a test building, sensors were constructed, calibrated, and installed inside the attic. Paired tests were performed for three different ridge vent treatments; two were rolled type vents and one was a baffled vent. When both attics were fitted with the same ridge vent, the airspeed and differential pressure profiles at the ridge were very similar for both attics, indicating that any observed differences in airspeed and differential pressure were caused by the ridge vent treatment used. The baffled vent and rolled vents were then installed on the ridge of the west and east attics, respectively. The data demonstrated that the baffled ridge vent provided a minimum of twice the ridge airspeed of the rolled vents, when all wind conditions were considered. On the day selected to study the direction of the airflows at the ridge, the baffled vent had airflow speeds at the ridge similar to the rolled vent without fabric backing. The baffled vent allowed air to come out of the attic through both sides of the ridge (negative differential pressures on both sides), while the rolled vent without fabric backing caused air to enter through the south side of the ridge and exit through the north side (positive differential pressure on the south side and negative differential pressure on the north), in effect short-circuiting the vent. The fabric-backed rolled vent allowed attic air to come out of the attic through both sides of the ridge, as did the baffled vent, but the airspeed was slower. The baffled vent was the one with the highest airspeed at the ridge and also had both sides of the vent under negative differential pressure, providing the most effective ventilation.

Romero, M.I.; Brenner, R.J. [USDA-ARS, Gainesville, FL (United States). Center for Medical Agricultural and Veterinary Entomology

1998-12-31

292

Numerical analysis of air-flow and temperature field in a passenger car compartment  

NASA Astrophysics Data System (ADS)

This paper presents a numerical study on the temperature field inside a passenger's compartment of a Proton Wira saloon car using computational fluid dynamics (CFD) method. The main goal is to investigate the effects of different glazing types applied onto the front and rear windscreens of the car on the distribution of air-temperature inside the passenger compartment in the steady-state conditions. The air-flow condition in the passenger's compartment is also investigated. Fluent CFD software was used to develop a three-dimensional symmetrical model of the passenger's compartment. Simplified representations of the driver and one rear passenger were incorporated into the CFD model of the passenger's compartment. Two types of glazing were considered namely clear insulated laminated tint (CIL) with a shading coefficient of 0.78 and green insulated laminate tint (GIL) with a shading coefficient of 0.5. Results of the CFD analysis were compared with those obtained when the windscreens are made up of clear glass having a shading coefficient of 0.86. Results of the CFD analysis show that for a given glazing material, the temperature of the air around the driver is slightly lower than the air around the rear passenger. Also, the use of GIL glazing material on both the front and rear windscreens significantly reduces the air temperature inside the passenger's compartment of the car. This contributes to a better thermal comfort condition to the occupants. Swirling air flow condition occurs in the passenger compartment. The air-flow intensity and velocity are higher along the side wall of the passenger's compartment compared to that along the middle section of the compartment. It was also found that the use of glazing materials on both the front and rear windscreen has no significant effects on the air-flow condition inside the passenger's compartment of the car.

Kamar, Haslinda Mohamed; Kamsah, Nazri; Mohammad Nor, Ahmad Miski

2012-06-01

293

8-Epi-PGF2alpha induces airflow obstruction and airway plasma exudation in vivo.  

PubMed

8-Epi-prostaglandin F2alpha (8-epi-PGF2alpha) is an F2-isoprostane formed mainly via noncyclooxygenase pathways in vivo. We investigated whether 8-epi-PGF2alpha has any effect on airflow obstruction and plasma exudation in vivo. Airflow obstruction was quantified by measuring lung resistance (RL) in anesthetized and ventilated guinea pigs, and plasma exudation was quantified by the Evans Blue dye method (20 mg/kg intravenously). Intratracheal instillation of 8-epi-PGF2alpha (1 nmol or 10 nmol) caused dose-related increases in RL. Furthermore, the higher dose of 8-epi-PGF2alpha produced Evans Blue dye extravasation in main bronchi and intrapulmonary airways. A prostanoid TP-receptor antagonist, BAY u3405 (1 mg/kg intravenously), abolished the airway effects of 8-epi-PGF2alpha (10 nmol). A thromboxane A2 (TxA2) synthase inhibitor, OKY-406 (30 mg/kg intravenously), significantly attenuated these effects of 8-epi-PGF2alpha (10 nmol). The level of TxB2, a stable TxA2 metabolite, increased in bronchoalveolar lavage fluid (BALF) after 8-epi-PGF2alpha instillation. We conclude that 8-epi-PGF2alpha causes airflow obstruction and plasma exudation in vivo. This effect may be mediated primarily via prostanoid TP-receptors, and a secondary generation of TxA2 may be involved in part of the airway responses in 8-epi-PGF2alpha in the guinea pig. PMID:9032175

Okazawa, A; Kawikova, I; Cui, Z H; Skoogh, B E; Lötvall, J

1997-02-01

294

Laminar flow transition: A large-eddy simulation approach  

NASA Technical Reports Server (NTRS)

A vectorized, semi-implicit code was developed for the solution of the time-dependent, three dimensional equations of motion in plane Poiseuille flow by the large-eddy simulation technique. The code is tested by comparing results with those obtained from the solutions of the Orr-Sommerfeld equation. Comparisons indicate that finite-differences employed along the cross-stream direction act as an implicit filter. This removes the necessity of explicit filtering along this direction (where a nonhomogeneous mesh is used) for the simulation of laminar flow transition into turbulence in which small scale turbulence will be accounted for by a subgrid scale turbulence model.

Biringen, S.

1982-01-01

295

Adaptive Solutions for Unsteady Laminar Flows on Unstructured Grids  

NASA Astrophysics Data System (ADS)

An adaptive finite volume method for the simulation of time-dependent, viscous flow is presented. The Navier-Stokes equations are discretized by central schemes on unstructured grids and solved by an explicit Runge-Kutta method. The essential topics of the present study are a new concept for a local Runge-Kutta time-stepping scheme, called multisequence Runge-Kutta, which reduces the severe stability restriction in unsteady problems, a common grid generation and adaptation procedure and the application of dynamic grids for capturing moving flow structures. Results are presented for laminar, separated flow around an aerofoil with a flap.

Vilsmeier, R.; Hänel, D.

1996-01-01

296

Two-dimensional laminar incompressible separated flow past airfoils  

NASA Technical Reports Server (NTRS)

A method is proposed to treat the problem of steady, two-dimensional, laminar, incompressible high Reynolds number separated flow past thin airfoils. An integral form of the boundary layer equations with interaction is used and the interaction between the inviscid and viscous flow fields is provided for by use of a thin-airfoil integral. Documentation of the attempts at obtaining a solution is presented. A survey of the current state-of-the-art of problems involving viscous-inviscid interactions in flow fields with separation is given.

Plotkin, A.

1973-01-01

297

Interaction of transient radiation in fully developed laminar flows  

NASA Technical Reports Server (NTRS)

The transient radiative interactions of nongray absorbing-emitting species in laminar fully-developed flows between two parallel plates are investigated analytically and numerically. The particular species considered are OH, CO, CO2, and H2O and different mixtures of these species. Transient and steady-state results are obtained for the temperature distribution and bulk temperature for different plate spacings, wall temperatures, and pressures. Results, in general, indicate that the rate of radiative heating can be quite high during earlier times. This information is useful in designing thermal protection systems for transient operations.

Tiwari, S. N.; Singh, D. J.

1987-01-01

298

Radiative interactions in laminar incompressible and compressible internal flows  

NASA Technical Reports Server (NTRS)

Analyses and numerical procedures are presented to investigate the radiative interactions of gray and nongray absorbing-emitting species between two parallel plates and in a circular tube. Laminar fully developed incompressible as well as entrance region subsonic flows are considered. The participating species considered are OH, CO, CO2, CH4, and H2O. Results obtained for different flow conditions indicate that the radiative interactions can be quite significant in fully developed incompressible flows. For subsonic flows, however, the flowfield is not changed significantly due to radiative interactions.

Tiwari, S. N.; Singh, D. J.; Trivedi, P. A.

1990-01-01

299

Analytical Study of Gravity Effects on Laminar Diffusion Flames  

NASA Technical Reports Server (NTRS)

A mathematical model is presented for the description of axisymmetric laminar-jet diffusion flames. The analysis includes the effects of inertia, viscosity, diffusion, gravity and combustion. These mechanisms are coupled in a boundary layer type formulation and solutions are obtained by an explicit finite difference technique. A dimensional analysis shows that the maximum flame width radius, velocity and thermodynamic state characterize the flame structure. Comparisons with experimental data showed excellent agreement for normal gravity flames and fair agreement for steady state low Reynolds number zero gravity flames. Kinetics effects and radiation are shown to be the primary mechanisms responsible for this discrepancy. Additional factors are discussed including elipticity and transient effects.

Edelman, R. B.; Fortune, O.; Weilerstein, G.

1972-01-01

300

Transient radiative energy transfer in incompressible laminar flows  

NASA Technical Reports Server (NTRS)

Analysis and numerical procedures are presented to investigate the transient radiative interactions of nongray absorbing-emitting species in laminar fully-developed flows between two parallel plates. The particular species considered are OH, CO, CO2, and H2O and different mixtures of these. Transient and steady-state results are obtained for the temperaure distribution and bulk temperature for different plate spacings, wall temperatures, and pressures. Results, in general, indicate that the rate of radiative heating can be quite high during earlier times. This information is useful in designing thermal protection systems for transient operations.

Tiwari, S. N.; Singh, D. J.

1987-01-01

301

Aircraft energy efficiency laminar flow control wing design study  

NASA Technical Reports Server (NTRS)

An engineering design study was performed in which laminar flow control (LFC) was integrated into the wing of a commercial passenger transport aircraft. A baseline aircraft configuration was selected and the wing geometry was defined. The LFC system, with suction slots, ducting, and suction pumps was integrated with the wing structure. The use of standard aluminum technology and advanced superplastic formed diffusion bonded titanium technology was evaluated. The results of the design study show that the LFC system can be integrated with the wing structure to provide a structurally and aerodynamically efficient wing for a commercial transport aircraft.

Bonner, T. F., Jr.; Pride, J. D., Jr.; Fernald, W. W.

1977-01-01

302

Unsteady Laminar CFD Simulation of Undulatory Rainbow Trout Swimming Hydrodynamics  

NASA Astrophysics Data System (ADS)

The propulsion mechanism of an undulatory swimming 10 cm rainbow trout (oncorhynchus mykiss) is studied using a laminar 2-D unsteady incompressible Navier-Stokes computational model with a moving adaptive mesh (Fluent 6.1). The wake mechanism is dominated by a reverse von Karman vortex street and compares well to previous experimental data. Thrust and drag forces are quantified and the equilibrium condition is satisfied within 5%. A method is developed to calculate hydrodynamic power using work, which results in a swimming efficiency of 62%. An investigation of the boundary layer shows incipient separation and highly unsteady velocity profiles.

Flanagan, Patrick; Hotchkiss, Rollin; Stock, David

2004-11-01

303

Polymer Effects on Heat Transport in Laminar Boundary Layer Flow  

E-print Network

We consider a laminar Blasius boundary-layer flow above a slightly heated horizontal plate and study the effect of polymer additives on the heat transport. We show that the action of the polymers can be understood as a space-dependent effective viscosity that first increases from the zero-shear value then decreases exponentially back to the zero-shear value as one moves away from the boundary. We find that with such an effective viscosity, both the horizontal and vertical velocities near the plate are decreased thus leading to an increase in the friction drag and a decrease in the heat transport in the flow.

Roberto Benzi; Emily S. C. Ching; Vivien W. S. Chu

2011-04-21

304

Hypothyroid cardiomyopathy complicated by a left ventricular laminar thrombus.  

PubMed

Clinical hypothyroidism is the most common hormone deficiency in the United States and is found in 0.3% of the U.S. population. It is associated with characteristic symptoms that can be readily identified by a careful history and physical examination. Hypothyroidism affects many bodily systems; in particular the cardiovascular system is impacted via multiple mechanisms.3 Occasionally hypothyroidism leads to transient left ventricular systolic dysfunction, termed hypothyroid cardiomyopathy. A rare sequela of this condition is a left ventricular thrombus, which has been described in two case reports thus far. Here we report a third case of reversible hypothyroid cardiomyopathy complicated by a left ventricular laminar thrombus. PMID:25438369

Van Treeck, Benjamin J; Masoud, Amgad G

2014-01-01

305

Theophylline in the management of airflow obstruction. 2. Difficult drugs to use, few clinical indications.  

PubMed Central

The narrow therapeutic index, potential toxicity, and need to monitor plasma concentrations make theophyllines difficult to use. Other drugs provide comparable or better bronchodilator and prophylactic efficacy. In asthma theophyllines should be considered for chronic stable asthma when treatment with optimal doses of inhaled steroids and bronchodilators fails to provide adequate control; for nocturnal asthma; and for prophylaxis and relief of symptoms in children and adults when inhaled treatment cannot be given. In general, theophyllines cannot be recommended for chronic airflow obstruction. A trial of theophylline is reasonable in individual patients whose symptoms remain troublesome despite a trial of steroids and optimal doses of inhaled bronchodilators. PMID:2186834

Johnston, I D

1990-01-01

306

Variable Speed Drive Volumetric Tracking (VSDVT) for Airflow Control in Variable Air Volume (VAV) Systems  

E-print Network

for both cases. The third and the fourth cases add the Static Pressure Reset (SPR) in the FT-1 and FT-2 cases. The SPR resets the static pressure proportionally to the square of the airflow. The correction constant is selected as zero in this study.... The fifth case adds the CO2 demand control (DC) in the FT-1 case. The sixth case adds both the SPR and DC into the FT-2 case. The seventh case uses both the volume tracking (VT) and the DC. The eighth case adds the SPR to the seventh case...

Liu, M.

2002-01-01

307

Airflow-field-induced sandwich-type membrane of block copolymer for selective ion separation.  

PubMed

A simple and effective airflow method to prepare sandwich-type block copolymer films is reported. The films are composed of three layers: vertically oriented nanocylinders align in both upper and bottom layers and irregular nanocylinders exist in the bulk of the film. The vertically oriented nanocylinders in both sides can provide high accessibility to ions and ensures the exchange of chemical species between the membrane and external environment, while the irregularly oriented nanocylinders in the middle part of the film can prolong the pathway of ions transportation and enhance ions selectivity. PMID:24497315

Shan, Feng; Lu, Xuemin; Guan, Junfang; Lu, Qinghua; Feng, Xingliang

2014-04-01

308

Measurement of effective pulmonary blood flow by soluble gas uptake in patients with chronic airflow obstruction.  

PubMed Central

A study was designed to assess the accuracy and reproducibility of rebreathing and single breath soluble gas uptake measurements of effective pulmonary blood flow (Q) in patients with airways obstruction. Both rebreathing (RB) and single breath (SB) estimates of Q were compared with direct Fick and thermodilution (TD) measurements of cardiac output at rest and during exercise in eight patients with chronic, poorly reversible airflow obstruction with mean FEV1 65% predicted and mean FEV1/FVC 53%. The mean (SD) resting values obtained were QRB 3.47 (0.46), QSB 4.75 (1.15), QFick 4.77 (0.97), and QTD 5.15 (0.98). QRB was significantly lower than the other three estimates, which did not differ significantly from each other. Exercise produced significant increases in all four estimates for the group. The mean exercise values were QRB 6.23 (1.19), QSB 7.62 (1.97), QFick 8.97 (1.96), and QTD 9.09 (1.00), both QRB and QSB being significantly less than QFick and QTD. Analysis of variance of the rest, exercise, and combined data showed highly significant relationships with the TD and Fick measurements for both QRB and QSB over the range of values studied. In addition, the reproducibility of QRB and QSB was assessed in 15 other patients with chronic airflow obstruction (mean FEV1 42% predicted, FEV1/FVC 43%) and in 10 normal subjects. The coefficients of intrasubject variability for a single measurement for QRB were 8.7% in normal subjects and 10.2% in patients and for QSB were 11.7% in normal subjects and 16.1% in patients. The group differences from morning to afternoon, between days, and over a month were not significant in the normal subjects. In the patients QRB was slightly higher in the afternoon than in the morning of the same day, but the differences between days and over a month were not significant for either test. Although both tests detected the increase in pulmonary blood flow during exercise, the single breath test was more accurate at rest. Some underestimation was present for rebreathing at rest and for both tests during exercise, but this can be allowed for. In patients with mild airflow obstruction the reproducibility of the soluble gas uptake methods was similar to that of invasive catheter methods of cardiac output estimation. The single breath test in particular was, however, less reproducible in patients with more severe airflow obstruction, and the rebreathing method may be more useful for detecting increases in pulmonary blood flow in these patients. PMID:3660313

Pierce, R J; McDonald, C F; Thuys, C A; Rochford, P D; Barter, C E

1987-01-01

309

Airflow Characteristics of Direct-Type Kitchen Hood Systems in High-Rise Apartment Buildings  

E-print Network

if the adoption of direct- type systems alone in place of the shared-type would yield the level of capture efficiency close to the hood design specification. 3 4 5 6 Figure 1: Layout of apartment used to analyze airflow 7 (a)?24?hour?temperature?distribution?for?Jan....?1st (from?CONTAM?input) (b)?24?hour?wind?speed?distribution?for?Jan.?1st (CONTAM?input) Figure 2: Example of CONTAM input for the 1st of January 8 (c)?24?hour?wind?direction?distribution?for?Jan.?1st (CONTAM?input) Figure 2: Example of CONTAM...

Park, M.

2011-01-01

310

Terminal Box Airflow Reset: An Effective Operation and Control Strategy for Comfort Improvement and Energy Conservation  

E-print Network

Conservation M. Liu Ph.D. P. E. M. Abbas P. E. Y. Zhu Ph.D., P. E. D. E. Claridge Ph.D., P. E. Energy Systems Laboratory Sempra Energy Solutions SSR Inc Energy Systems Laboratory University of Nebraska-Lincoln Houston Houston Texas A&M University... for constant air volume terminal boxes during unoccupied hours. Authors have implemented the airflow reset in dual duct variable air volume terminal boxes [Abbas and Liu, 1996], in dual duct constant air volume terminal boxes [Liu and Zhu, 1998...

Liu, M.; Abbas, M.; Zhu, Y.; Claridge, D. E.

2002-01-01

311

Laminar flow control leading edge glove flight test article development  

NASA Technical Reports Server (NTRS)

A laminar flow control (LFC) flight test article was designed and fabricated to fit into the right leading edge of a JetStar aircraft. The article was designed to attach to the front spar and fill in approx. 70 inches of the leading edge that are normally occupied by the large slipper fuel tank. The outer contour of the test article was constrained to align with an external fairing aft of the front spar which provided a surface pressure distribution over the test region representative of an LFC airfoil. LFC is achieved by applying suction through a finely perforated surface, which removes a small fraction of the boundary layer. The LFC test article has a retractable high lift shield to protect the laminar surface from contamination by airborne debris during takeoff and low altitude operation. The shield is designed to intercept insects and other particles that could otherwise impact the leading edge. Because the shield will intercept freezing rain and ice, a oozing glycol ice protection system is installed on the shield leading edge. In addition to the shield, a liquid freezing point depressant can be sprayed on the back of the shield.

Pearce, W. E.; Mcnay, D. E.; Thelander, J. A.

1984-01-01

312

Laminar-flow fluid mixer for fast fluorescence kinetics studies.  

PubMed

The ability to mix aqueous liquids on microsecond time scales, while consuming minimal amounts of sample and maintaining UV-visible optical access to the mixing region, is highly desirable for a range of biophysical studies of fast protein and nucleic acid interactions and folding. We have constructed a laminar coaxial jet mixer that allows the measurement of UV-excited fluorescence from nanoliter and microliter quantities of material, mixed at microsecond rates. The mixer injects a narrow cylindrical stream (radius a < 1 microm) of fluorescent sample into a larger flow of diluting buffer that moves through a capillary (100 microm i.d.) at a speed approximately 20 cm/s, under laminar flow conditions (Re approximately equal to 14). Construction from a fused silica capillary allows the laser excitation (at 266 nm) and detection (at 350 nm) of tryptophan fluorescence at reasonably low working concentrations, without interference from background fluorescence. Using this mixer we have measured sub-millisecond fluorescence quenching kinetics while consuming fluorescent sample at rates no greater than 6 nl/s. Consumption of the diluting buffer is also very modest (approximately 1-3 microl/s) in comparison with other rapid mixer designs. PMID:12414719

Pabit, Suzette A; Hagen, Stephen J

2002-11-01

313

Experimental investigation of flow instabilities in a laminar separation bubble  

NASA Astrophysics Data System (ADS)

The present paper reports the results of a detailed experimental study aimed at investigating the dynamics of a laminar separation bubble, from the origin of separation up to the breakdown to turbulence of the large scale coherent structures generated as a consequence of the Kelvin-Helmholtz instability process. Measurements have been performed along a flat plate installed within a double contoured test section, designed to produce an adverse pressure gradient typical of Ultra-High-Lift turbine blade profiles, which induces the formation of a laminar separation bubble at low Reynolds number condition. Measurements have been carried out by means of complementary techniques: hot-wire (HW) anemometry, Laser Doppler Velocimetry (LDV) and Particle Image Velocimetry (PIV). The high accuracy 2-dimensional LDV results allow investigating reverse flow magnitude and both Reynolds normal and shear stress distributions along the separated flow region, while the high frequency response of the HW anemometer allows analyzing the amplification process of flow oscillations induced by instability mechanisms. PIV results complement the flow field analysis providing information on the generation and evolution of the large scale coherent structures shed as a consequence of the separated shear layer roll-up, through instantaneous velocity vector maps. The simultaneous analysis of the data obtained by means of the different measuring techniques allows an in depth view of the instability mechanisms involved in the transition/reattachment processes of the separated shear layer.

Simoni, D.; Ubaldi, M.; Zunino, P.

2014-06-01

314

Heat Transfer Effects on Laminar Velocity Profiles in Pipe Flow  

NASA Astrophysics Data System (ADS)

Heat Transfer Effects on Laminar Velocity Profiles in Pipe Flow. Robert L. Powell, Thomas P. Jenkins Department of Chemical Engineering & Materials Science University of California, Davis, CA 95616 Using laser Doppler velocimetry, we have measured the axial velocity profiles for steady, pressure driven, laminar flow of water in a circular tube. The flow was established in a one inch diameter seamless glass tube. The entry length prior to the measuring section was over one hundred diameters. Reynolds numbers in the range 500-2000 were used. Under conditions where the temperature difference between the fluid and the surroundings differed by as little as 0.2C, we found significant asymmetries in the velocity profiles. This asymmetry was most pronounced in the vertical plane. Varying the temperature difference moved the velocity maximum either above or below the centerline depending upon whether the fluid was warmer or cooler than the room. These results compare well to existing calculations. Using the available theory and our experiments it is possible to identify parameter ranges where non-ideal conditions(not parabolic velocity profiles) will be found. Supported by the EMSP Program of DOE.

Powell, Robert; Jenkins, Thomas

1998-11-01

315

Streamwise Vorticity Generation in Laminar and Turbulent Jets  

NASA Technical Reports Server (NTRS)

Complex streamwise vorticity fields are observed in the evolution of non-circular jets. Generation mechanisms are investigated via Reynolds-averaged (RANS), large-eddy (LES) and direct numerical (DNS) simulations of laminar and turbulent rectangular jets. Complex vortex interactions are found in DNS of laminar jets, but axis-switching is observed only when a single instability mode is present in the incoming mixing layer. With several modes present, the structures are not coherent and no axis-switching occurs, RANS computations also produce no axis-switching. On the other hand, LES of high Reynolds number turbulent jets produce axis-switching even for cases with several instability modes in the mixing layer. Analysis of the source terms of the mean streamwise vorticity equation through post-processing of the instantaneous results shows that, complex interactions of gradients of the normal and shear Reynolds stresses are responsible for the generation of streamwise vorticity which leads to axis-switching. RANS computations confirm these results. k - epsilon turbulence model computations fail to reproduce the phenomenon, whereas algebraic Reynolds stress model (ASM) computations, in which the secondary normal and shear stresses are computed explicitly, succeeded in reproducing the phenomenon accurately.

Demuren, Aodeji O.; Wilson, Robert V.

1999-01-01

316

Laminar cortical necrosis in adrenal crisis: sequential changes on MRI.  

PubMed

We describe the serial magnetic resonance imaging (MRI) findings in a six-year-old girl with congenital adrenal hyperplasia, who presented with seizures and unconsciousness during a hypoadrenal crisis. Initial neuroimaging revealed the presence of brain edema with high signal changes in the fronto-parietal cortex on diffusion-weighted MRI. The brain edema worsened four days into admission, and by day 14 low-density areas were seen over the frontal lobes bilaterally using computed tomography (CT). Follow-up MRI at between one and two months of admission revealed extensive white matter lesions with high intensity on T2-weighted images (T2WI) and fluid-attenuated inversion recovery (FLAIR) images, which extended into deep cortical layers. Additionally, linear lesions with high signal change on T1-weighted imaging developed in the superficial cortical layers, with frontal predominance. This layer appeared isointense on T2WI and high intensity on FLAIR images, suggesting laminar cortical necrosis. Two months later, linear, cavitary lesions appeared in the middle cortical layers between the aforementioned superficial laminar abnormality and deep cortex/white matter lesions. The high-intensity signals in the deep cortical layers remained contiguous with the white matter lesions. This unique type of multi-layered cortical lesion may have resulted from a complex combination of hypoglycemia and hypoxia/ischemia in the setting of adrenal insufficiency. PMID:17590301

Saito, Yoshiaki; Ogawa, Toshihide; Nagaishi, Jun-ichi; Inoue, Takehiko; Maegaki, Yoshihiro; Ohno, Kousaku

2008-01-01

317

Low temperature high current ion beams and laminar flows  

NASA Astrophysics Data System (ADS)

Self-consistent Vlasov-Poisson equilibria for the extraction of ions with low temperature Ti are discussed, with comparison to the laminar flow case Ti = 0, in two dimensional diodes. Curvilinear coordinates aligned with laminar beam flow lines are extended to the low ion temperature case, with a reduced current density jd, expressed with cathode integrals. This generalizes one-dimensional interpolation between rays along the cathode coordinate to multidimensional integrations, including also the momentum components, so that jd is free from the granularity defect and noise, typical of standard ray tracing approach. A robust numerical solution procedure is developed, which allows studying current saturated extraction and drift tube effects. A discussion of particle initial conditions determines the emission angles and shows that temperature effect at beam edge is partly balanced by the focus electrode inclination. Results for a typical diode are described, with detail about normalized emittance, here taken strictly proportional to the x - px phase space area, for a beam with non uniform velocities. Contribution to the Topical Issue "Theory and Applications of the Vlasov Equation", edited by Francesco Pegoraro, Francesco Califano, Giovanni Manfredi and Philip J. Morrison.

Cavenago, Marco

2014-07-01

318

A numerical study of laminar heat convection in ducts of irregular cross-sections  

Microsoft Academic Search

Prediction of laminar flow convective heat transfer rates in ducts of both arbitrary and irregularly shaped boundaries is important for the proper design of compact heat exchangers and other heat transfer equipment. Forced convective heat transfer during hydrodynamically fully developed laminar fluid flow inside ducts of irregular cross section is analyzed utilizing numerical methods. The elliptic grid generation technique is

I. Uzun; M. Uensal

1997-01-01

319

Exploring Roughness Effect on Laminar Internal Flow–Are We Ready for Change?  

Microsoft Academic Search

Laminar flow is often encountered in the channels of microdevices as a result of the small hydraulic diameters. The roughness introduced on the walls of these channels through various fabrication techniques, such as etching, micromachining, laser drilling, etc., results in a high value of relative roughness (defined as the wall surface roughness to channel hydraulic diameter ratio). Laminar flow in

Satish G. Kandlikar

2008-01-01

320

Discussion of test results in the design of laminar airfoils for competition gliders  

NASA Technical Reports Server (NTRS)

The deformation of flow in the boundary layer and the local separation of a laminar layer (laminar bubbles) from various airfoils were investigated. These phenomena were classified and their influence is discussed. Various aerodynamic characteristics are discussed and the principles for prescribing pressure distribution to attain a high value of c sub z max with a possibly low drag coefficient are described.

Ostrowski, J.; Skrzynski, S.; Litwinczyk, M.

1980-01-01

321

A Power-Law Formulation of Laminar Flow in Short Pipes Max Sherman  

E-print Network

A Power-Law Formulation of Laminar Flow in Short Pipes Max Sherman Indoor Environment Program-law representation between the air flow and applied pressure for laminar flow in short pipes. It is found that short of interest. The system studied herein is the flow of an incompressible, viscous fluid through a short pipe

322

Equine neutrophil elastase in plasma, laminar tissue, and skin of horses administered black walnut heartwood extract  

Microsoft Academic Search

Laminitis is a local manifestation of a systemic inflammatory response that is characterized by neutrophil activation and movement of neutrophils into the laminar tissues. Given the evidence for the involvement of neutrophils in the development of laminitis, we measured concentrations of neutrophil elastase, a serine protease released from the azurophilic granules of neutrophils, in plasma, skin and laminar tissues obtained

Geoffroy de la Rebière de Pouyade; Laura M. Riggs; James N. Moore; Thierry Franck; Ginette Deby-Dupont; David J. Hurley; Didier Serteyn

2010-01-01

323

Field characterization of three-dimensional lee-side airflow patterns under offshore winds at a beach-dune system  

NASA Astrophysics Data System (ADS)

Characterization of three-dimensional (3D) airflow remains elusive within a variety of environments and is particularly challenging over complex dune topography. Previous work examining airflow over and in the lee of dunes has been restricted to two-dimensional studies and has concentrated on dune shapes containing angle of repose lee sides only. However, the presence of vegetation in coastal dunes creates topographic differences and irregular shapes that interfere with flow separation at the crest and significantly modify lee-side airflow patterns and potential transport. This paper presents the first 3D field characterization of airflow patterns at the lee side of a subaerial dune. Flow information was obtained using an array of 3D ultrasonic anemometers deployed over a beach surface during seven offshore wind events. Data were used to measure cross-shore and alongshore lee-side airflow patterns using the three dimensions of the wind vector. Distances to re-attachment were similar to previous studies, but the range of transverse incident wind directions resulting in flow separation (0+/-35°) was almost twice that previously reported (0+/-20°). Airflow reversal took place with winds as slow as 1 m s-1. Transverse offshore winds generated areas of opposing wind directions both within the reversed zone and beyond re-attachment, contrary to consistent deflection in only one direction found in transverse desert dunes. Patterns of flow convergence-divergence have been reported in fluvial studies. However, while convergence was associated with weak reversal in fluvial settings, it appeared to be related to strong flow reversal here and could be produced by pressure differentials at the dune crest.

Delgado-Fernandez, Irene; Jackson, Derek W. T.; Cooper, J. Andrew G.; Baas, Andreas C. W.; Beyers, J. H. Meiring; Lynch, Kevin

2013-06-01

324

Scanning LDV for vibration measurement of filiform hairs in crickets in response to induced airflow  

NASA Astrophysics Data System (ADS)

Cercal hairs represent in cricket a wind sensitive escape system, able to detect the airflow generated from predating species. These sensors have been studied as a biomimetic concept to allow the development of MEMS for biomedical use. In particular, the behaviour of the hairs, including airflow response, resonant frequency and damping, has been investigated up to a frequency of 20 kHz. The microscopic nature of the hairs, the complex vibrations of excited hairs and the high damping of the system suggested that the use of Laser Doppler vibrometry could possibly improve the test performance. Two types of tests were performed: in the first case the hairs were indirectly excited using the signal obtained from a vibrating aluminium plate, whilst in the second case the hairs were directly excited using a white noise chirp. The results from the first experiment indicated that the hairs move in-phase with the exciting signal up to frequencies in the order of 10 kHz, responding to the vibration modes of the plate with a signal attenuation of 12 to 20 dB. The chirp experiment revealed the presence of rotational resonant modes at 6850 and 11300 Hz. No clear effect of hair length was perceivable on the vibration response of the filiform sensors. The obtained results proved promising to support the mechanical and vibration characterisation of the hairs and suggest that scanning Laser vibrometry can be used extensively on highly dampened biological materials.

Santulli, C.; Finn, T. J.; Seidel, R.; Jeronimidis, G.

2006-06-01

325

A Numerical Model of Viscoelastic Layer Entrainment by Airflow in Cough  

NASA Astrophysics Data System (ADS)

Coughing is an alternative mode of ensuring mucus clearance in the lung when normal cilia induced flow breaks down. A numerical model of this process is presented with the following aspects. (1) A portion of the airway comprising the first three bronchus generations is modeled as radially reinforced elastic tubes. Elasticity equations are solved to predict airway deformation under effect of airway pressure. (2) The compressible, turbulent flow induced by rapid lung contraction is modeled by direct numerical simulation for Reynolds numbers in the range 5,000-10,000 and by Large Eddy Simulation for Reynolds numbers in the range 5,000-40,000. (3) A two-layer model of the airway surface liquid (ASL) covering the airway epithelial layer is used. The periciliary liquid (PCL) in direct contact with the epithelial layer is considered to be a Newtonian fluid. Forces modeling cilia beating can act upon this layer. The mucus layer between the PCL and the interior airflow is modeled as an Oldroyd-B fluid. The overall computation is a fluid-structure interaction simulation that tracks changes in ASL thickness and airway diameters that result from impulsive airflow boundary conditions imposed at bronchi ends. In particular, the amount of mucus that is evacuated from the system is computed as a function of cough intensity and mucus rheological properties.

Mitran, Sorin M.

2008-07-01

326

Flight Test Results from the Rake Airflow Gage Experiment on the F-15B Airplane  

NASA Technical Reports Server (NTRS)

The Rake Airflow Gage Experiment involves a flow-field survey rake that was flown on the Propulsion Flight Test Fixture at the NASA Dryden Flight Research Center using the Dryden F-15B research test bed airplane. The objective of this flight test was to ascertain the flow-field angularity, local Mach number profile, total pressure distortion, and dynamic pressure at the aerodynamic interface plane of the Channeled Centerbody Inlet Experiment. This new mixed-compression, supersonic inlet is planned for flight test in the near term. Knowledge of the flow-field characteristics at this location underneath the airplane is essential to flight test planning and computational modeling of the new inlet, an< it is also applicable for future propulsion systems research that may use the Propulsion Flight Test Fixture. This report describes the flight test preparation and execution, and the local flow-field properties calculated from pressure measurements of the rake. Data from the two Rake Airflow Gage Experiment research flights demonstrate that the F-15B airplane, flying at a free-stream Mach number of 1.65 and a pressure altitude of 40,000 ft, would achieve the desired local Mach number for the future inlet flight test. Interface plane distortion levels of 2 percent and a local angle of attack of -2 deg were observed at this condition. Alternative flight conditions for future testing and an exploration of certain anomalous data also are provided.

Frederick, Michael A.; Ratnayake, Nalin A.

2011-01-01

327

Flight Test Results from the Rake Airflow Gage Experiment on the F-15B Airplane  

NASA Technical Reports Server (NTRS)

The Rake Airflow Gage Experiment involves a flow-field survey rake that was flown on the Propulsion Flight Test Fixture at the NASA Dryden Flight Research Center using the Dryden F-15B research test bed airplane. The objective of this flight test was to ascertain the flow-field angularity, local Mach number profile, total pressure distortion, and dynamic pressure at the aerodynamic interface plane of the Channeled Centerbody Inlet Experiment. This new mixed-compression, supersonic inlet is planned for flight test in the near term. Knowledge of the flow-field characteristics at this location underneath the airplane is essential to flight test planning and computational modeling of the new inlet, and it is also applicable for future propulsion systems research that may use the Propulsion Flight Test Fixture. This report describes the flight test preparation and execution, and the local flowfield properties calculated from pressure measurements of the rake. Data from the two Rake Airflow Gage Experiment research flights demonstrate that the F-15B airplane, flying at a free-stream Mach number of 1.65 and a pressure altitude of 40,000 ft, would achieve the desired local Mach number for the future inlet flight test. Interface plane distortion levels of 2 percent and a local angle of attack of 2 were observed at this condition. Alternative flight conditions for future testing and an exploration of certain anomalous data also are provided.

Frederick, Michael A.; Ratnayake, Nalin A.

2010-01-01

328

Detailed predictions of particle aspiration affected by respiratory inhalation and airflow  

NASA Astrophysics Data System (ADS)

The effects of air pollution found in the atmosphere and exposure to airborne particles are an important problem in the interest of public health. Exposure to contaminated air under different flow conditions is studied using the latest computational fluid dynamics models. For the first time the upper respiratory airway is integrated into a human body and placed inside a room, facing different airflow speeds (0.05-0.35 m s-1). It was found that the airflow streamlines diverged as it approached the human body, at the torso and accelerated upwards past the face and head before separating at the rear of the head, forming recirculating regions in the wake behind the body. Inhaled particles were tracked backwards to determine its origins. At a plane upstream from the face the locations of particles inhaled form a region known as the critical area, which is presented. This study establishes a better understanding of particle inhalability and provides a step towards a more holistic approach in determining inhalation toxicology effects of exposure to atmospheric particles.

Inthavong, Kiao; Ge, Qin Jiang; Li, Xiang Dong; Tu, Ji Yuan

2012-12-01

329

Effects of surface roughness on evaporation from porous surfaces into turbulent airflows  

NASA Astrophysics Data System (ADS)

The ubiquitous and energy intensive mass transfer between wet porous surfaces and turbulent airflows is of great importance for various natural and industrial applications. The roughness of natural surfaces is likely to influence the structure of adjacent boundary layer and thus affecting heat and mass fluxes from surfaces. These links were formalized in a new model that considers the intermittent turbulence-induced boundary layer with local mass and energy exchange rates. We conducted experiments with regular surface roughness patterns subjected to constant turbulent airflows and monitored mass loss and thermal signatures of localized evaporative fluxes using infrared thermography. The resulting patterns were in good agreement with model predictions for local and surface averaged turbulent exchange rates. Preliminary results obtained for evaporation from sinusoidal wavy soil surfaces reveal that evaporative fluxes can be either enhanced or suppressed (relative to a flat surface) owing to relative contribution of downstream (separation zone) and rising (reattachment zone) surfaces of the wave with thick and thin viscous sublayer thicknesses, respectively. For isolated roughness elements (bluff bodies) over a flat evaporating surface, the resulting fluxes are enhanced (relative to a smooth surface) due to formation of vortices that induce thinner boundary layer. Potential benefits of the study for interpretation and upscaling of evaporative and heat fluxes from natural (rough) terrestrial surfaces will be discussed. Keywords: Turbulent Evaporation, Porous Media, Surface Roughness, Infrared Thermography.

Haghighi, Erfan; Or, Dani

2014-05-01

330

Airflow obstruction and left ventricular filling pressure in suspected chronic obstructive pulmonary disease.  

PubMed

Left ventricular (LV) filling impairment is present in patients with chronic obstructive pulmonary disease (COPD). Airflow obstruction is related to reduced LV end-diastolic volume, stroke volume, and cardiac output. The ratio of peak early diastolic filling velocity of the mitral inflow to peak early diastolic velocity of the mitral annulus (E/e'), an echocardiographic parameter, can be applied as a surrogate marker of LV filling pressures. Forty-seven individuals with suspected COPD underwent pulmonary function tests and echocardiography. The ratio of forced expiratory volume in 1s to forced vital capacity (FEV1/FVC) and the E/e' ratio were determined. Multivariate linear regression analysis showed that the FEV1/FVC ratio (?=0.01; 95% confidence interval, 0.001-0.019; p=0.036) independently predicted the log transformed E/e' ratio. An increase of FEV1/FVC ratio (in percentage) by 1 unit was associated with an increase of the E/e' ratio multiplied by 1.01. Airflow obstruction inversely predicts LV filling pressure in suspected COPD cases. PMID:24361463

Yu, Yung-Huey; Chen, Ming-Zen; Wen, Li-Li; Chu, Ching-Chi; Chiang, Chih-Teng; Chen, Chung-Hua; Lin, Yueh-Juh

2014-02-01

331

Calibration for Thrust and Airflow Measurements in the CE-22 Advanced Nozzle Test Facility  

NASA Technical Reports Server (NTRS)

CE-22 facility procedures and measurements for thrust and airflow calibration obtained with choked-flow ASME nozzles are presented. Six calibration nozzles are used at an inlet total pressure from 20 to 48 psia. Throat areas are from 9.9986 to 39.986 sq. in.. Throat Reynolds number varies from 1.8 to 7.9 million. Nozzle gross thrust coefficient (CFG) uncertainty is 0.25 to 0.75 percent, with smaller uncertainly generally for larger nozzles and higher inlet total pressure. Nozzle discharge coefficient (CDN) uncertainty is 0.15 percent or less for all the data. ASME nozzle calibrations need to be done before and after research model testing to achieve these uncertainties. In addition, facility capability in terms of nozzle pressure ratio (NPR) and nozzle airflow are determined. Nozzle pressure ratio of 50 or more is obtainable at 40 psia for throat areas between 20 and 30 sq. in.. Also presented are results for two of the ASME nozzles vectored at 10deg, a dead-weight check of the vertical (perpendicular to the jet axis) force measurement, a calibration of load cell forces for the effects of facility tank deflection with tank pressure, and the calibration of the metric-break labyrinth seal.

Werner, Roger A.; Wolter, John D.

2010-01-01

332

Evaluation of an experimental short-length annular combustor: One-side-entry dilution airflow concept  

NASA Technical Reports Server (NTRS)

A test program was conducted to evaluate an experimental short-length annular combustor that uses a one-side-entry dilution airflow concept. The combustor design features scoops on the outer liner for controlling the primary- and secondary-zone airflow distribution. Combustor inlet total pressures were limited to 62 N/sq cm (90 psia) with inlet-air temperatures from 590 K (600 F) to 890 K (1150 F). At a diffuser inlet Mach number of 0.25, the exit temperature pattern factor was 0.44 with an average exit temperature of 1436 K (2124 F) and a total pressure loss of 4.3 percent. At a diffuser inlet Mach number of 0.31, the exit temperature pattern factor was reduced to 0.29 with an average exit temperature of 1450 K (2151 F) and a total pressure loss of 6.1 percent. Nominal combustion efficiencies of 100 percent were obtained with the ASTM A-1 fuel. Exhaust gas emissions, smoke, and altitude relight data are included with exit-temperature profiles and distribution patterns.

Humenik, F. M.; Biaglow, J. A.

1973-01-01

333

An experimental study of a plasma actuator in absence of free airflow: Ionic wind velocity profile  

SciTech Connect

In this study, we are interested in the direct current electrical corona discharge created between two wire electrodes. The experimental results are related to some electroaerodynamic actuators based on the direct current corona discharge at the surface of a dielectric material. Several geometrical forms are selected for the dielectric surface, such as a plate, a cylinder, and a NACA 0015 aircraft wing. The current density-electric field characteristics are presented for different cases in order to determine the discharge regimes. The corona discharge produces nonthermal plasma, so it is called plasma discharge. Plasma discharge creates a tangential ionic wind above the surface at the vicinity of the wall. The ionic wind induced by the corona discharge is measured in absence of free external airflow. The ionic wind velocity profiles and the maximum induced tangential force are given for different surface forms, so it is possible to compare the actuators effect based on the span of the ionic wind velocity and thrust values. The higher ionic wind velocity is obtained with the NACA profile, which shows the effectiveness of this actuator for the airflow control.

Mestiri, R.; Hadaji, R.; Ben Nasrallah, S. [Ecole Nationale d'Ingenieurs de Monastir, Monastir 5019 (Tunisia)

2010-08-15

334

Airflow reduction during cold weather operation of residential heat recovery ventilators  

SciTech Connect

Laboratory measurements of the performance of residential heat recovery ventilators have been carried out for the R-2000 Energy Efficient Home Program. This work was based on a preliminary test procedure developed by the Canadian Standards Association, part of which calls for testing the HRV under cold weather conditions. An environmental chamber was used to simulate outdoor conditions. Initial tests were carried out with an outdoor temperature of -20/sup 0/C; subsequent tests were carried out at a temperature of -25/sup 0/C. During the tests, airflows, temperatures, and relative humidities of airstreams entering and leaving the HRV, along with electric power inputs, were monitored. Frost buildup in the heat exchangers and defrost mechanisms, such as fan shutoff or recirculation, led to reductions in airflows. The magnitude of the reductions is dependent on the design of the heat exchanger and the defrost mechanism used. This paper presents the results of tests performed on a number of HRVs commercially available in Canada at the time of the testing. The flow reductions for the various defrost mechanisms are discussed.

McGugan, C.A.; Edwards, P.F.; Riley, M.A.

1987-06-01

335

Simultaneous imaging of two-dimensional electron density and air-flow distribution over air-blast decaying arc  

NASA Astrophysics Data System (ADS)

Sensitive Shack-Hartmann type laser wavefront sensors were applied to simultaneous imaging of two-dimensional electron density and air-flow distributions over decaying arc channels under air blasting with several pressures. Our experimental results showed that higher blasting pressures facilitated the rapid reduction of arc diameters and an increase in the electron densities around the gap centre due not only to the thermal pinch effect but also to air-flow disturbances, although there were no significant effects of the air blasting on the arc conductance.

Inada, Yuki; Yamagami, Shimpei; Matsuoka, Shigeyasu; Kumada, Akiko; Ikeda, Hisatoshi; Hidaka, Kunihiko

2014-08-01

336

Monitoring minimization of grade B environments based on risk assessment using three-dimensional airflow measurements and computer simulation.  

PubMed

A practical, risk-based monitoring approach using the combined data collected from actual experiments and computer simulations was developed for the qualification of an EU GMP Annex 1 Grade B, ISO Class 7 area. This approach can locate and minimize the representative number of sampling points used for microbial contamination risk assessment. We conducted a case study on an aseptic clean room, newly constructed and specifically designed for the use of a restricted access barrier system (RABS). Hotspots were located using three-dimensional airflow analysis based on a previously published empirical measurement method, the three-dimensional airflow analysis. Local mean age of air (LMAA) values were calculated based on computer simulations. Comparable results were found using actual measurements and simulations, demonstrating the potential usefulness of such tools in estimating contamination risks based on the airflow characteristics of a clean room. Intensive microbial monitoring and particle monitoring at the Grade B environmental qualification stage, as well as three-dimensional airflow analysis, were also conducted to reveal contamination hotspots. We found representative hotspots were located at perforated panels covering the air exhausts where the major piston airflows collect in the Grade B room, as well as at any locations within the room that were identified as having stagnant air. However, we also found that the floor surface air around the exit airway of the RABS EU GMP Annex 1 Grade A, ISO Class 5 area was always remarkably clean, possibly due to the immediate sweep of the piston airflow, which prevents dispersed human microbes from falling in a Stokes-type manner on settling plates placed on the floor around the Grade A exit airway. In addition, this airflow is expected to be clean with a significantly low LMAA. Based on these observed results, we propose a simplified daily monitoring program to monitor microbial contamination in Grade B environments. To locate hotspots we propose using a combination of computer simulation, actual airflow measurements, and intensive environmental monitoring at the qualification stage. Thereafter, instead of particle or microbial air monitoring, we recommend the use of microbial surface monitoring at the main air exhaust. These measures would be sufficient to assure the efficiency of the monitoring program, as well as to minimize the number of surface sampling points used in environments surrounding a RABS. PMID:19174953

Katayama, Hirohito; Higo, Takashi; Tokunaga, Yuji; Katoh, Shigeo; Hiyama, Yukio; Morikawa, Kaoru

2008-01-01

337

Feasibility study of applying laminar flow control to an lta vehicle. Final report. [Lighter than air vehicles  

SciTech Connect

The feasibility of applying laminar boundary-layer control with body shaping to a high altitude, Lighter-Than-Air vehicle was investigated. Solar-radiation-induced surface heating was shown to have a destablizing effect on laminar flow and caused the laminar flow to break down on regions of the vehicle surface exposed to high levels of solar radiation. Aerodynamic drag estimates were made for the vehicle. Surface waviness and roughness criteria for achieving laminar flow were determined.

Warner, D.J.; Ozgur, S.A.; Haigh, W.W.

1980-04-01

338

Suppression of Soot Formation and Shapes of Laminar Jet Diffusion Flames  

NASA Technical Reports Server (NTRS)

Laminar nonpremixed (diffusion) flames are of interest because they provide model flame systems that are far more tractable for analysis and experiments than practical turbulent flames. In addition, many properties of laminar diffusion flames are directly relevant to turbulent diffusion flames using laminar flamelet concepts. Finally, laminar diffusion flame shapes have been of interest since the classical study of Burke and Schumann because they involve a simple nonintrusive measurement that is convenient for evaluating flame shape predictions. Motivated by these observations, the shapes of round hydrocarbon-fueled laminar jet diffusion flames were considered, emphasizing conditions where effects of buoyancy are small because most practical flames are not buoyant. Earlier studies of shapes of hydrocarbon-fueled nonbuoyant laminar jet diffusion flames considered combustion in still air and have shown that flames at the laminar smoke point are roughly twice as long as corresponding soot-free (blue) flames and have developed simple ways to estimate their shapes. Corresponding studies of hydrocarbon-fueled weakly-buoyant laminar jet diffusion flames in coflowing air have also been reported. These studies were limited to soot-containing flames at laminar smoke point conditions and also developed simple ways to estimate their shapes but the behavior of corresponding soot-free flames has not been addressed. This is unfortunate because ways of selecting flame flow properties to reduce soot concentrations are of great interest; in addition, soot-free flames are fundamentally important because they are much more computationally tractable than corresponding soot-containing flames. Thus, the objectives of the present investigation were to observe the shapes of weakly-buoyant laminar jet diffusion flames at both soot-free and smoke point conditions and to use the results to evaluate simplified flame shape models. The present discussion is brief.

Xu, F.; Dai, Z.; Faeth, G. M.

2001-01-01

339

Estimation of the site of wheezes in pulmonary emphysema: airflow simulation study by the use of A 4D lung model.  

PubMed

Adventitious lung sounds in pulmonary emphysema, wheezes, are continuous musical sounds during expiration with 400 Hz or more. The textbook tells that expiratory airflow limitation in emphysema occurs at the peripheral airways and that wheezes are generated there. We have recently proposed a novel hypothesis based on image analysis and theoretical consideration that expiratory airflow limitation in emphysema occurs at the intra-mediastinal airway (trachea, main bronchi, and right lobar bronchi) due to compression by overinflated lungs. We performed expiratory airflow simulation by the use of a 4D finite element lung model, and found periodical vortex release with 300-900 Hz at the end of protrusion of the the tracheal posterior wall. Relationship between the peak frequency of pressure fluctuation and airflow velocity was in agreement with Strahal's law either in normal or emphysematous condition. Contrarily, airflow simulation in a small bronchus (1.5 mm in diameter) indicated no apparent periodic vortex release. PMID:24109720

Kitaoka, Hiroko; Cok, Salim

2013-01-01

340

A temperature-based variable for monitoring outdoor coil airflow in an air-source heat pump during frost-forming conditions  

SciTech Connect

Frost-buildup tests were conducted on a 3-ton (10.6kW) nominal cooling capacity air-source heat pump with an orifice expansion device. This study was conducted to determine if a simple temperature-based control variable could be used to determine the amount of degradation in the outdoor airflow (and heating capacity) of the unit. Refrigerant pressures and temperatures were monitored through-out the system in addition to power requirements and airflow rates. A temperature-based variable was developed that could be used to predict airflow degradation across the outdoor heat exchanger. This variable was defined using the difference between ambient air temperature and a measured refrigerant temperature. Eight refrigerant temperatures in the system were recorded and evaluated. Plots of airflow as a function of this temperature variable, along with plots of the absolute value percent changes of this temperature variable and airflow, were evaluated to determine which refrigerant temperatures could best be used in the variable to predict degradation in airflow. The best fit between the temperature-based variable and airflow degradation occurred with the inclusion of the refrigerant temperature at the outlet from the evaporator. Calculations of percent changes based on values sampled after a defrost showed a polynomial or linear relationship between airflow and the temperature-based variable. Data from two previously tested heat pumps were also used to compare changes in the outdoor airflow to changes in the temperature-based variable. The base-case heat pump and another heat pump both used an orifice as the expansion device in the heating mode. A third heat pump, which used a thermostatic expansion valve (TXV) as the expansion device in the heating mode, failed to show the same goodness of fit between airflow and the temperature-based variable.

Payne, W.V. II; O`Neal, D.L. [Texas A and M Univ., College Station, TX (United States). Energy Systems Lab.

1994-12-31

341

Thermal Induced Processes in Laminar System of Stainless Steel Beryllium  

NASA Astrophysics Data System (ADS)

The paper reports on investigation of the laminar system ‘stainless steel 12Cr18Ni10Ti Be’ at thermal treatment. There have been determined sequences of phase transformations along with relative amount of iron-containing phases in the samples subjected to thermal beryllization. It has been revealed that thermal beryllization of stainless steel thin foils results in ??? transformation and formation of the beryllides NiBe and FeBe2. It has also been revealed that direct ???- and reverse ???-transformations are accompanied by, correspondingly, formation and decomposition of the beryllide NiBe. It is shown that distribution of the formed phases within sample bulk is defined by local concentration of beryllium. Based on obtained experimental data there is proposed a physical model of phase transformations in stainless steel at thermal beryllization.

Zhubaev, A. K.; Kadyrzhanov, K. K.; Rusakov, V. S.; Turkebaev, T. E.

2005-07-01

342

Postfragmentation density function for bacterial aggregates in laminar flow  

NASA Astrophysics Data System (ADS)

The postfragmentation probability density of daughter flocs is one of the least well-understood aspects of modeling flocculation. We use three-dimensional positional data of Klebsiella pneumoniae bacterial flocs in suspension and the knowledge of hydrodynamic properties of a laminar flow field to construct a probability density function of floc volumes after a fragmentation event. We provide computational results which predict that the primary fragmentation mechanism for large flocs is erosion. The postfragmentation probability density function has a strong dependence on the size of the original floc and indicates that most fragmentation events result in clumps of one to three bacteria eroding from the original floc. We also provide numerical evidence that exhaustive fragmentation yields a limiting density inconsistent with the log-normal density predicted in the literature, most likely due to the heterogeneous nature of K. pneumoniae flocs. To support our conclusions, artificial flocs were generated and display similar postfragmentation density and exhaustive fragmentation.

Byrne, Erin; Bortz, David M.; Dzul, Steve; Solomon, Michael; Younger, John

2011-04-01

343

Flame height measurement of laminar inverse diffusion flames  

SciTech Connect

Flame heights of co-flowing cylindrical ethylene-air and methane-air laminar inverse diffusion flames were measured. The luminous flame height was found to be greater than the height of the reaction zone determined by planar laser-induced fluorescence (PLIF) of hydroxyl radicals (OH) because of luminous soot above the reaction zone. However, the location of the peak luminous signals along the centerline agreed very well with the OH flame height. Flame height predictions using Roper's analysis for circular port burners agreed with measured reaction zone heights when using values for the characteristic diffusion coefficient and/or diffusion temperature somewhat different from those recommended by Roper. The fact that Roper's analysis applies to inverse diffusion flames is evidence that inverse diffusion flames are similar in structure to normal diffusion flames. (author)

Mikofski, Mark A. [Microgravity Combustion Laboratory, University of California, Berkeley, CA 94720 (United States); Williams, Timothy C.; Shaddix, Christopher R.; Blevins, Linda G. [Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94550 (United States)

2006-07-15

344

Flame height measurement of laminar inverse diffusion flames.  

SciTech Connect

Flame heights of co-flowing cylindrical ethylene-air and methane-air laminar inverse diffusion flames were measured. The luminous flame height was found to be greater than the height of the reaction zone determined by planar laser-induced fluorescence (PLIF) of hydroxyl radicals (OH) because of luminous soot above the reaction zone. However, the location of the peak luminous signals along the centerline agreed very well with the OH flame height. Flame height predictions using Roper's analysis for circular port burners agreed with measured reaction zone heights when using values for the characteristic diffusion coefficient and/or diffusion temperature somewhat different from those recommended by Roper. The fact that Roper's analysis applies to inverse diffusion flames is evidence that inverse diffusion flames are similar in structure to normal diffusion flames.

Shaddix, Christopher R.; Williams, Timothy C.; Blevins, Linda Gail; Mikofski, Mark A. (University of California Berkeley)

2005-09-01

345

Laminar boundary-layer solutions in three dimensions  

NASA Technical Reports Server (NTRS)

As an alternative to pure finite-difference techniques, the Method of Integral Relations (MIR) is formulated for three-dimensional boundary-layer flows with separation, and applied to two problems. The first concerns an incompressible laminar flow over a plate with an attached cylinder, where the potential solution of the flow round the circular cylinder is used as the boundary condition. In the second application the solution to the three-dimensional boundary-layer flow over blunt bodies is discussed and results for an ellipsoid of revolution at 30 deg incidence are presented. In both cases the results are found to be in satisfactory agreement with those obtained by finite-difference methods.

Modarress, D.; Holt, M.

1976-01-01

346

Parameter-uniform numerical methods for a laminar jet problem  

NASA Astrophysics Data System (ADS)

We consider the classical problem of a two-dimensional laminar jet of incompressible fluid flowing into a stationary medium of the same fluid. The equations of motion are the same as the boundary layer equations for flow past an infinite flat plate, but with different boundary conditions. Numerical experiments show that, using appropriate piecewise-uniform meshes, numerical solutions together with their scaled discrete derivatives are obtained which are parameter (i.e., viscosity ) robust with respect to both the number of mesh nodes and the number of iterations required for convergence. While the method employed is non-conservative, we show with the aid of numerical experiments that the loss in conservation of momentum is minimal.

Ansari, Ali R.; Hegarty, Alan F.; Shishkin, Grigori I.

2003-11-01

347

Shapes of buoyant and nonbuoyant laminar jet diffusion flames  

SciTech Connect

Flame shapes were measured for buoyant and nonbuoyant laminar gas jet diffusion flames burning, methane, ethane, and propane in quiescent air. Test conditions involved burner diameters of 0.19--5.5 mm, ambient pressures of 0.25--2 atm, and fuel flowrates of 0.04--4.6 mg/s. Care was taken to minimize interference from soot emissions and from ignition disturbances. Microgravity conditions were obtained in the 2.2-s drop tower at the NASA Lewis Research Center. Normalized lengths of both buoyant and nonbuoyant flames were proportional to source Reynolds number, but the nonbuoyant flames were 40% longer on average. Normalized widths of the nonbuoyant flames were constant for Re {ge} 100, whereas buoyant flame widths scaled with source Froude number. Several nonbuoyant flame models are evaluated with the present shape data.

Sunderland, P.B. [National Research Council, Cleveland, OH (United States)] [National Research Council, Cleveland, OH (United States); Mendelson, B.J. [Princeton Univ., NJ (United States). Dept. of Mechanical and Aerospace Engineering] [Princeton Univ., NJ (United States). Dept. of Mechanical and Aerospace Engineering; Yuan, Z.G. [National Center for Microgravity Research, Cleveland, OH (United States)] [National Center for Microgravity Research, Cleveland, OH (United States); Urban, D.L. [NASA Lewis Research Center, Cleveland, OH (United States)] [NASA Lewis Research Center, Cleveland, OH (United States)

1999-02-01

348

Metal-metal laminar composites for high temperature applications  

NASA Technical Reports Server (NTRS)

A study was conducted to obtain indications of the potentialities of laminar metal-metal composites for elevated temperature use. Most of the composites consisted of multiple layers or laminae of tungsten alternated with laminae of Nichrome V, a ductile, weaker but oxidation-resistant alloy. Composites with 50 volume percent of each phase were tested in tension and stress rupture at temperatures of 871 and 1093 C (1600 and 2000 F) and in impact at 23 and 524 C (73 and 975 F). A tension and a short time stress-rupture test was conducted on specimens of 77 v/o W-Re-Hf-C/23 v/o Inconel alloy 600 at 1093 C (2000 F).

Hoffman, C. A.; Weeton, J. W.

1972-01-01

349

Computational wing design studies relating to natural laminar flow  

NASA Technical Reports Server (NTRS)

Two research studies are described which directly relate to the application of natural laminar flow (NLF) technology to transonic transport-type wing planforms. Each involved using state-of-the-art computational methods to design three-dimensional wing contours which generate significant runs of favorable pressure gradients. The first study supported the Variable Sweep Transition Flight Experiment and involves design of a full-span glove which extends from the leading edge to the spoiler hinge line on the upper surface of an F-14 outer wing panel. A wing was designed computationally for a corporate transport aircraft in the second study. The resulting wing design generated favorable pressure gradients from the leading edge aft to the mid-chord on both upper and lower surfaces at the cruise design point. Detailed descriptions of the computational design approach are presented along with the various constraints imposed on each of the designs.

Waggoner, Edgar G.

1986-01-01

350

Active feedback control achieving sub-laminar skin friction drag  

NASA Astrophysics Data System (ADS)

Effects of an idealized feedback control are studied by means of direct numerical simulation (DNS). The control input is a body force directly suppressing the Reynolds shear stress near the wall. Namely, the body force is applied in the wall-normal direction and in phase with the streamwise velocity fluctuation. The DNS of turbulent pipe flow at constant flow rate at Re_b=5300 (i.e, Re_?? 180 for uncontrolled flow) shows that the skin friction can be reduced even to a sub-laminar level. This is caused by the reversal of the sign of Reynolds shear stress, which results in a negative value of ``the turbulent contribution to skin friction'' [Fukagata et al., Phys. Fluids 14, L73 (2002)]. The turbulence structure is also drastically modified with this control. The quasi-streamwise vortices completely vanished and alternating spanwise roller-like structures formed instead.

Fukagata, Koji; Kasagi, Nobuhide

2004-11-01

351

The simulation of coherent structures in a laminar boundary layer  

NASA Technical Reports Server (NTRS)

Coherent structures in turbulent shear flows were studied extensively by several techniques, including the VITA technique which selects rapidly accelerating or decelerating regions in the flow. The evolution of a localized disturbance in a laminar boundary layer shows strong similarity to the evolution of coherent structures in a turbulent-wall bounded flow. Starting from a liftup-sweep motion, a strong shear layer develops which shares many of the features seen in conditionally-sampled turbulent velocity fields. The structure of the shear layer, Reynolds stress distribution, and wall pressure footprint are qualitatively the same, indicating that the dynamics responsible for the structure's evolution are simple mechanisms dependent only on the presence of a high mean shear and a wall and independent of the effects of local random fluctuations and outer flow effects. As the disturbance progressed, the development of streak-like-high- and low-speed regions associated with the three-dimensionality.

Breuer, Kenny; Landahl, Marten T.; Spalart, Philippe R.

1987-01-01

352

Metal-metal laminar composites for high-temperature applications.  

NASA Technical Reports Server (NTRS)

A study was conducted to obtain indications of the potentialities of laminar metal-metal composites for elevated-temperature use. Most of the composites consisted of multiple layers or laminae of tungsten alternated with laminae of Nichrome V, a ductile, weaker, but oxidation-resistant alloy. Composites with 50 vol % of each phase made from 0.0025 cm, 0.0125 cm, or 0.050 cm laminae, were tested in tension and stress rupture at temperatures of 871 and 1093 C and in impact at 23 and 524 C. A tension and a short-time stress-rupture test was conducted on specimens of 77 vol % W-Re-Hf-C/23 vol % Inconel Alloy 600 at 1093 C.

Hoffman, C. A.; Weeton, J. W.

1973-01-01

353

Laminar separation control effects of shortfin mako shark skin  

NASA Astrophysics Data System (ADS)

Shark skin is investigated as a means of laminar flow separation control due to its preferential flow direction as well as the potential for scales to erect and obstruct low-momentum backflow resulting from an adverse pressure gradient acting on the boundary layer. In this study, the effect of the scales on flow reversal is observed in laminar flow conditions. This is achieved by comparing the flow over a pectoral fin from a shortfin mako shark to that over the same fin that is painted to neutralize the effect of the scales on the flow. The effect of the scales on flow reversal is also observed by comparing the flow over a smooth PVC cylinder to that over the same cylinder with samples of mako shark skin affixed to the entire circumference of the cylinder. These samples were taken from the flank region of the shark because the scales at this location have been shown to have the greatest angle of erection compared to the scales on the rest of the shark's body. Scales at this location have an average crown length of 220 microm with a maximum bristling angle of proximately 50 degrees. Because these scales have the highest bristling angle, they have the best potential for separation control. All data was taken using time-resolved Digital Particle Image Velocimetry. The flow over the pectoral fin was analyzed at multiple angles of attack. It was found that the shark skin had the effect of decreasing the size of the separated region over both the pectoral fin and the cylinder as well as decreasing the magnitudes of the reversing flow found in these regions. For all Reynolds numbers tested, drag reduction over 28% was found when applying the sharkskin to the cylinder.

Bradshaw, Michael Thomas

354

Forced response of a laminar shock-induced separation bubble  

NASA Astrophysics Data System (ADS)

The source of unsteadiness in shock-wave/boundary-layer interactions is currently disputed. This paper considers a two-dimensional separation bubble induced by an oblique shock wave interacting with a laminar boundary layer at a free-stream Mach number of 1.5. The global response of the separated region to white noise forcing is analyzed for different interaction strengths, which generate small and large separation bubbles. Forcing location and amplitude effects have been examined. For both interaction strengths and for forcing both upstream and inside the bubble, the wall-pressure spectra downstream of the separation show a high-frequency peak that is demonstrated to be a Kelvin-Helmholtz instability. A low-frequency response at the separation point is also found when the separation bubble is only forced internally, therefore with a disturbance-free upstream boundary layer. For low-amplitude internal forcing, the low-frequency response at the separation point and downstream of the bubble is linear. However, when forced upstream the low-frequency unsteadiness of the large separation bubble is found to be driven by nonlinearities coming from the downstream shedding. The same nonlinear behavior is found when the separation bubble is internally forced over a narrow band around the shedding frequency, without low-frequency disturbances. This analysis for a laminar interaction is used to interpret the low-frequency unsteadiness found at the foot of the shock of turbulent interactions. Here, the low-frequency unsteadiness occurs in the absence of upstream disturbances and a linear relationship is found between the internal forcing and the response near the separation point. When low-frequencies are not present in the forcing they are generated from weak nonlinearities of the shear-layer instability modes.

Sansica, A.; Sandham, N. D.; Hu, Z.

2014-09-01

355

Numerical Prediction of Laminar Instability Noise for NACA 0012 Aerofoil  

NASA Astrophysics Data System (ADS)

Aerofoil self-generated noise is recognized to be of fundamental importance in the frame of applied aeroacoustics and the use of computational methods to assess the acoustic behaviour of airframe components challenges an even larger community of engineers and scientists. Several noise generation mechanisms can be found which are mainly related to the physical development of turbulence over the boundary layer. They can be classified in 3 main categories: the Turbulent Boundary Layer—Trailing Edge noise (TBL-TE), the Laminar Boundary Layer—Vortex Shedding (LBL-VS) noise and the Separation Stall (S-S) noise. The TBL-TE is mainly related to the noise generated by turbulent eddies which develop into the boundary layer and usually exhibits a broadband spectrum. The LBL-VS is related to laminar instabilities that can occur within the boundary layer which are responsible for a very late transition and generate a typical peaked tonal noise, while the S-S noise mainly results from the development of large vortices after the separation point. In this paper we propose a numerical analysis targeted to the simulation the LBL-VS noise mechanisms on a NACA 0012 aerofoil, tested at a Reynolds number of 1.1 M and Mach number of 0.2. The aerodynamic simulation is performed with a 2D transient RANS approach using the k-? transitional turbulence model, while the acoustic computations are performed with the FfowcsWilliams-Hawkings (FW-H) acoustic analogy and with a Finite Element (FE) approach solving Lighthill's wave equation. Computed noise spectra are compared with experimental data published by NASA showing a good agreement both for peak location as well as for the predicted noise level.

De Gennaro, Michele; Hueppe, Andreas; Kuehnelt, Helmut; Kaltenbacher, Manfred

2011-09-01

356

Regional airflow and particle distribution in the lung with a 3D-1D coupled subject-specific boundary condition  

NASA Astrophysics Data System (ADS)

Correct prediction of regional distribution of inhaled aerosol particles is vital to improve pulmonary medicine. Physiologically consistent regional ventilations of airflow and aerosol particles are simulated with a 3D-1D coupled subject-specific boundary condition (BC). In 3D CT-resolved 7-generation airways, large eddy simulations are performed to capture detailed airflow characteristics and Lagrangian particle simulations are carried to track the particle transport and deposition. Results are compared with two traditional outlet BCs: uniform velocity and uniform pressure. Proposed BC is eligible for physiologically consistent airflow distribution in the lung, while the others are not. The regional ventilation and deposition of particles reflect the regional ventilation of airflow. In this study, two traditional BCs yield up to 98% (334%) over-prediction in lobar particle ventilation (deposition) fraction. Upper to lower particle ventilation ratios of both left and right lungs read ˜0.4 with the proposed BC, while those for the other two BCs vary with the error up to 73%.

Choi, Jiwoong; Yin, Youbing; Hoffman, Eric; Tawhai, Merryn; Lin, Ching-Long

2010-11-01

357

Experimental and Numerical Study on Effects of Airflow and Aqueous Ammonium Solution Temperature on Ammonia Mass Transfer Coefficient  

Microsoft Academic Search

This paper reports the results of an investigation, based on fundamental fluid dynamics and mass transfer theory, carried out to obtain a general understanding of ammonia mass transfer from an emission surface. The effects of airflow and aqueous ammonium solution temperature on ammonia mass transfer are investigated by using computational fluid dynamics (CFD) modeling and by a mechanism modeling using

Li Rong; Peter V. Nielsen; Guoqiang Zhang; Glauber Mariano; Ani Torres; Wellington Jesus; Walter Nakaema; Maria Jorge; Rauda Mariani; Klara Slezakova; Dionísia Castro; Maria Pereira; Simone Morais; Cristina Delerue-Matos; Maria Alvim-Ferraz; Catherine Barton; Charles Zarzecki; Mark Russell; Marjaleena Aatamila; Pia Verkasalo; Maarit Korhonen; Marja Viluksela; Kari Pasanen; Pekka Tiittanen; Aino Nevalainen; Yi-Ming Kuo; Juu-En Chang; Kun-Yu Chang; Chih-C. Chao; Yeu-Juin Tuan; Guo-Ping Chang-Chien; Yongping Li; Guohe Huang; Arhontoula Chatzilazarou; Evangelos Katsoyannos; Olga Gortzi; Stavros Lalas; Yiannis Paraskevopoulos; Euthalia Dourtoglou; John Tsaknis; Tarek Abichou; Jeremy Clark; Sze Tan; Jeffery Chanton; Gary Hater; Roger Green; Doug Goldsmith; Morton Barlaz; Nathan Swan; Gang Sun; Huiqing Guo; Jonathan Peterson; Zhengmin Qian; Hung-Mo Lin; Walter Stewart; Nirav Shah; Linli Kong; Fen Xu; Denjin Zhou; Zhicao Zhu; Qingci He; Shengwen Liang; Weiqing Chen; Chungsying Lu; Hsunling Bai; Fengsheng Su; Wenfa Chen; Jyh Hwang; Hsiu-Hsia Lee; Judith Chow; John Watson; Douglas Lowenthal; Lung-Wen Chen; Nehzat Motallebi

2010-01-01

358

What causes atmospheric airflow and wind? Why exactly is it that arches create support for structures like bridges? How  

E-print Network

What causes atmospheric airflow and wind? Why exactly is it that arches create support mass because of molecule movements? If not, can we explain in terms of surface tension? What is chaos theory? What is the difference between AC and DC? What are the differences between Van der Graff machines

Redner, Sidney

359

Partial Reversibility of Airflow Limitation and Increased Exhaled NO and Sputum Eosinophilia in Chronic Obstructive Pulmonary Disease  

Microsoft Academic Search

We investigated the relationship between the reversibility of air- flow limitation, the concentration of nitric oxide (NO) in exhaled air, and the inflammatory cells in the sputum of patients with sta- ble chronic obstructive pulmonary disease (COPD). We examined nine normal healthy control subjects and 20 nonatopic patients with COPD. Ten patients had no reversibility of airflow limitation (increase in

ALBERTO PAPI; MICAELA ROMAGNOLI; SIMONETTA BARALDO; FAUSTO BRACCIONI; IPPOLITO GUZZINATI; MARINA SAETTA; ADALBERTO CIACCIA; LEONARDO M. FABBRI

2000-01-01

360

The Body-Mass Index, Airflow Obstruction, Dyspnea, and Exercise Capacity Index in Chronic Obstructive Pulmonary Disease  

Microsoft Academic Search

background Chronic obstructive pulmonary disease (COPD) is characterized by an incompletely re- versible limitation in airflow. A physiological variable — the forced expiratory volume in one second (FEV 1 ) — is often used to grade the severity of COPD. However, patients with COPD have systemic manifestations that are not reflected by the FEV 1 . We hypoth- esized that

Bartolome R. Celli; Claudia G. Cote; Jose M. Marin; Ciro Casanova; Maria Montes de Oca; Reina A. Mendez; Victor Pinto Plata; Howard J. Cabral

2004-01-01

361

Airflow-terrain interactions through a mountain gap, with an example of eolian activity beneath an atmospheric hydraulic jump  

SciTech Connect

The integration of atmospheric soundings from a fully instrumented aircraft with detailed sedimentary and geomorphic analyses of eolian features in the Ferris dune field of south-central Wyoming lends insight into the manner in which topography interacts with airflow to modify eolian activity. Topographically modified airflow results in zones of airflow deceleration, acceleration, and enhanced atmospheric turbulence, all of which influence the surface morphology and sedimentology. Extreme lateral confluence of prevailing airflow produces accelerated, unidirectional winds. These winds correlate with unusually continuous and elongate parabolic dunes that extend into a mountain gap (Windy Gap). Persistently heightened winds produced at the entrance to Windy Gap have resulted in a concentration of active sand dunes that lack slipfaces. Common development of a strongly amplified atmospheric wave analogous to a hydraulic jump in the gap contributes to the formation of a variety of eolian features that mantle the surface of Windy Gap and the Ferris dune field tail. Heightened, unidirectional winds in this zone promote grain-size segregation, the formation of elongated and aligned sand drifts, climbing and falling dunes, elongate scour streaks, and parabolic dunes that have low-angle (< 20/sup 0/) cross-stratification. Deflation of bedrock and loose sediment has been enhanced in the zone of maximum turbulence beneath the hydraulic jump.

Gaylord, D.R.; Dawson, P.J.

1987-09-01

362

Airflow calibration and exhaust pressure/temperature survey of an F404, S/N 215-109, turbofan engine  

NASA Technical Reports Server (NTRS)

A General Electric F-404 turbofan engine was calibrated for thrust and airflow at the NASA Lewis Propulsion System Laboratory in support of future flight tests of the X-29 aircraft. Tests were conducted with and without augmentation, over a range of flight conditions, including the two design points of the airplane. Data obtained during the altitude tests will be used to correct two independent gross thrust calculation routines which will be installed and operated on the airplane to determine in-flight gross thrust. Corrected airflow data as a function of corrected fan speed collapsed onto a single curve. Similarly, trends were observed and defined for both augmented and dry thrust. Overall agreement between measured data and F-404 Engine Spec Deck data was within 2 percent for airflow and 6 percent for thrust. The results of an uncertainty analysis for thrust and airflow is presented. In addition to the thrust calibration, the exhaust gas boundary layer pressure and temperatures were surveyed at selected condition and engine power levels to obtain data for another NASA F-404 program. Test data for these surveys are presented.

Burns, Maureen E.; Kirchgessner, Thomas A.

1987-01-01

363

Regulating glottal airflow in phonation: Application of the maximum power transfer theorem to a low dimensional phonation model  

Microsoft Academic Search

Two competing views of regulating glottal airflow for maximum vocal output are investigated theoretically. The maximum power transfer theorem is used as a guide. A wide epilarynx tube (laryngeal vestibule) matches well with low glottal resistance (believed to correspond to the ``yawn-sigh'' approach in voice therapy), whereas a narrow epilarynx tube matches well with a higher glottal resistance (believed to

Ingo R. Titze

2002-01-01

364

Unsteady thermal performance analysis of a room with serial and parallel duct radiant floor heating system using hot airflow  

Microsoft Academic Search

In this study, the unsteady thermal performance of a test room heated by circulating hot airflow under the floor was analyzed with a developed mathematical model based on heat transfer equilibrium among the air flow, the floor and the indoor air. The time variations in the indoor air temperature for the serial duct floor heating system were investigated theoretically and

O?uz Bozk?r; Suat Canbazo?lu

2004-01-01

365

Cfd analysis and airflow measurements to approach large industrial halls energy efficiency: A case study of a cardboard mill hall  

Microsoft Academic Search

This paper deals with numerical methods for predicting air flow patterns in large industrial halls. Some major findings of the investigation of the airflow patterns in paper machine hall of Umka Cardboard Mill are presented in the paper. The main reason for the interest in this problem is to find optimal locations for extract air intake connections of the ventilation

Nikola Tanasi?; Goran Jankes; Håkon Skistad

2011-01-01

366

Wireless communication in the airflow verification system of biological safety cabinet  

NASA Astrophysics Data System (ADS)

In recent years, biological safety cabinet has been applied widely and urgently to the biochemistry laboratory. An increasing research need has been asked about the processing safety of the workers. In this safety cabinet system, among series of related factors, the main parameter is airflow velocity. At percent, this measuring work is usually done by processional workers, thus leading to the low efficiency and disadvantages. In this paper, a new method was approved to deal with the current problem, where wireless communication controller and detector. According to the experimental data and the comparison between the two methods, the wireless way is more convenient and more efficient than previous one, and the working distance can be about 730 meters. Meanwhile, the communication system has already been used in Guangzhou Institute of Metrology Laboratory.

Zhang, Yu-de; Hou, De-xin; Qiu, Jian; Ye, Shu-liang

2013-01-01

367

Development of PIV techniques to measure airflow patterns in ventilated airspaces  

SciTech Connect

A measurement technique based on particle image velocimetry (PIV) to measure quantitatively airflow patterns and distribution in ventilated airspaces is presented. Air laden with helium-filled bubbles was illuminated by a two-dimensional light sheet in a full-scale ventilated room. Images of bubbles visualized in the light sheet were recorded using a photographic camera. Relatively long camera exposure time makes it possible to record the bubble path in the designed time period. Image-shift techniques remove the directional ambiguity. The photographic images were scanned into a computer, and the digitized images were processed automatically using an image-processing program to extract flow-field velocity information. The configuration, working principles, sample results, accuracy, capability, and limitations of the technique are discussed in this paper. This measurement method is part of a larger study of aerosol spatial distribution, ventilation effectiveness, and aerial contaminant control strategies.

Zhao, L.; Zhang, Y.; Wang, X.; Riskowski, G.L.; Christianson, L.L.

1999-07-01

368

Numerical investigation of airflow in an idealized human extra-thoracic airway: a comparison study.  

PubMed

Large eddy simulation (LES) technique is employed to numerically investigate the airflow through an idealized human extra-thoracic airway under different breathing conditions, 10, 30, and 120 l/min. The computational results are compared with single and cross hot-wire measurements, and with time-averaged flow field computed by standard [Formula: see text] and [Formula: see text]-SST Reynolds-averaged Navier-Stokes (RANS) models and the Lattice Boltzmann method (LBM). The LES results are also compared to root-mean-square (RMS) flow field computed by the Reynolds stress model (RSM) and LBM. LES generally gives better prediction of the time-averaged flow field than RANS models and LBM. LES also provides better estimation of the RMS flow field than both the RSM and the LBM. PMID:23619907

Chen, Jie; Gutmark, Ephraim

2014-01-01

369

Unsteady laryngeal airflow simulations of the intra-glottal vortical structures  

PubMed Central

The intra-glottal vortical structures developed in a static divergent glottis with continuous flow entering the glottis are characterized. Laryngeal airflow calculations are performed using the Large Eddy Simulation approach. It has been shown that intra-glottal vortices are formed on the divergent wall of the glottis, immediately downstream of the separation point. Even with non-pulsatile flow entering the glottis, the vortices are intermittently shed, producing unsteady flow at the glottal exit. The vortical structures are characterized by significant negative static pressure relative to the ambient pressure. These vortices increase in size and strength as they are convected downstream by the flow due to the entrained air from the supra-glottal region. The negative static pressures associated with the intra-glottal vortical structures suggest that the closing phase during phonation may be accelerated by such vortices. The intra-glottal negative pressures can affect both vocal fold vibration and voice production. PMID:20058989

Mihaescu, Mihai; Khosla, Sid M.; Murugappan, Shanmugam; Gutmark, Ephraim J.

2010-01-01

370

Inter-flat airflow and airborne disease transmission in high-rise residential buildings.  

PubMed

1. A virus-spread mechanism is related to inter-flat or interzonal airflow through open windows caused by buoyancy effects. 2. Both on-site measurements and numerical simulations quantify the amount of the exhaust air that exits the upper part of the window of a floor and re-enters the lower part of the open window of the immediately upper floor. 3. Ventilation air could contain up to 7% (in terms of mass fraction) of the exhaust air from the lower floor.4. In high-rise buildings, windows flush with the façade are a major route for the vertical spread of pathogen-containing aerosols, especially those<1 ?m in diameter. PMID:22311361

Niu, J; Tung, C W; Gao, N

2012-02-01

371

Numerical investigation of airflow in an idealised human extra-thoracic airway: a comparison study  

PubMed Central

Large eddy simulation (LES) technique is employed to numerically investigate the airflow through an idealised human extra-thoracic airway under different breathing conditions, 10 l/min, 30 l/min, and 120 l/min. The computational results are compared with single and cross hot-wire measurements, and with time-averaged flow field computed by standard k-? and k-?-SST Reynolds averaged Navier-Stokes (RANS) models and the Lattice-Boltzmann method (LBM). The LES results are also compared to root-mean-square (RMS) flow field computed by the Reynolds stress model (RSM) and LBM. LES generally gives better prediction of the time-averaged flow field than RANS models and LBM. LES also provides better estimation of the RMS flow field than both the RSM and the LBM. PMID:23619907

Chen, Jie; Gutmark, Ephraim

2013-01-01

372

Effect of airflow on house fly (Diptera: Muscidae) distribution in poultry houses.  

PubMed

Numbers of fecal and vomit spots deposited by house flies, Musca domestica L., on spot cards were about twice as high on cards placed on the downwind sides as on the upwind sides of building support posts in caged-layer poultry houses with tunnel ventilation in Brooksville, FL. This trend was stronger at the ends of the houses where airflow is faster than in the relatively still-air center of the houses. A similar evaluation conducted in a pullet house (Zephyrhills, FL) with an evaporative cooling ventilation system revealed significantly higher fly counts on spot cards and sticky cards in downwind compared with upwind orientations. Flies in the pullet house were concentrated in both ends of the house and in the center, with comparatively fewer flies in the intermediate regions. There was a high degree of correlation between spot card and sticky card counts in the pullet house. PMID:10333752

Geden, C J; Hogsette, J A; Jacobs, R D

1999-04-01

373

Response characteristics for thermal and pressure devices commonly used for monitoring nasal and oral airflow during sleep studies.  

PubMed

We examined thermocouple and pressure cannulae responses to oral and nasal airflow using a polyester model of a human face, with patent nasal and oral orifices instrumented with a dual thermocouple (F-ONT2A, Grass) or a dual cannula (0588, Braebon) pressure transducer (± 10 cm H2O, Celesco) system. Tidal airflow was generated using a dual compartment facemask with pneumotachographs (Fleisch 2) connected to the model orifices. During nasal breathing: thermocouple amplitude = 0.38 Ln [pneumotachograph amplitude] + 1.31 and pressure cannula amplitude = 0.93 [pneumotachograph amplitude](2.15); during oral breathing: thermocouple amplitude = 0.44 Ln [pneumotachograph amplitude] + 1.07 and pressure cannula amplitude = 0.33 [pneumotachograph amplitude](1.72); (all range ? 0.1-? 4.0 L s(-1); r(2) > 0.7). For pneumotachograph amplitudes <1 L s(-1) (linear model) change in thermocouple amplitude/unit change in pneumotachograph amplitude was similar for nasal and oral airflow, whereas nasal pressure cannula amplitude/unit change in pneumotachograph amplitude was almost four times that for oral. Increasing oral orifice area from 0.33 cm(2) to 2.15 cm(2) increased oral thermocouple amplitude/unit change in pneumotachograph amplitude by ? 58% but decreased pressure cannula amplitude/unit change in pneumotachograph amplitude by 49%. For pneumotachograph amplitudes up to 1 L s(-1), alterations in inspiratory/expiratory ratios or total respiratory time did not affect the sensitivity of either nasal or oral pressure cannulae or the nasal thermocouple, but the oral thermocouple sensitivity was influenced by respiratory cycle time. Different nasal and oral responses influence the ability of these systems to quantitatively assess nasal and oral airflow and oro-nasal airflow partitioning. PMID:24557006

Gehring, J M; Cho, J-G; Wheatley, J R; Amis, T C

2014-03-01

374

Envelope Analysis of the Airflow Signal To Improve Polysomnographic Assessment of Sleep Disordered Breathing  

PubMed Central

Study Objectives: Given the detailed respiratory waveform signal provided by the nasal cannula in polysomnographic (PSG) studies, to quantify sleep breathing disturbances by extracting a continuous variable based on the coefficient of variation of the envelope of that signal. Design: Application of an algorithm for envelope analysis to standard nasal cannula signal from actual polysomnographic studies. Setting: PSG recordings from a sleep disorders center were analyzed by an algorithm developed on the Igor scientific data analysis software. Patients or Participants: Recordings representative of different degrees of sleep disordered breathing (SDB) severity or illustrative of the covariation between breathing and particularly relevant factors and variables. Interventions: The method calculated the coefficient of variation of the envelope for each 30-second epoch. The normalized version of that coefficient was defined as the respiratory disturbance variable (RDV). The method outcome was the all-night set of RDV values represented as a time series. Measurements and Results: RDV quantitatively reflected departure from normal sinusoidal breathing at each epoch, providing an intensity scale for disordered breathing. RDV dynamics configured itself in recognizable patterns for the airflow limitation (e.g., in UARS) and the apnea/hypopnea regimes. RDV reliably highlighted clinically meaningful associations with staging, body position, oximetry, or CPAP titration. Conclusions: Respiratory disturbance variable can assess sleep breathing disturbances as a gradual phenomenon while providing a comprehensible and detailed representation of its dynamics. It may thus improve clinical diagnosis and provide a revealing descriptive tool for mechanistic sleep disordered breathing modeling. Respiratory disturbance variable may contribute to attaining simplified screening methodologies, novel diagnostic criteria, and insightful research tools. Citation: Díaz JA; Arancibia JM; Bassi A; Vivaldi EA. Envelope analysis of the airflow signal to improve polysomnographic assessment of sleep disordered breathing. SLEEP 2014;37(1):199-208. PMID:24470709

Díaz, Javier A.; Arancibia, José M.; Bassi, Alejandro; Vivaldi, Ennio A.

2014-01-01

375

Phonation threshold pressure estimation using electroglottography in an airflow redirection system  

PubMed Central

Objectives/Hypothesis The present study proposed to estimate phonation threshold pressure (PTP) non-invasively using airflow redirection into a pneumatic capacitance system. Study Design Prospective study. Methods Subjects phonated into the device, which interrupts airflow mechanically and redirects the flow into a pneumatic capacitor. Five interruptions were effected per trial. PTP was estimated as the difference between subglottal pressure (SGP) and transglottal pressure at phonation offset. The novel method was tested for consistency in 20 normal human subjects at low (75 dB) and high (85 dB) sound pressure levels. The device was tested for validity on a tracheotomy patient. Results Mean SGP was 9.02 ± 3.27 cm H2O and mean PTP was 3.68 ± 1.41 cm H2O. Intrasubject coefficient of variation, a measure of intrasubject consistency, was 0.33 ± 0.23. Statistically significant differences existed between the means of SGP but not PTP at 75 dB and 85 dB. The correlation coefficient between accepted and experimental SGP in a tracheotomy patient was 0.947 (p<0.001). Conclusions Measurements corresponded well to previously reported values, and intrasubject variability was low, indicating the device was consistent. Testing on a tracheotomy patient demonstrated validity. More research is needed to determine the sensitivity and specificity of the device in differentiating between normal and pathological voices. This device may have clinical application as a non-invasive and reliable method of estimating PTP and indicating that laryngeal health is likely abnormal. PMID:19688842

Rieves, Adam L.; Regner, Michael F.; Jiang, Jack J.

2009-01-01

376

Respiratory-triggered electron beam CT with integrated spirometry for evaluation of dynamic airflow  

NASA Astrophysics Data System (ADS)

The purpose is to integrate time-attenuation curves from Electron-Beam CT with flow-time curves from spirometry in the analysis of airflow obstruction. A pressure-sensitive switch was connected between a spirometer mouthpiece and a modified EBCT scanner keyboard. The onset of expiratory flow causes pressure changes which simultaneously trigger EBCT and spirometric acquisitions. Subjects performed a forced expiratory maneuver, during which EBCT images of the lung were obtained every 500 ms using 130 kVp, 630 mA, 100 ms scan time and 3 mm collimation. From EBCT images, time-attenuation curves were generated for each of three zones (non-dependent, middle and dependent lung) using small ROIs (12 mm2) placed over approximately the same anatomic regions of lung. The resulting time- attenuation curves and flow-time curves were then superimposed. Two normal subjects, two subjects with emphysema and three lung transplant subjects have been studied to date. In normal subjects, lung attenuation increases steadily during the first 4 - 6 seconds of expiration, whereas in patients with emphysema, lung attenuation was relatively constant over the course of expiration. Lung transplant subjects show both of these characteristics--normal characteristics for the transplant lung and emphysematous characteristics for the native lung. Lung transplant subjects may also demonstrate some dynamics between transplant and diseased lung. Respiratory-triggered EBCT can be used to simultaneously acquire time-attenuation and flow-time data. This has been used to characterize dynamic airflow patterns in patients with respiratory disease.

McNitt-Gray, Michael F.; Goldin, Jonathan G.; Welch, Mike; Szold, Oded; Levine, Michael; Aberle, Denise R.

1996-04-01

377

A Study of Laminar Separation Bubble in the Concave Region of an Airfoil Using Laser Velocimetry  

NASA Technical Reports Server (NTRS)

Laser velocimetry (LV) was used to study the nature of laminar separation bubbles in the concave region of a 1.83-meter airfoil model which was tested in the NASA Langley Low Turbulence Pressure Tunnel. Three component, coincident data from LV measurements including histograms of particle velocity, mean velocity profiles, turbulence intensity, and Reynolds stresses within the shear layer were used to determine the locations of laminar separation, transition, and turbulent reattachment. Boundary-layer parameters determined from velocity profiles were used to compare the results with existing empirical relations for describing the laminar separation bubble.

Mangalam, Sivaramakrishnan; Meyers, James F.; Dagenhart, John R.; Harvey, William D.

1985-01-01

378

A study of laminar separation bubble in the concave region of an airfoil using laser velocimetry  

NASA Technical Reports Server (NTRS)

Laser velocimetry (LV) was used to study the nature of laminar separation bubbles in the concave region of a 1.83-meter airfoil model which was tested in the NASA Langley Low Turbulence Pressure Tunnel. Three component, coincident data from LV measurements including histograms of particle velocity, mean velocity profiles, turbulence intensity, and Reynolds stresses within the shear layer were used to determine the locations of laminar separation, transition, and turbulent reattachment. boundary-layer parameters determined from velocity profiles were used to compare the results with existing empirical relations for describing the laminar separation bubble.

Mangalam, S. M.; Meyers, J. F.; Dagenhart, J. R.; Harvey, W. D.

1985-01-01

379

Summary of past experience in natural laminar flow and experimental program for resilient leading edge  

NASA Technical Reports Server (NTRS)

The potential of natural laminar flow for significant drag reduction and improved efficiency for aircraft is assessed. Past experience with natural laminar flow as reported in published and unpublished data and personal observations of various researchers is summarized. Aspects discussed include surface contour, waviness, and smoothness requirements; noise and vibration effects on boundary layer transition, boundary layer stability criteria; flight experience with natural laminar flow and suction stabilized boundary layers; and propeller slipstream, rain, frost, ice and insect contamination effects on boundary layer transition. The resilient leading edge appears to be a very promising method to prevent leading edge insect contamination.

Carmichael, B. H.

1979-01-01

380

A perspective of laminar-flow control. [aircraft energy efficiency program  

NASA Technical Reports Server (NTRS)

A historical review of the development of laminar flow control technology is presented with reference to active laminar boundary-layer control through suction, the use of multiple suction slots, wind-tunnel tests, continuous suction, and spanwise contamination. The ACEE laminar flow control program is outlined noting the development of three-dimensional boundary-layer codes, cruise-noise prediction techniques, airfoil development, and leading-edge region cleaning. Attention is given to glove flight tests and the fabrication and testing of wing box designs.

Braslow, A. L.; Muraca, R. J.

1978-01-01

381

Aircraft energy efficiency laminar flow control glove flight conceptual design study  

NASA Technical Reports Server (NTRS)

A laminar flow control glove applied to the wing of a short to medium range jet transport with aft mounted engines was designed. A slotted aluminum glove concept and a woven stainless steel mesh porous glove concept suction surfaces were studied. The laminar flow control glove and a dummy glove with a modified supercritical airfoil, ducting, modified wing leading and trailing edges, modified flaps, and an LFC trim tab were applied to the wing after slot spacing suction parameters, and compression power were determined. The results show that a laminar flow control glove can be applied to the wing of a jet transport with an appropriate suction system installed.

Wright, A. S.

1979-01-01

382

Control of supersonic wind-tunnel noise by laminarization of nozzle-wall boundary layer  

NASA Technical Reports Server (NTRS)

One of the principal design requirements for a quiet supersonic or hypersonic wind tunnel is to maintain laminar boundary layers on the nozzle walls and thereby reduce disturbance levels in the test flow. The conditions and apparent reasons for laminar boundary layers which have been observed during previous investigations on the walls of several nozzles for exit Mach numbers from 2 to 20 are reviewed. Based on these results, an analysis and an assessment of nozzle design requirements for laminar boundary layers including low Reynolds numbers, high acceleration, suction slots, wall temperature control, wall roughness, and area suction are presented.

Beckwith, I. E.; Harvey, W. D.; Harris, J. E.; Holley, B. B.

1973-01-01

383

Throat stability-by pass systems to increase the stable airflow range of a Mach 2.5 inlet with 60-percent internal contraction  

NASA Technical Reports Server (NTRS)

The results of an experimental investigation to increase the stable airflow range (without unstart) of a supersonic mixed-compression inlet are presented. Various stability bypass entrances were located on the cowl side of the inlet throat. The types of entrance were distributed porous (normal holes), forward-slanted slot, and distributed educated slots. A large stable airflow range was obtained for each entrance type if a constant pressure was maintained in the stability bypass plenum. The distributed porous entrance provided the largest stable airflow range. Inlet unstart angle of attack was unaffected by the entrances.

Mitchell, G. A.; Sanders, B. W.; Shaw, R. J.

1974-01-01

384

Distributed porous throat stability bypass to increase the stable airflow range of a Mach 2.5 inlet with 60 percent internal contraction  

NASA Technical Reports Server (NTRS)

The results of an experimental investigation to increase the stable airflow operating range of a supersonic, mixed-compression inlet with 60-percent internal contraction are presented. Various distributed-porous, throat stability-bypass entrance configurations were tested. In terms of diffuser-exit corrected airflow, a large inlet stable airflow range of about 25 percent was obtained with the optimum configuration if a constant pressure was maintained in the by-pass plenum. The location of the centerbody bleed region had a decided effect on the overall inlet performance. Limited unstart angle-of-attack data are presented.

Shaw, R. J.; Mitchell, G. A.; Sanders, B. W.

1974-01-01

385

The effect of glycine-powder airflow and hand instrumentation on peri-implant soft tissues: a split-mouth pilot study.  

PubMed

Fifteen edentulous patients with overdentures supported by two implants in the mandibular canine regions received periodontal therapy using both hand instrumentation with Teflon curettes and a glycine-based airflow system. Periodontal probing depth (PPD), bleeding on probing (BOP), and bacterial content (BC) within the gingival sulcus were analyzed. A significant effect modification of the glycine airflow with respect to time was found for PPD (P = .01), BOP (P < .001), and BC (P = .004), which were treated as ordered categorical variables. Glycine airflow may be more effective than Teflon curettes for the maintenance of periimplant soft tissues. PMID:23342332

Mussano, Federico; Rovasio, Stefania; Schierano, Gianmario; Baldi, Ileana; Carossa, Stefano

2013-01-01

386

Design and operation of a laminar-flow electrostatic-quadrupole-focused acceleration column  

SciTech Connect

This report deals with the design principles involved in the design of a laminar-flow electrostatic-quadrupole-focused acceleration column. In particular, attention will be paid to making the parameters suitable for incorporation into a DC MEQALAC design.

Maschke, A.W.

1983-06-20

387

Laminar drag reduction in microchannels using ultrahydrophobic surfaces Jia Ou, Blair Perot, and Jonathan P. Rothstein  

E-print Network

Laminar drag reduction in microchannels using ultrahydrophobic surfaces Jia Ou, Blair Perot November 2004) A series of experiments is presented which demonstrate significant drag reduction are obtained using ultrahydrophobic surfaces. No drag reduction is observed for smooth hydrophobic surfaces

Rothstein, Jonathan

388

Fabrication of a graphite/epoxy composite leading edge for laminar flow control  

NASA Technical Reports Server (NTRS)

Lockheed, under NASA contract, has recently completed the first phase of a program to evaluate laminar flow control concepts for transport aircraft. Achievement of laminar flow over a wing surface requires a system of slots, metering holes, ducts and pumps to be used to remove the turbulent air adjacent to the surface. This requirement poses severe restrictions on conventional metallic structure. Graphite/epoxy composite with its unique properties appears to be the material that might solve the very complex structural problems associated with a laminar flow control aircraft. A six-foot span graphite/epoxy test article incorporating provisions for leading edge cleaning, deicing and laminar flow control was designed, fabricated and tested.

Beall, R. T.

1980-01-01

389

Laminar boundary layer in conditions of natural transition to turbulent flow  

NASA Technical Reports Server (NTRS)

Results of experimental study of regularities of a natural transition of a laminar boundary layer to a turbulent layer at low subsonic air flow velocities are presented, analyzed and compared with theory and model experiments.

Polyakov, N. F.

1986-01-01

390

An investigation of the effects of the propeller slipstream of a laminar wing boundary layer  

NASA Technical Reports Server (NTRS)

A research program is in progress to study the effects of the propeller slipstream on natural laminar flow. Flight and wind tunnel measurements of the wing boundary layer have been made using hot-film velocity sensor probes. The results show the boundary layer, at any given point, to alternate between laminar and turbulent states. This cyclic behavior is due to periodic external flow turbulence originating from the viscous wake of the propeller blades. Analytic studies show the cyclic laminar/turbulent boundary layer to result in a significantly lower wing section drag than a fully turbulent boundary layer. The application of natural laminar flow design philosophy yields drag reduction benefits in the slipstream affected regions of the airframe, as well as the unaffected regions.

Howard, R. M.; Miley, S. J.; Holmes, B. J.

1985-01-01

391

A flight test of laminar flow control leading-edge systems  

NASA Technical Reports Server (NTRS)

NASA's program for development of a laminar flow technology base for application to commercial transports has made significant progress since its inception in 1976. Current efforts are focused on development of practical reliable systems for the leading-edge region where the most difficult problems in applying laminar flow exist. Practical solutions to these problems will remove many concerns about the ultimate practicality of laminar flow. To address these issues, two contractors performed studies, conducted development tests, and designed and fabricated fully functional leading-edge test articles for installation on the NASA JetStar aircraft. Systems evaluation and performance testing will be conducted to thoroughly evaluate all system capabilities and characteristics. A simulated airline service flight test program will be performed to obtain the operational sensitivity, maintenance, and reliability data needed to establish that practical solutions exist for the difficult leading-edge area of a future commercial transport employing laminar flow control.

Fischer, M. C.; Wright, A. S., Jr.; Wagner, R. D.

1983-01-01

392

Effects of Lewis number and ignition energy on the determination of laminar flame speed  

E-print Network

, and experimentally by using hydrogen/air mixtures. Emphasis is placed on how to accurately determine the laminar in a confined bomb is found to be one of the most favorable, especially at high pres- sures [3

Ju, Yiguang

393

Observations and implications of natural laminar flow on practical airplane surfaces  

NASA Technical Reports Server (NTRS)

The results of natural laminar flow (NLF) experiments conducted by NASA to determine if modern aircraft structures can benefit from NLF as do sailplanes are presented. Seven aircraft, ranging from a Cessna 210 to a Learjet 28/29, with relatively stiff skins were flown in production configurations with no modifications. Measurements were made of the boundary-layer laminar to turbulent transition locations on various aerodynamic surfaces, the effect of a total loss of laminar flow, the effect of the propeller slipstream on the wing boundary-layer transition and the boundary-layer profiles, the wing section profile drag, the effect of flight through clouds, and insect debris contamination effects. Favorable pressure gradients for NLF were concluded to be feasible up to a transition Reynolds number of 11 million. Laminar flows were observed in propeller slipstreams, and insects were found to cause transition 1/4 of the time.

Holmes, B. J.; Obara, C. J.

1982-01-01

394

Analysis of Low-Speed Stall Aerodynamics of a Swept Wing with Laminar-Flow Glove  

NASA Technical Reports Server (NTRS)

This is the presentation related to the paper of the same name describing Reynolds Averaged Navier Stokes (RANS) computational Fluid Dynamics (CFD) analysis of low speed stall aerodynamics of a swept wing with a laminar flow wing glove.

Bui, Trong

2013-01-01

395

An Approach to the Constrained Design of Natural Laminar Flow Airfoils  

NASA Technical Reports Server (NTRS)

A design method has been developed by which an airfoil with a substantial amount of natural laminar flow can be designed, while maintaining other aerodynamic and geometric constraints. After obtaining the initial airfoil's pressure distribution at the design lift coefficient using an Euler solver coupled with an integral turbulent boundary layer method, the calculations from a laminar boundary layer solver are used by a stability analysis code to obtain estimates of the transition location (using N-Factors) for the starting airfoil. A new design method then calculates a target pressure distribution that will increase the laminar flow toward the desired amount. An airfoil design method is then iteratively used to design an airfoil that possesses that target pressure distribution. The new airfoil's boundary layer stability characteristics are determined, and this iterative process continues until an airfoil is designed that meets the laminar flow requirement and as many of the other constraints as possible.

Green, Bradford E.

1997-01-01

396

Hydrodynamic Suppression of Soot Formation in Laminar Coflowing Jet Diffusion Flames. Appendix C  

NASA Technical Reports Server (NTRS)

Effects of flow (hydrodynamic) properties on limiting conditions for soot-free laminar non-premixed hydrocarbon/air flames (called laminar soot-point conditions) were studied, emphasizing non-buoyant laminar coflowing jet diffusion flames. Effects of air/fuel-stream velocity ratios were of particular interest; therefore, the experiments were carried out at reduced pressures to minimize effects of flow acceleration due to the intrusion of buoyancy. Test conditions included reactant temperatures of 300 K; ambient pressures of 3.7-49 8 kPa; methane-, acetylene-, ethylene-, propane-, and methane-fueled flames burning in coflowing air with fuel-port diameters of 1.7, 3.2, and 6.4 mm, fuel jet Reynolds numbers of 18-121; air coflow velocities of 0-6 m/s; and air/fuel-stream velocity ratios of 0.003-70. Measurements included laminar soot-point flame lengths, laminar soot-point fuel flow rates, and laminar liftoff conditions. The measurements show that laminar soot-point flame lengths and fuel flow rates can be increased, broadening the range of fuel flow rates where the flames remain soot free, by increasing air/fuel-stream velocity ratios. The mechanism of this effect involves the magnitude and direction of flow velocities relative to the flame sheet where increased air/fuel-stream velocity ratios cause progressive reduction of flame residence times in the fuel-rich soot-formation region. The range of soot-free conditions is limited by both liftoff, particularly at low pressures, and the intrusion of effects of buoyancy on effective air/fuel-stream velocity ratios, particularly at high pressures. Effective correlations of laminar soot- and smoke-point flame lengths were also found in terms of a corrected fuel flow rate parameter, based on simplified analysis of laminar jet diffusion flame structure. The results show that laminar smoke-point flame lengths in coflowing air environments are roughly twice as long as soot-free (blue) flames under comparable conditions due to the presence of luminous soot particles under fuel-lean conditions when smoke-point conditions are approached. This is very similar to earlier findings concerning differences between laminar smoke- and sootpoint flame lengths in still environments.

Dai, Z.; Faeth, G. M.; Yuan, Z.-G. (Technical Monitor); Urban, D. L. (Technical Monitor); Yuan, Z.-G. (Technical Monitor)

2000-01-01

397

Laminar burning velocities and flame instabilities of butanol isomers-air mixtures  

SciTech Connect

Laminar burning velocities and flame instabilities of the butanol-air premixed flames and its isomers are investigated using the spherically expanding flame with central ignition at initial temperature of 428 K and initial pressures of 0.10 MPa, 0.25 MPa, 0.50 MPa and 0.75 MPa. Laminar burning velocities and sensitivity factor of n-butanol-air mixtures are computed using a newly developed kinetic mechanism. Unstretched laminar burning velocity, adiabatic temperature, Lewis number, Markstein length, critical flame radius and Peclet number are obtained over a wide range of equivalence ratios. Effect of molecular structure on laminar burning velocity of the isomers of butanol is analyzed from the aspect of C-H bond dissociation energy. Study indicates that although adiabatic flame temperatures of the isomers of butanol are the same, laminar burning velocities give an obvious difference among the isomers of butanol. This indicates that molecular structure has a large influence on laminar burning velocities of the isomers of butanol. Branching (-CH3) will decrease laminar burning velocity. Hydroxyl functional group (-OH) attaching to the terminal carbon atoms gives higher laminar burning velocity compared to that attaching to the inner carbon atoms. Calculated dissociation bond energies show that terminal C-H bonds have larger bond energies than that of inner C-H bonds. n-Butanol, no branching and with hydroxyl functional group (-OH) attaching to the terminal carbon atom, gives the largest laminar burning velocity. tert-Butanol, with highly branching and hydroxyl functional group (-OH) attaching to the inner carbon atom, gives the lowest laminar burning velocity. Laminar burning velocities of iso-butanol and sec-butanol are between those of n-butanol and tert-butanol. The instant of transition to cellularity is experimentally determined for the isomers of butanol and subsequently interpreted on the basis of hydrodynamic and diffusion-thermal instabilities. Little effect on flame instability is observed for the isomers of butanol. Critical flame radii are the same for the isomers of butanol. Peclet number decreases with the increase in equivalence ratio. (author)

Gu, Xiaolei; Huang, Zuohua; Wu, Si; Li, Qianqian [State Key Laboratory of Multiphase Flow in Power Engineering, Xi'an Jiaotong University, Xi'an 710049 (China)

2010-12-15

398

Tackling a Hot Paradox: Laminar Soot Processes-2 (LSP-2)  

NASA Technical Reports Server (NTRS)

The last place you want to be in traffic is behind the bus or truck that is belching large clouds of soot onto your freshly washed car. Besides looking and smelling bad, soot is a health hazard. Particles range from big enough to see to microscopic and can accumulate in the lungs, potentially leading to debilitating or fatal lung diseases. Soot is wasted energy, and therein lies an interesting paradox: Soot forms in a flame's hottest regions where you would expect complete combustion and no waste. Soot enhances the emissions of other pollutants (carbon monoxide and polyaromatic hydrocarbons, etc.) from flames and radiates unwanted heat to combustion chambers (a candle's yellowish glow is soot radiating heat), among other effects. The mechanisms of soot formation are among the most important unresolved problems of combustion science because soot affects contemporary life in so many ways. Although we have used fire for centuries, many fundamental aspects of combustion remain elusive, in part because of limits imposed by the effects of gravity on Earth. Hot or warm air rises quickly and draws in fresh cold air behind it, thus giving flames the classical teardrop shape. Reactions occur in a very small zone, too fast for scientists to observe, in detail, what is happening inside the flame. The Laminar Soot Processes (LSP-2) experiments aboard STS-107 will use the microgravity environment of space to eliminate buoyancy effects and thus slow the reactions inside a flame so they can be more readily studied. 'Laminar' means a simple, smooth fuel jet burning in air, somewhat like a butane lighter. This classical flame approximates combustion in diesel engines, aircraft jet propulsion engines, and furnaces and other devices. LSP-2 will expand on surprising results developed from its first two flights in 1997. The data suggest the existence of a universal relationship, the soot paradigm, that, if proven, will be used to model and control combustion systems on Earth. STS-107 experiments also will help set the stage for extended combustion experiments aboard the International Space Station.

Faeth, Gerard M.; Urban, David L.; Over, Ann (Technical Monitor)

2002-01-01

399

Interactions between soot and CH ? in a laminar boundary layer type diffusion flame in microgravity  

Microsoft Academic Search

A three-dimensional laminar non-buoyant diffusion flame was studied with the objective of improving the understanding of the soot production. The flame originated from a porous ethylene burner discharging into a laminar boundary layer. Soot volume fractions were measured using Laser-Induced Incandescence (LII), and the spontaneous emission from CH? was determined using chemiluminescence. The main parameter varied was the oxidizer flow.

A. Fuentes; G. Legros; A. Claverie; P. Joulain; J.-P. Vantelon; J. L. Torero

2007-01-01

400

Laminar hydathodes in Urticaceae : Survey of tribes and anatomical observations on Pilea pumila and Urtica dioica  

Microsoft Academic Search

Laminar hydathodes are known from only three dicot families. InUrticaceae they are associated with minor vein junctions in all five tribes, as surveyed from cleared leaves of 43 species in 30 genera. Only one species lacked hydathodes. Exclusively adaxial hydathodes were found in 28 genera. In tribeElatostemeae, laminar hydathodes inPilea andPellionia species are abaxial, adaxial, or on both surfaces. Guttation

N. R. Lersten; J. D. Curtis

1991-01-01

401

Field descriptions for a developing laminar tube flow with and without a concentrically located spherical obstacle  

E-print Network

in developing laminar flows at any Reynolds number, and second, no complete pressure fields have been computed using numerical 22 techniques. Blood flow through artificial devices is one example of partic- ulate flows where destruction of the particles...FIELD DESCRIPTIONS FOR A DEVELOPING LAMINAR TUBE FLOW WITH AND WITHOUT A CONCENTRICALLY LOCATED SPHERICAL OBSTACLE A Thesis by CLARK DOUGLAS MIKKELSEN Submitted to the Graduate College of Texas ASM University in partial fulfillment...

Mikkelsen, Clark Douglas

2012-06-07

402

A preliminary design study on an acoustic muffler for the laminar flow transition research apparatus  

NASA Technical Reports Server (NTRS)

An acoustic muffler design of a research tool for studying laminar flow and the mechanisms of transition, the Laminar Flow and Transition Research Apparatus (LFTRA) is investigated. Since the presence of acoustic pressure fluctuations is known to affect transition, low background noise levels in the test section of the LFTRA are mandatory. The difficulties and tradeoffs of various muffler design concepts are discussed and the most promising candidates are emphasized.

Abrahamson, A. L.

1984-01-01

403

Predictable Factors for Dural Tears in Lumbar Burst Fractures with Vertical Laminar Fractures  

PubMed Central

Objective The purpose of the present study was to determine the incidence of dural tears and predictable factors suggesting dural tears in patients who had lumbar burst fractures with vertical laminar fractures. Methods A retrospective review was done on thirty-one patients who underwent operative treatment for lumbar burst fractures with vertical laminar fractures between January 2003 and December 2008. All patients were divided into two groups according to existence of dural tears, which were surgically confirmed; 21 patients with dural tears and 10 patients without dural tears. Clinical and radiographic findings were analyzed for their association with dural tears. Results Among a total of 31 patients, dural tears were detected in 21 (67%) patients. A preoperative neurological deficits and mean separation distances of the edges in laminar fractures were found to be the reliable factors of dural tears (p=0.001 and 0.002, respectively). Decreased ratio of the central canal diameter and interpedicular distance were also the reliable factors suggesting dural tears (p=0.006 and 0.015, respectively). However, dural tears showed no significant association with age, sex, level of injury, absence of a posterior fat pad signal, the angle of retropulsed segment, or site of laminar fracture. Conclusion Our study of lumbar burst fracture combined laminar fracture revealed that dural tears should be ruled out in cases of a preoperative neurological deficits, wide separation of the laminar fracture, severe canal encroachment, and wider interpedicular distance. PMID:21892398

Park, Jin-Kyu; Park, Jin-Woo; Sung, Joo-Kyung

2011-01-01

404

Bone laminarity in the avian forelimb skeleton and its relationship to flight mode: testing functional interpretations.  

PubMed

Wing bone histology in three species of birds was characterized in order to test hypotheses related to the relationship between skeletal microstructure and inferred wing loading during flight. Data on the degree of laminarity (the proportion of circular vascular canals) and the occurrence of secondary osteons were obtained from three species that utilize different primary flight modes: the Double-crested cormorant, a continuous flapper; the Brown pelican, a static soarer; and the Laysan albatross, a dynamic soarer. Laminarity indices were calculated for four quadrants for each of the three main wing elements. Ulnae and carpometacarpi were predicted to exhibit quadrant specific patterns of laminarity due to hypothesized differences in locally applied loads related to the attachment of flight feathers. However, few differences among the quadrants were identified. No significant differences were identified among the three elements, which is notable as different bones are likely experiencing different loading conditions. These results do not support the concept of bone functional adaptation in the primary structure of the wing elements. Significant differences in laminarity were found among the three primary flight modes. The dynamic soaring birds exhibited significantly lower laminarity than the flapping and static soaring birds. These results support the proposed hypothesis that laminarity is an adaptation for resisting torsional loading. This may be explained by overall wing shape: whereas dynamic soaring birds have long slender wings, flappers and static soaring birds have broader wings with a larger wing chord that would necessarily impart a higher torsional moment on the feather-bearing bones. PMID:22241723

Simons, Erin L R; O'connor, Patrick M

2012-03-01

405

Type I Planet Migration in Weakly Magnetized Laminar Disks  

NASA Astrophysics Data System (ADS)

Planet migration plays a crucial role in shaping planetary systems, and has therefore received a lot of attention in recent years in an effort to compare the statistical properties of observed exoplanets with the predictions of planet formation and migration theories. By modifying the propagation properties of the waves induced by the planet in the disk, the presence of a strong magnetic field can dramatically influence planet migration, in some cases reversing its direction. The more realistic case of a weaker magnetic field is less clear, although turbulent MHD simulations by Baruteau et al. (2011) suggest an effect on the corotation torque. Here, we present a study of the corotation torque in 2D laminar disks containing a toroidal magnetic field. We performed MHD simulations of the interaction between the magnetic field and the horseshoe motion of the gas, and found that this results in an additional corotation torque. This additional torque can be strong enough to reverse migration even for a field which pressure is only one percent of the thermal pressure. We speculate that this could lead to long range outward migration in the outer part of protoplanetary disks and may explain the observations by direct imaging of planets at several tens of AU from their star like the 4 planets system HR 8799.

Guilet, Jérôme; Baruteau, Clément; Papaloizou, John C. B.

2014-04-01

406

Cooperative phenomena in laminar fluids: Observation of streamlines  

NASA Astrophysics Data System (ADS)

Complex plasmas are an ideal model system to investigate laminar fluids as they allow to study fluids at the kinetic level. At this level we are able to identify streamlines particle by particle. This gives us the ability to research the behaviour of these streamlines as well as the behaviour of each individual particle of the streamline. We carried out our experiments in a modified GEC-RF-Reference cell. We trapped the particles within two glass rings and forced them to form a circular flow by using several stripe electrodes. In this flow the particles behave like an ideal fluid and form streamlines. By putting an obstacle into the flow we reduce the cross-section. To pass through this constricted cross-section some streamlines have to reconnect. After the obstacle the streamlines split up again. An analysis how streamlines split up and reconnect as result of external pressure on the fluid in our system is presented here. Streamlines also occur if two clouds of particles penetrate each other. We call this ``Lane formation''. Results from our PK-4 experiment are presented here also.

Fink, Martin A.; Kretschmer, M.; Fortov, V.; Höfner, H.; Konopka, U.; Morfill, G. E.; Petrov, O.; Ratynskaia, S.; Usachev, A.; Zobnin, A.

2005-10-01

407

A computational efficient modelling of laminar separation bubbles  

NASA Technical Reports Server (NTRS)

In predicting the aerodynamic characteristics of airfoils operating at low Reynolds numbers, it is often important to account for the effects of laminar (transitional) separation bubbles. Previous approaches to the modelling of this viscous phenomenon range from fast but sometimes unreliable empirical correlations for the length of the bubble and the associated increase in momentum thickness, to more accurate but significantly slower displacement-thickness iteration methods employing inverse boundary-layer formulations in the separated regions. Since the penalty in computational time associated with the more general methods is unacceptable for airfoil design applications, use of an accurate yet computationally efficient model is highly desirable. To this end, a semi-empirical bubble model was developed and incorporated into the Eppler and Somers airfoil design and analysis program. The generality and the efficiency was achieved by successfully approximating the local viscous/inviscid interaction, the transition location, and the turbulent reattachment process within the framework of an integral boundary-layer method. Comparisons of the predicted aerodynamic characteristics with experimental measurements for several airfoils show excellent and consistent agreement for Reynolds numbers from 2,000,000 down to 100,000.

Dini, Paolo; Maughmer, Mark D.

1990-01-01

408

Cooperative phenomena in laminar fluids: Observation of streamlines  

SciTech Connect

Complex plasmas are an ideal model system to investigate laminar fluids as they allow to study fluids at the kinetic level. At this level we are able to identify streamlines particle by particle. This gives us the ability to research the behaviour of these streamlines as well as the behaviour of each individual particle of the streamline.We carried out our experiments in a modified GEC-RF-Reference cell. We trapped the particles within two glass rings and forced them to form a circular flow by using several stripe electrodes. In this flow the particles behave like an ideal fluid and form streamlines. By putting an obstacle into the flow we reduce the cross-section. To pass through this constricted cross-section some streamlines have to reconnect. After the obstacle the streamlines split up again. An analysis how streamlines split up and reconnect as result of external pressure on the fluid in our system is presented here.Streamlines also occur if two clouds of particles penetrate each other. We call this 'Lane formation'. Results from our PK-4 experiment are presented here also.

Fink, Martin A.; Kretschmer, M.; Hoefner, H.; Konopka, U.; Morfill, G.E.; Ratynskaia, S. [Max Planck Institute for extraterrestrial Physics, Giessenbachstrasse, 85741 Garching (Germany); Fortov, V.; Petrov, O.; Usachev, A.; Zobnin, A. [Institute for High Energy Density, Russian Academy of Sciences, ul. Izhorskaya 13/19, 125412 Moscow (Russian Federation)

2005-10-31

409

Numerical simulation of rarefied laminar flow past a circular cylinder  

NASA Astrophysics Data System (ADS)

Numerical simulations have been obtained for two-dimensional laminar flows past a circular cylinder in the transitional regime. Computations are performed using the direct simulation Monte Carlo method for Knudsen numbers of 0.02 and 0.2 and Mach numbers of 0.102 and 0.4. For these conditions, Reynolds number ranges from 0.626 to 24.63 and the flows are steady. Results show that separation occurs in the wake region for the flow with Mach number of 0.4 and Knudsen number of 0.02, but for the other cases flows are attached. The effects of flow speed, rarefaction, domain size and the outflow boundary conditions are investigated. Results show sensitivity to the domain size and the outflow boundary conditions in the low Mach number calculations, but as the speed increases the sensitivity decreases. Although no experimental data are available for direct comparison, the present calculations are found to be in very good agreement with the findings of other researchers.

?elenligil, M. Cevdet

2014-12-01

410

Nusselt numbers in rectangular ducts with laminar viscous dissipation  

SciTech Connect

The need for high thermal performance has stimulated the use of rectangular ducts in a wide variety of compact heat exchangers, mainly in tube-fin and plate-fin exchangers, in order to obtain an enhancement in heat transfer, with the same cross-sectional area of the duct. In this paper, the steady temperature distribution and the Nusselt numbers are analytically determined for a Newtonian incompressible fluid in a rectangular duct, in fully developed laminar flow with viscous dissipation, for any combination of heated and adiabatic sides of the duct, in H1 boundary condition, and neglecting the axial heat conduction in the fluid. The Navier-Stokes and the energy balance equations are solved using the technique of the finite integral transforms. For a duct with four uniformly heated sides (4 version), the temperature distribution and the Nusselt numbers are obtained as a function of the aspect ratio and of the Brinkman number and presented in graphs and tables Finally it is proved that the temperature field in a fully developed T boundary condition can be obtained as a particular case of the H1 problem and that the corresponding Nusselt numbers do not depend on the Brinkman number.

Morini, G.L.; Spiga, M.

1999-11-01

411

Forced and natural convection in laminar-jet diffusion flames  

NASA Astrophysics Data System (ADS)

An experimental investigation was conducted on methane, laminar-jet, diffusion flames with coaxial, forced-air flow to examine flame shapes in zero-gravity and in situations where buoyancy aids (normal-gravity flames) or hinders (inverted-gravity flames) the flow velocities. Fuel nozzles ranged in size from 0.051 to 0.305 cm inside radius, while the coaxial, convergent, air nozzle had a 1.4 cm inside radius at the fuel exit plane. Fuel flows ranged from 1.55 to 10.3 cu cm/sec and air flows from 0 to 597 cu cm/sec. A computer program developed under a previous government contract was used to calculate the characteristic dimensions of normal and zero-gravity flames only. The results include a comparison between the experimental data and the computed axial flame lengths for normal gravity and zero gravity which showed good agreement. Inverted-gravity flame width was correlated with the ratio of fuel nozzle radius to average fuel velocity. Flame extinguishment upon entry into weightlessness was studied, and it was found that relatively low forced-air velocities (approximately 10 cm/sec) are sufficient to sustain methane flame combustion in zero gravity. Flame color is also discussed.

Haggard, J. B., Jr.

1981-06-01

412

Progress Toward Efficient Laminar Flow Analysis and Design  

NASA Technical Reports Server (NTRS)

A multi-fidelity system of computer codes for the analysis and design of vehicles having extensive areas of laminar flow is under development at the NASA Langley Research Center. The overall approach consists of the loose coupling of a flow solver, a transition prediction method and a design module using shell scripts, along with interface modules to prepare the input for each method. This approach allows the user to select the flow solver and transition prediction module, as well as run mode for each code, based on the fidelity most compatible with the problem and available resources. The design module can be any method that designs to a specified target pressure distribution. In addition to the interface modules, two new components have been developed: 1) an efficient, empirical transition prediction module (MATTC) that provides n-factor growth distributions without requiring boundary layer information; and 2) an automated target pressure generation code (ATPG) that develops a target pressure distribution that meets a variety of flow and geometry constraints. The ATPG code also includes empirical estimates of several drag components to allow the optimization of the target pressure distribution. The current system has been developed for the design of subsonic and transonic airfoils and wings, but may be extendable to other speed ranges and components. Several analysis and design examples are included to demonstrate the current capabilities of the system.

Campbell, Richard L.; Campbell, Matthew L.; Streit, Thomas

2011-01-01

413

A topological approach to three-dimensional laminar mixing  

NASA Astrophysics Data System (ADS)

Research into laminar mixing has enjoyed a renaissance in the last decade since the realisation that the Thurston--Nielsen (TN) theory of surface homeomorphisms can assist in designing efficient "topologically chaotic" mixers. However, published results to date have been limited to 2D flows and quasi-3D protocols. Motivated by a simple stretching and folding argument used to derive stretching bounds in 2D flows (what Thurston describes as the iterate-and-guess method for constructing invariant train-tracks), we propose a topological approach to fully 3D fluid mixing. We consider periodic braiding of fluid in two orthogonal directions by inducing a flow with strategically placed ghost rods. The action of this braiding may be encoded by a transition matrix describing how certain area elements are mapped onto each other. The spectral radius of this matrix then furnishes an estimate of large-time asymptotic area growth rate. While this approach to mixing does not sit within the rigorous setting for TN theory, we find nonetheless that the predicted area stretch rates are very sharp for some model flows. Furthermore, we find that certain braids that are topologically trivial in 2D are quite effective in 3D.

Finn, Matthew; Jewell, Nathaniel

2010-11-01

414

Erosion of a granular bed driven by laminar fluid flow  

E-print Network

Motivated by examples of erosive incision of channels in sand, we investigate the motion of individual grains in a granular bed driven by a laminar fluid to give us new insights into the relationship between hydrodynamic stress and surface granular flow. A closed cell of rectangular cross-section is partially filled with glass beads and a constant fluid flux $Q$ flows through the cell. The refractive indices of the fluid and the glass beads are matched and the cell is illuminated with a laser sheet, allowing us to image individual beads. The bed erodes to a rest height $h_r$ which depends on $Q$. The Shields threshold criterion assumes that the non-dimensional ratio $\\theta$ of the viscous stress on the bed to the hydrostatic pressure difference across a grain is sufficient to predict the granular flux. Furthermore, the Shields criterion states that the granular flux is non-zero only for $\\theta >\\theta_c$. We find that the Shields criterion describes the observed relationship $h_r \\propto Q^{1/2}$ when the bed height is offset by approximately half a grain diameter. Introducing this offset in the estimation of $\\theta$ yields a collapse of the measured Einstein number $q^*$ to a power-law function of $\\theta - \\theta_c$ with exponent $1.75 \\pm 0.25$. The dynamics of the bed height relaxation are well described by the power law relationship between the granular flux and the bed stress.

A. E. Lobkovsky; A. V. Orpe; R. Molloy; A. Kudrolli; D. H. Rothman

2008-05-01

415

Drag Measurements in Laminar Flows over Superhydrophobic Porous Membranes  

NASA Astrophysics Data System (ADS)

An anomalous hydrodynamic response has recently been observed in oscillating flows on mesh-like porous superhydrophobic membranes.ootnotetextS. Rajauria, O. Ozsun, J. Lawall, V. Yakhot, and K. L. Ekinci, Phys. Rev. Lett. 107, 174501 (2011) This effect was attributed to a stable Knudsen layer of gas at the solid-liquid interface. In this study, we investigate laminar channel flow over these porous superhydrophobic membranes. We have fabricated surfaces with solid area fraction ?s, which can maintain intimate contact with both air and water reservoirs on either side. Typical structures have linear dimensions of 1.5 mm x 15 mm x 1 ?m and pore area of 10 ?m x 10 ?m. The surfaces are enclosed with precisely machined plastic microchannels, where pressure driven flow of DI water is generated. Pressure drop across the microchannels is measured as a function of flow rate. Slip lengths are inferred from the Poiseuille relation as a function of ?s and compared to that of similar standard superhydrophobic surfaces, which lack intimate contact with an air reservoir.

Ozsun, Ozgur; Yakhot, Victor; Ekinci, Kamil L.

2012-02-01

416

Numerical study of ethylene and acetylene laminar flame speeds  

SciTech Connect

Detailed chemical kinetic computations for ethylene-air and acetylene-air mixtures have been performed to simulate laminar flame speeds. Sensitivity analysis was applied to determine those reactions which strongly influence flame propagation. In ethylene-air mixtures, the C{sub 2}H{sub 3} + O{sub 2} = CH{sub 2}CHO + O reaction was one of the most sensitive reactions in the C{sub 2}H{sub 4}/C{sub 2}H{sub 3} submechanism and therefore this reaction was very important to ethylene flame propagation. This reaction was not considered in previously reported mechanisms used to model ethylene-air flame propagation. In acetylene-air mixtures, the C{sub 2}H{sub 2}+O {yields} Products, HCCO+H=CH{sub 2}(s)+CO, HCCO+O{sub 2}=CO{sub 2}+CO+H, H+C{sub 2}H{sub 2}(+M) = C{sub 2}H{sub 3}(+M) and CH{sub 2}(s)+C{sub 2}H{sub 2} = H{sub 2}CCCH+H were the most sensitive reactions in the C{sub 2}H{sub 2}/HCCO / CH{sub 2}(s) reaction set.

Marinov, N.M.; Pitz, W.J.; Westbrook, C.K.

1995-03-01

417

Dental imaging using laminar optical tomography and micro CT  

NASA Astrophysics Data System (ADS)

Dental lesions located in the pulp are quite difficult to identify based on anatomical contrast, and, hence, to diagnose using traditional imaging methods such as dental CT. However, such lesions could lead to functional and/or molecular optical contrast. Herein, we report on the preliminary investigation of using Laminar Optical Tomography (LOT) to image the pulp and root canals in teeth. LOT is a non-contact, high resolution, molecular and functional mesoscopic optical imaging modality. To investigate the potential of LOT for dental imaging, we injected an optical dye into ex vivo teeth samples and imaged them using LOT and micro-CT simultaneously. A rigid image registration between the LOT and micro-CT reconstruction was obtained, validating the potential of LOT to image molecular optical contrast deep in the teeth with accuracy, non-invasively. We demonstrate that LOT can retrieve the 3D bio-distribution of molecular probes at depths up to 2mm with a resolution of several hundred microns in teeth.

Long, Feixiao; Ozturk, Mehmet S.; Intes, Xavier; Kotha, Shiva

2014-02-01

418

Investigation of Hypersonic Laminar Heating Augmentation in the Stagnation Region  

NASA Technical Reports Server (NTRS)

Laminar stagnation region heating augmentation is investigated in the AEDC Tunnel 9 at Mach 10 by performing high frequency surface pressure and heat transfer measurements on the Orion CEV capsule at zero degree angle-of-attack for unit Reynolds numbers between 0.5 and 15 million per foot. Heating augmentation increases with Reynolds number, but is also model size dependent as it is absent on a 1.25-inch diameter model at Reynolds numbers where it reaches up to 15% on a 7-inch model. Heat transfer space-time correlations on the 7-inch model show that disturbances convect at the boundary layer edge velocity and that the streamwise integral scale increases with distance. Therefore, vorticity amplification due to stretching and piling-up in the stagnation region appears to be responsible for the stagnation point heating augmentation on the larger model. This assumption is reinforced by the f(exp -11/3) dependence of the surface pressure spectrum compared to the f(exp -1) dependence in the free stream. Vorticity amplification does not occur on the 1.25- inch model because the disturbances are too large. Improved free stream fluctuation measurements will be required to determine if significant vorticity is present upstream or mostly generated behind the bow shock.

Marineau, Eric C.; Lewis, Daniel R.; Smith, Michael S.; Lafferty, John F.; White, Molly E.; Amar, Adam J.

2012-01-01

419

Laminar flow around corners triggers the formation of biofilm streamers  

PubMed Central

Bacterial biofilms have an enormous impact on medicine, industry and ecology. These microbial communities are generally considered to adhere to surfaces or interfaces. Nevertheless, suspended filamentous biofilms, or streamers, are frequently observed in natural ecosystems where they play crucial roles by enhancing transport of nutrients and retention of suspended particles. Recent studies in streamside flumes and laboratory flow cells have hypothesized a link with a turbulent flow environment. However, the coupling between the hydrodynamics and complex biofilm structures remains poorly understood. Here, we report the formation of biofilm streamers suspended in the middle plane of curved microchannels under conditions of laminar flow. Experiments with different mutant strains allow us to identify a link between the accumulation of extracellular matrix and the development of these structures. Numerical simulations of the flow in curved channels highlight the presence of a secondary vortical motion in the proximity of the corners, which suggests an underlying hydrodynamic mechanism responsible for the formation of the streamers. Our findings should be relevant to the design of all liquid-carrying systems where biofilms are potentially present and provide new insights on the origins of microbial streamers in natural and industrial environments. PMID:20356880

Rusconi, Roberto; Lecuyer, Sigolene; Guglielmini, Laura; Stone, Howard A.

2010-01-01

420

Inertial manipulation and transfer of microparticles across laminar fluid streams.  

PubMed

A general strategy for controlling particle movement across streams would enable new capabilities in single-cell analysis, solid-phase reaction control, and biophysics research. Transferring cells across streams is difficult to achieve in a well-controlled manner, since it requires precise control of fluid flow along with external force fields or precisely manufactured mechanical structures. Herein a strategy is introduced for particle transfer based on passive inertial lift forces and shifts in the distribution of these forces for channels with shifting aspect ratios. Uniquely, use of the dominant wall-effect lift parallel to the particle rotation direction is explored and utilized to achieve controllable cross-stream motion. In this way, particles are positioned to migrate across laminar streams and enter a new solution without significant disturbance of the interface at rates exceeding 1000 particles per second and sub-millisecond transfer times. The capabilities of rapid inertial solution exchange (RInSE) for preparation of hematological samples and other cellular assays are demonstrated. Lastly, improvements to inline flow cytometry after RInSE of excess fluorescent dye and focusing for downstream analysis are characterized. The described approach is simply applied to manipulating cells and particles and quickly exposing them to or removing them from a reacting solution, with broader applications in control and analysis of low affinity interactions on cells or particles. PMID:22761059

Gossett, Daniel R; Tse, Henry Tat Kwong; Dudani, Jaideep S; Goda, Keisuke; Woods, Travis A; Graves, Steven W; Di Carlo, Dino

2012-09-10

421

Distributed acoustic receptivity in laminar flow control configurations  

NASA Technical Reports Server (NTRS)

A model problem related to distributed receptivity to free-stream acoustic waves in laminar flow control (LFC) configurations is studied, within the Orr-Sommerfield framework, by a suitable extension of the Goldstein-Ruban theory for receptivity due to localized disturbances on the airfoil surface. The results, thus, complement the earlier work on the receptivity produced by local variations in the surface suction and/or surface admittance. In particular, we show that the cumulative effect of the distributed receptivity can be substantially larger than that of a single, isolated suction strip or slot. Furthermore, even if the receptivity is spread out over very large distances, the most effective contributions come from a relatively short region in vicinity of the lower branch of the neutral stability curve. The length scale of this region is intermediate to that of the mean of these two length scales. Finally, it is found that the receptivity is effectively dominated by a narrow band of Fourier components from the wall-suction and admittance distributions, roughly corresponding to a detuning of less than ten percent with respect to the neutral instability wavenumber at the frequency under consideration. The results suggest that the drop-off in receptivity magnitudes away from the resonant wavenumber is nearly independent of the frequency parameter.

Choudhari, Meelan

1992-01-01

422

The ignition of methanol droplets in a laminar convective environment  

SciTech Connect

Numerical simulations of the ignition of methanol droplets in a laminar convective environment are performed using detailed reaction mechanisms and detailed transport models. The flow velocities of the forced convection ranges from 0.01 up to 5 m/s, whereas the ambient gas temperature is varied between 1300 and 1500 K. The ignition delay time of a single droplet is found to decrease with increasing velocity of the convective gas flow. This decrease is attributed to the steepening of the spatial gradients of the profiles of physical variables, such as species mass fractions or temperature. This steepening is originated by a stronger gas flow and leads to a speed-up of the physical transport processes. For the studied flow conditions, an acceleration of the gas flow on the order of the gravitational acceleration does not show a significant influence on the ignition delay time. A downstream movement of the local ignition point with increasing flow velocity is observed. For higher flow velocities, an ignition in the wake of the droplet followed by an upstream flame propagation is found. After ignition, the formation of an envelope flame is detected. The structure of this envelope flame is studied. (author)

Stauch, R.; Maas, U. [Institut fuer Technische Thermodynamik, Universitaet Karlsruhe, Kaiserstrasse 12, D-76128 Karlsruhe (Germany)

2008-04-15

423

Do chronic changes in nasal airflow have any physiological or pathological effect on the nose and paranasal sinuses? A systematic review.  

PubMed

.A reduction in nasal airflow associated with anatomical defects of the nose such as nasal septal deviation has been proposed to cause nasal pathology. . The majority of animal experiments where one nasal passage is surgically closed over several months report only minor changes in the histology of the nasal epithelium and no rhinitis or sinusitis. .Complete abolition of nasal airflow associated with laryngectomy or the treatment of atrophic rhinitis is not associated with the development of rhinitis or sinusitis. . Radiological studies have shown a lack of association between the degree of nasal septal deviation and evidence of rhinosinusitis. .Such studies provide evidence that reduced nasal airflow causes no significant nasal disease. . There is no convincing evidence that a reduction in nasal airflow is a causative factor for rhinitis or sinusitis. PMID:16441795

Boyce, J; Eccles, R

2006-02-01

424

Resonant frequency does not predict high-frequency chest compression settings that maximize airflow or volume.  

PubMed

High-frequency chest compression (HFCC) is a therapy for cystic fibrosis (CF). We hypothesized that the resonant frequency (f(res)), as measured by impulse oscillometry, could be used to determine what HFCC vest settings produce maximal airflow or volume in pediatric CF patients. In 45 subjects, we studied: f(res), HFCC vest frequencies that subjects used (f(used)), and the HFCC vest frequencies that generated the greatest volume (f(vol)) and airflow (f(flow)) changes as measured by pneumotachometer. Median f(used) for 32 subjects was 14 Hz (range, 6-30). The rank order of the three most common f(used) was 15 Hz (28%) and 12 Hz (21%); three frequencies tied for third: 10, 11, and 14 Hz (5% each). Median f(res) for 43 subjects was 20.30 Hz (range, 7.85-33.65). Nineteen subjects underwent vest-tuning to determine f(vol) and f(flow). Median f(vol) was 8 Hz (range, 6-30). The rank order of the three most common f(vol) was: 8 Hz (42%), 6 Hz (32%), and 10 Hz (21%). Median f(flow) was 26 Hz (range, 8-30). The rank order of the three most common f(flow) was: 30 Hz (26%) and 28 Hz (21%); three frequencies tied for third: 8, 14, and 18 Hz (11% each). There was no correlation between f(used) and f(flow) (r(2) ?=?-0.12) or f(vol) (r(2) = 0.031). There was no correlation between f(res) and f(flow) (r(2) ?= 0.19) or f(vol) (r(2) = 0.023). Multivariable analysis showed no independent variables were predictive of f(flow) or f(vol). Vest-tuning may be required to optimize clinical utility of HFCC. Multiple HFCC frequencies may need to be used to incorporate f(flow) and f(vol). PMID:21438176

Luthy, Sarah K; Marinkovic, Aleksandar; Weiner, Daniel J

2011-06-01

425

Prevalence of Airflow Obstruction in U.S. Adults Aged 40-79 Years: NHANES Data 1988-1994 and 2007-2010.  

PubMed

Abstract Background: The study evaluated the change in the prevalence of airflow obstruction in the U.S. population 40-79 years of age from years 1988-1994 to 2007-2010. Methods: Spirometry data from two representative samples of the U.S. population, the National Health and Nutrition Examination Surveys (NHANES) conducted in 1988-1994 and 2007-2010, were used. The American Thoracic Society/European Respiratory Society (ATS/ERS) criteria were used to define airflow obstruction. Results: Based on ATS/ERS criteria, the overall age-adjusted prevalence of airflow obstruction among adults aged 40-79 years decreased from 16.6% to 14.5% (p < 0.05). Significant decreases were observed for the older age category 60-69 years (20.2% vs. 15.4%; p < 0.01), for males (19.0% vs. 15.4%; p < 0.01), and for Mexican American adults (12.7% vs. 8.4%; p < 0.001). The prevalence of moderate and more severe airflow obstruction decreased also (6.4% vs. 4.4%; p < 0.01). Based on ATS/ERS criteria, during 2007-2010, an estimated 18.3 million U.S. adults 40-79 years had airflow obstruction, 5.6 million had moderate or severe airflow obstruction and 1.4 million had severe airflow obstruction. Conclusions: The overall age-adjusted prevalence of airflow obstruction among U.S. adults aged 40-79 years decreased from 1988-1994 to 2007-2010, especially among older adults, Mexican Americans, and males. PMID:25244575

Doney, Brent; Hnizdo, Eva; Dillon, Charles F; Paulose-Ram, Ryne; Tilert, Timothy; Wolz, Michael; Beeckman-Wagner, Lu-Ann

2014-09-22

426

Investigation on the Performance of Fire Detection Systems for Tunnel Applications––Part 2: Full-Scale Experiments Under Longitudinal Airflow Conditions  

Microsoft Academic Search

This paper presents the results of the full-scale experiments conducted in a laboratory tunnel facility under longitudinal\\u000a airflow conditions and in the Carré-Viger Tunnel. The performance of nine fire detection systems representing five types of\\u000a the fire detection technologies for road tunnel applications was investigated using representative tunnel fire scenarios.\\u000a The changes in fire characteristics caused by longitudinal airflow, such

Z. G. Liu; A. H. Kashef; G. D. Lougheed; G. P. Crampton

2011-01-01

427

Aeolian fetch distance and secondary airflow effects: the influence of micro-scale variables on meso-scale foredune development  

Microsoft Academic Search

Unsuccessful attempts to use process-scale models to predict long-term aeolian sediment transport patterns have long been a feature of aeolian research. It has been proposed that one approach to overcome these problems is to identify micro-scale variables that are im- portant at longer timescales. This paper assesses the contribution of two system variables (secondary airflow patterns and fetch distance) to

Kevin Lynch; Derek W. T. Jackson; J. Andrew G. Cooper

2008-01-01

428

Breathing life into dinosaurs: tackling challenges of soft-tissue restoration and nasal airflow in extinct species.  

PubMed

The nasal region plays a key role in sensory, thermal, and respiratory physiology, but exploring its evolution is hampered by a lack of preservation of soft-tissue structures in extinct vertebrates. As a test case, we investigated members of the "bony-headed" ornithischian dinosaur clade Pachycephalosauridae (particularly Stegoceras validum) because of their small body size (which mitigated allometric concerns) and their tendency to preserve nasal soft tissues within their hypermineralized skulls. Hypermineralization directly preserved portions of the olfactory turbinates along with an internal nasal ridge that we regard as potentially an osteological correlate for respiratory conchae. Fossil specimens were CT-scanned, and nasal cavities were segmented and restored. Soft-tissue reconstruction of the nasal capsule was functionally tested in a virtual environment using computational fluid dynamics by running air through multiple models differing in nasal soft-tissue conformation: a bony-bounded model (i.e., skull without soft tissue) and then models with soft tissues added, such as a paranasal septum, a scrolled concha, a branched concha, and a model combining the paranasal septum with a concha. Deviations in fluid flow in comparison to a phylogenetically constrained sample of extant diapsids were used as indicators of missing soft tissue. Models that restored aspects of airflow found in extant diapsids, such as appreciable airflow in the olfactory chamber, were judged as more likely. The model with a branched concha produced airflow patterns closest to those of extant diapsids. These results from both paleontological observation and airflow modeling indicate that S. validum and other pachycephalosaurids could have had both olfactory and respiratory conchae. Although respiratory conchae have been linked to endothermy, such conclusions require caution in that our re-evaluation of the reptilian nasal apparatus indicates that respiratory conchae may be more widespread than originally thought, and other functions, such as selective brain temperature regulation, could be important. PMID:25312371

Bourke, Jason M; Porter, W M Ruger; Ridgely, Ryan C; Lyson, Tyler R; Schachner, Emma R; Bell, Phil R; Witmer, Lawrence M

2014-11-01

429

The effects of airflow modulation and multi-stage defrost on the performance of an air source heat pump  

E-print Network

Modeling System Performance Cycling Losses Frosting and Defrosting Losses . Heat Pump Defrost Controls. Effects of Frost on Airflow Summary of Literature Reviewed . 7 12 16 26 34 41 TEST FACILITY. Psychrometric Rooms Test Heat Pump . . Indoor... Test Section. . Outdoor Test Section. Data Acquisition and Reduction. Experimental Procedure. 44 46 49 51 52 53 IV BASE CASE TEST RESULTS . System Performance Parameters. Frosting Period . Defrost Initiation. Melt Period . . Drain Period...

Payne, William Vance

1992-01-01

430

Large eddy simulation of the pharyngeal airflow associated with obstructive sleep apnea syndrome at pre and post-surgical treatment.  

PubMed

Obstructive Sleep Apnea Syndrome (OSAS) is the most common sleep-disordered breathing medical condition and a potentially life-threatening affliction. Not all the surgical or non-surgical OSAS therapies are successful for each patient, also in part because the primary factors involved in the etiology of this disorder are not completely understood. Thus, there is a need for improving both diagnostic and treatment modalities associated with OSAS. A verified and validated (in terms of mean velocity and pressure fields) Large Eddy Simulation approach is used to characterize the abnormal pharyngeal airflow associated with severe OSAS and its interaction with the airway wall in a subject who underwent surgical treatment. The analysis of the unsteady flow at pre- and post-treatment is used to illustrate the airflow dynamics in the airway associated with OSAS and to reveal as well, the changes in the flow variables after the treatment. At pre-treatment, large airflow velocity and wall shear stress values were found at the obstruction site in all cases. Downstream of obstruction, flow separation generated flow recirculation regions and enhanced the turbulence production in the jet-like shear layers. The interaction between the generated vortical structures and the pharyngeal airway wall induced large fluctuations in the pressure forces acting on the pharyngeal wall. After the surgery, the flow field instabilities vanished and both airway resistance and wall shear stress values were significantly reduced. PMID:21700289

Mihaescu, Mihai; Mylavarapu, Goutham; Gutmark, Ephraim J; Powell, Nelson B

2011-08-11

431

Numerical Simulation of Airway Dimension Effects on Airflow Patterns and Odorant Deposition Patterns in the Rat Nasal Cavity  

PubMed Central

The sense of smell is largely dependent on the airflow and odorant transport in the nasal cavity, which in turn depends on the anatomical structure of the nose. In order to evaluate the effect of airway dimension on rat nasal airflow patterns and odorant deposition patterns, we constructed two 3-dimensional, anatomically accurate models of the left nasal cavity of a Sprague-Dawley rat: one was based on high-resolution MRI images with relatively narrow airways and the other was based on artificially-widening airways of the MRI images by referencing the section images with relatively wide airways. Airflow and odorant transport, in the two models, were determined using the method of computational fluid dynamics with finite volume method. The results demonstrated that an increase of 34 µm in nasal airway dimension significantly decreased the average velocity in the whole nasal cavity by about 10% and in the olfactory region by about 12% and increased the volumetric flow into the olfactory region by about 3%. Odorant deposition was affected to a larger extent, especially in the olfactory region, where the maximum odorant deposition difference reached one order of magnitude. The results suggest that a more accurate nasal cavity model is necessary in order to more precisely study the olfactory function of the nose when using the rat. PMID:24204875

Wei, Zehong; Xu, Zhixiang; Li, Bo; Xu, Fuqiang

2013-01-01

432

Nasal airflow and thoracoabdominal motion in children using infrared thermographic video processing.  

PubMed

The assessment of apnea and asynchronous breathing requires the application of a facemask connected to a pneumotachograph and inductive transducer bands placed around the chest wall. These contact devices may alter the breathing pattern and are difficult to implement, especially in infants and children. This study validates a contactless image-processing system that simultaneously retrieves breath-related thermal variations from nasal, ribcage, and abdomen regions of interest (ROI) from infrared thermographic video recordings of children. Thermographic videos were obtained in 17 supine, spontaneously breathing unsedated children (0.33-13.75 years), including 8 patients with respiratory pathology. Representative thermographic signals were obtained from each ROI on a frame-by-frame basis. Cronbach's Alpha reliability coefficient assessed the correlation between control nasal pressure period, the visually scored respiratory rate and the fundamental period in the frequency domain of thermographic signals. A cross-correlation function calculated the time delay and the phase angle between ribcage and abdomen variability. A Cronbach's Alpha value of 0.976 (0.992-0.944 95% CI) suggests a small-scale measurement error between thermographic and control periods. The ribcage-abdomen time delay in children with respiratory disease (-0.42?±?0.707?sec) significantly differed from healthy children (0.22?±?0.426?sec, P?=?0.0125). This novel system reliably acquired time-aligned nasal airflow and thoracoabdominal motion estimates without relying on attached sensor performance and detected asynchronous breathing in pediatric patients. PMID:22009760

Goldman, Luis J

2012-05-01

433

Plasma morphology and induced airflow characterization of a DBD actuator with serrated electrode  

NASA Astrophysics Data System (ADS)

Plasma morphology and airflow induced by a dielectric barrier discharge (DBD) actuator, whose exposed electrode geometry is designed with a serrated configuration, are investigated in quiescent air and compared with a DBD actuator consisting of electrodes designed with a standard linear strip configuration. ICCD imaging, electrical measurements and three-component laser Doppler velocimetry were carried out to compare various features of these two actuators. With the serrated configuration, ICCD images of the discharge show that streamers are bent, whereas with the linear configuration they are straight. These curved streamers induce a three-dimensional flow topology, which is confirmed by friction line visualization and velocity measurements. Whereas a two-dimensional wall-jet is induced with the linear configuration, a transverse velocity component is measured with the serrated configuration, implying the creation of spanwise-periodic vorticity. Phase-averaged velocity measurements allow the temporal variation of this transverse velocity to be highlighted. On both sides of a tooth, it has qualitatively the same variation as the longitudinal velocity with respect to the negative or positive half-cycles of the high voltage signal. Moreover, with the same electrical operating parameters, the measured longitudinal velocity was higher, particularly at the tips.

Joussot, R.; Leroy, A.; Weber, R.; Rabat, H.; Loyer, S.; Hong, D.

2013-03-01

434

Schlieren imaging in a dielectric barrier discharge actuator for airflow control  

NASA Astrophysics Data System (ADS)

The operation of a surface dielectric barrier discharge actuator for airflow control has been experimentally investigated. The actuator is constituted by an electrode pair separated by a dielectric Teflon sheet. Several ac supply conditions have been utilized. An electrohydrodynamics interaction was induced in still air, and several fluid-dynamic regimes were obtained. Visualization of the plasma boundary layer during the discharge ignition phase and during the steady state regime was obtained by utilizing a Schlieren diagnostic technique. The vortex morphology and propagation velocities at all supply conditions utilized have been evaluated. Velocity profiles perpendicular to the actuator surface, obtained from Pitot tube measurements, and line intensity profiles, determined by means of Schlieren imaging, have been determined for the steady regime operation. The integral along a line perpendicular to the actuator surface of the light intensity of the Schlieren image has been calculated. The profile obtained is in good agreement with the Pitot velocity profile in all the supply conditions investigated. Numerical simulations were also performed. The calculations confirm the relation between the flow velocity distribution in the boundary layer and the gas density distribution, which is the cause of the Schlieren image.

Cristofolini, A.; Neretti, G.; Roveda, F.; Borghi, C. A.

2012-02-01

435

Insight into drop runback on hydrophilic to superhydrophobic surfaces by shearing airflow  

NASA Astrophysics Data System (ADS)

Drop runback has many diverse applications including airfoil icing and fuel cell flooding. In this talk, we use surface science and fluid dynamics principles to explain incipient runback for a drop exposed to shearing airflow. Through experiments with single drops of water and hexadecane (0.5-100 ?l) on PMMA, Teflon, and a superhydrophobic aluminum surface (SHS), wetting parameters such as surface tension, drop shape and contact angle are found to be major controllers of the minimum required air velocity for drop shedding. Exponential functions are proposed that relate air velocity to drop base length and projected area. By normalizing the results, the three water systems can be collapsed to a single curve that also explains results from other researchers, vastly increasing predictive power. SHS are seen to shed drops more easily compared to the other surfaces, with evidence that the drops roll along the surface instead of sliding. Using high speed video, oscillating drop shape and variation of contact angles are also analyzed as they change with air and drop speed.

Milne, Andrew J. B.; Amirfazli, Alidad

2009-11-01

436

Variation in airways resistance when defined over different ranges of airflows.  

PubMed Central

In eight normal subjects airways resistance (Raw) was assessed over six ranges of airflow (about zero flow at both minimum and maximum lung volumes) using an automated whole body plethysmograph. The intervals of flow used were 21s-1 and 11s-1 spanning zero flow, and 11s-1 and 0.51s-1 measured up to and from zero flow. The wider intervals gave less variable results, the coefficients of variation being of the order 11%, 15%, and 22% for the 2, 1, and 0.51s-1 intervals respectively. In all subjects, at minimum volume Raw was some 1.5 times greater when measured over the ranges at end-expiration than at start-expiration; at maximum volume Raw was some 1.3 times greater when measured over the ranges at end-inspiration than at start-expiration. A slight increase in the slopes of the oscilloscope traces used to determine Raw was observed at minimum volume compared with those at maximum volume. In view of the substantial differences reported it is essential that the exact range of flow, and the respiratory phase used, is described when reporting measurements of Raw. Least variability is obtained by estimating slopes over a wide interval of flow, such as 1 or 21s-1. PMID:684679

Lord, P W; Edwards, J M

1978-01-01

437

Investigation on oblique shock wave control by arc discharge plasma in supersonic airflow  

SciTech Connect

Wedge oblique shock wave control by arc discharge plasma in supersonic airflow was investigated theoretically, experimentally, and numerically in this paper. Using thermal choking model, the change in oblique shock wave was deduced, which refer that the start point of shock wave shifts upstream, the shock wave angle decreases, and its intensity weakens. Then the theoretical results were validated experimentally in a Mach 2.2 wind tunnel. On the test conditions of arc discharge power of approx1 kW and arc plasma temperature of approx3000 K, schlieren photography and gas pressure measurements indicated that the start point of shock wave shifted upstream of approx4 mm, the shock wave angle decreased 8.6%, and its intensity weakened 8.8%. The deduced theoretical results match the test results qualitatively, so thermal mechanism and thermal choking model are rational to explain the problem of oblique shock wave control by arc discharge plasma. Finally, numerical simulation was developed. Based on thermal mechanism, the arc discharge plasma was simplified as a thermal source term that added to the Navier-Stokes equations. The simulation results of the change in oblique shock wave were consistent with the test results, so the thermal mechanism indeed dominates the oblique shock wave control process.

Wang Jian; Li Yinghong [Engineering College, Air Force Engineering University, Xi'an 710038 (China); Xing Fei [College of Economics and Management, Northwest University of Politics and Law, Xi'an 710063 (China)

2009-10-01

438

Airflow in a Multiscale Subject-Specific Breathing Human Lung Model  

E-print Network

The airflow in a subject-specific breathing human lung is simulated with a multiscale computational fluid dynamics (CFD) lung model. The three-dimensional (3D) airway geometry beginning from the mouth to about 7 generations of airways is reconstructed from the multi-detector row computed tomography (MDCT) image at the total lung capacity (TLC). Along with the segmented lobe surfaces, we can build an anatomically-consistent one-dimensional (1D) airway tree spanning over more than 20 generations down to the terminal bronchioles, which is specific to the CT resolved airways and lobes (J Biomech 43(11): 2159-2163, 2010). We then register two lung images at TLC and the functional residual capacity (FRC) to specify subject-specific CFD flow boundary conditions and deform the airway surface mesh for a breathing lung simulation (J Comput Phys 244:168-192, 2013). The 1D airway tree bridges the 3D CT-resolved airways and the registration-derived regional ventilation in the lung parenchyma, thus a multiscale model. Larg...

Choi, Jiwoong; Hoffman, Eric A; Tawhai, Merryn H; Lin, Ching-Long

2013-01-01

439

Electrical and mechanical characteristics of surface AC dielectric barrier discharge plasma actuators applied to airflow control  

NASA Astrophysics Data System (ADS)

The present paper is a wide review on AC surface dielectric barrier discharge (DBD) actuators applied to airflow control. Both electrical and mechanical characteristics of surface DBD are presented and discussed. The first half of the present paper gives the last results concerning typical single plate-to-plate surface DBDs supplied by a sine high voltage. The discharge current, the plasma extension and its morphology are firstly analyzed. Then, time-averaged and time-resolved measurements of the produced electrohydrodynamic force and of the resulting electric wind are commented. The second half of the paper concerns a partial list of approaches having demonstrated a significant modification in the discharge behavior and an increasing of its mechanical performances. Typically, single DBDs can produce mean force and electric wind velocity up to 1 mN/W and 7 m/s, respectively. With multi-DBD designs, velocity up to 11 m/s has been measured and force up to 350 mN/m.

Benard, Nicolas; Moreau, Eric

2014-11-01

440

Preliminary Investigation of Certain Laminar-Flow Airfoils for Application at High Speeds and Reynolds Numbers  

NASA Technical Reports Server (NTRS)

In order to extend the useful range of Reynolds numbers of airfoils designed to take advantage of the extensive laminar boundary layers possible in an air stream of low turbulence, tests were made of the NACA 2412-34 and 1412-34 sections in the NACA low-turbulence tunnel. Although the possible extent of the laminar boundary layer on these airfoils is not so great as for specially designed laminar-flow airfoils, it is greater than that for conventional airfoils, and is sufficiently extensive so that at Reynolds numbers above 11,000,000 the laminar region is expected to be limited by the permissible 'Reynolds number run' and not by laminar separation as is the case with conventional airfoils. Drag measurements by the wake-survey method and pressure-distribution measurements were made at several lift coefficients through a range of Reynolds numbers up to 11,400,000. The drag scale-effect curve for the NACA 1412-34 is extrapolated to a Reynolds number of 30,000,000 on the basis of theoretical calculations of the skin friction. Comparable skin-friction calculations were made for the NACA 23012. The results indicate that, for certain applications at moderate values of the Reynolds number, the NACA 1412-34 and 2412-34 airfoils offer some advantages over such conventional airfoils as the NACA 23012. The possibility of maintaining a more extensive laminar boundary layer on these airfoils should result in a small drag reduction, and the absence of pressure peaks allows higher speeds to be reached before the compressibility burble is encountered. At lower Reynold numbers, below about 10,000,000, these airfoils have higher drags than airfoils designed to operate with very extensive laminar boundary layers.

Jacobs, E.N.; Abbott, Ira H.; von Doenhoff, A.E.

1939-01-01

441

Laminar iridium coating produced by pulse current electrodeposition from chloride molten salt  

NASA Astrophysics Data System (ADS)

Due to the unique physical and chemical properties, Iridium (Ir) is one of the most promising oxidation-resistant coatings for refractory materials above 1800 °C in aerospace field. However, the Ir coatings prepared by traditional methods are composed of columnar grains throughout the coating thickness. The columnar structure of the coating is considered to do harm to its oxidation resistance. The laminar Ir coating is expected to have a better high-temperature oxidation resistance than the columnar Ir coating does. The pulse current electrodeposition, with three independent parameters: average current density (Jm), duty cycle (R) and pulse frequency (f), is considered to be a promising method to fabricate layered Ir coating. In this study, laminar Ir coatings were prepared by pulse current electrodeposition in chloride molten salt. The morphology, roughness and texture of the coatings were determined by scanning electron microscope (SEM), profilometer and X-ray diffraction (XRD), respectively. The results showed that the laminar Ir coatings were composed of a nucleation layer with columnar structure and a growth layer with laminar structure. The top surfaces of the laminar Ir coatings consisted of cauliflower-like aggregates containing many fine grains, which were separated by deep grooves. The laminar Ir coating produced at the deposition condition of 20 mA/cm2 (Jm), 10% (R) and 6 Hz (f) was quite smooth (Ra 1.01 ± 0.09 ?m) with extremely high degree of preferred orientation of <1 1 1>, and its laminar structure was well developed with clear boundaries and uniform thickness of sub-layers.

Zhu, Li'an; Bai, Shuxin; Zhang, Hong; Ye, Yicong

2013-10-01

442

The laminar development of direction selectivity in ferret visual cortex.  

PubMed

Sensory experience plays a critical role in the development of cortical circuits. At the time of eye opening, visual cortical neurons in the ferret exhibit orientation selectivity, but lack direction selectivity, which is a feature of mature cortical neurons in this species. Direction selectivity emerges in the days and weeks following eye opening via a process that requires visual experience. However, the circuit mechanisms that underlie the development of direction selectivity remain unclear. Here, we used microelectrodes to examine the laminar chronology of the development of direction selectivity around the time of eye opening to identify the locations within the cortical circuit that are altered during this process. We found that neurons in layers 4 and 2/3 exhibited weak direction selectivity just before natural eye opening. Layer 4 neurons in animals that had opened their eyes but were younger than postnatal day 35 (PND 35) exhibited modestly increased direction selectivity, but layer 2/3 cells remained as weakly tuned as before eye opening. Animals that had opened their eyes and were PND 35 or older exhibited increased direction selectivity in both layers 4 and 2/3. On average, initial increases in direction selectivity in animals younger than PND 35 were explained by increases in responses to the preferred direction, while subsequent increases in direction selectivity in animals PND 35 or older were explained by decreases in responses to the null direction. These results suggest that all cortical layers are influenced by sensory stimulation during early stages of experience-dependent development. PMID:23238731

Clemens, Jared M; Ritter, Neil J; Roy, Arani; Miller, Julie M; Van Hooser, Stephen D

2012-12-12

443

The laminar development of direction selectivity in ferret visual cortex  

PubMed Central

Sensory experience plays a critical role in the development of cortical circuits. At the time of eye opening, visual cortical neurons in the ferret exhibit orientation selectivity, but lack direction selectivity, which is a feature of mature cortical neurons in this species. Direction selectivity emerges in the days and weeks following eye opening via a process that requires visual experience. However, the circuit mechanisms that underlie the development of direction selectivity remain unclear. Here, we used microelectrodes to examine the laminar chronology of the development of direction selectivity around the time of eye opening in order to identify the locations within the cortical circuit that are altered during this process. We found that neurons in layers 4 and 2/3 exhibited weak direction selectivity just prior to natural eye opening. Layer 4 neurons in animals that had opened their eyes but were younger than postnatal day (PND) 35 exhibited modestly increased direction selectivity, but layer 2/3 cells remained as weakly tuned as before eye opening. Animals that had opened their eyes and were PND 35 or older exhibited increased direction selectivity in both layers 4 and 2/3.On average, initial increases in direction selectivity in animals younger than PND 35 were explained by increases in responses to the preferred direction, while subsequent increases in direction selectivity in animals PND35 or older were explained by decreases in responses to the null direction. These results suggest that all cortical layers are influenced by sensory stimulation during early stages of experience-dependent development. PMID:23238731

Clemens, Jared M.; Ritter, Neil J.; Roy, Arani; Miller, Julie M.; Van Hooser, Stephen D.

2012-01-01

444

Characteristics of laminar flow past a sphere in uniform shear  

NASA Astrophysics Data System (ADS)

Numerical simulations are performed to investigate the characteristics of laminar flow past a sphere in uniform shear. The Reynolds numbers considered are Re =300, 425, and 480 based on the inlet center velocity uc and sphere diameter d. The nondimensional shear rate K of inlet uniform shear is varied from 0 to 0.15, where K =??u?d/uc (??u?) and ??u? is the shear rate at inlet. For all Reynolds numbers investigated, the head of the hairpin vortex loop is always located on the high-velocity side in uniform shear. The flow maintains planar symmetry at Re =300. At Re =425 and 480, the temporal variation in the azimuthal angle of the hairpin vortex formation appearing in the uniform inlet flow is greatly reduced in uniform shear, but the flows still keep asymmetry for most inlet shear rates. However, in the cases of K =0.075 and 0.1, at Re =425, the flows become planar symmetric and their characteristics of formation and evolution of the hairpin vortex loops are different from those of asymmetric flows. In most cases, except the instances showing planar symmetry at Re =425, the Strouhal number and time-averaged drag and lift coefficients increase with increasing inlet shear rate. On the other hand, for K =0.075 and 0.1, showing planar symmetry at Re =425, three different vortices are shed in the wake, resulting in three distinct peak frequencies. Finally, a hysteresis phenomenon switching from planar symmetry to asymmetry (or vice versa) depending on the initial condition is observed at Re =425 and 450, implying that small variations in the flow or initial conditions change the flow field at these Reynolds numbers.

Kim, Dongjoo; Choi, Hyungseok; Choi, Haecheon

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