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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Turbulent jet patterns in accelerating flows

Results of flow visualization experiments, and a semi-empirical model of a single turbulent jet injected perpendicularly to a different density cross flow are presented. The model is based on integral conservation equations, including the pressure terms appropriate to accelerating flow. It uses an entrainment correlation obtained from previous experiments of a jet in a cross stream. The results show trajectories and spreading rates, and are typified by a set of three parameters: momentum ratio, Froude number and density ratio. Agreement between test and calculated results is encouraging, but tend to be poorer with increasing momentum ratio.

Lipshitz, A.↗
NASA NTRS1993

SPOT satellite mapping of Ice Stream B

Numerous features of glaciological significance appear on two adjoining SPOT High Resolution Visible (HRV) images that cover the onset region of ice stream B. Many small-scale features, such as crevasses and drift plumes, have been previously observed in aerial photography. Subtle features, such as long flow traces that have not been mapped previously, are also clear in the satellite imagery. Newly discovered features include ladder-like runners and rungs within certain shear margins, flow traces that are parallel to ice flow, unusual crevasse patterns, and flow traces originating within shear margins. An objective of our work is to contribute to an understanding of the genesis of the features observed in satellite imagery. The genetic possibilities for flow traces, other lineations, bands of transverse crevasses, shear margins, mottles, and lumps and warps are described.

Merry, Carolyn J.↗
NASA NTRS1999

The Cognitive Consequences of Patterns of Information Flow

The flight deck of a moderm commercial airliner is a complex system consisting of two or more crew and a suite of technological devices. When everything goes right, all modem flight decks are easy to use. When things go sour, however, automated flight decks provide opportunities for new kinds of problems. A recent article in Aviation Week cited industry concern over the problem of verifying the safety of complex systems on automated, digital aircraft, stating that the industry must "guard against the kind of incident in which people and the automation seem to mismanage a minor occurrence or non-routine situation into larger trouble." The design of automated flight deck systems that flight crews find easy to use safely is a challenge in part because this design activity requires a theoretical perspective which can simultaneously cover the interactions of people with each other and with technology. In this paper, I will introduce some concepts that can be used to understand the flight deck as a system that is composed of two or more pilots and a complex suite of automated devices. As I will try to show, without a theory, we can repeat what seems to work, but we may not know why it worked or how to make it work in novel circumstances. Theory allows us to rise above the particulars of specific situations and makes the application of the roots of success in one setting applicable to other settings.

Hutchins, Edwin↗
NASA NTRS1999

The Cognitive Consequences of Patterns of Information Flow

The flight deck of a modern commercial airliner is a complex system consisting of two or more crew and a suite of technological devices. The flight deck of the state-of-the-art Boeing 747-400 is shown. When everything goes right, all modern flight decks are easy to use. When things go sour, however, automated flight decks provide opportunities for new kinds of problems. A recent article in Aviation Week cited industry concern over the problem of verifying the safety of complex systems on automated, digital aircraft, stating that the industry must "guard against the kind of incident in which people and the automation seem to mismanage a minor occurrence or non-routine situation into larger trouble." The design of automated flight deck systems that flight crews find easy to use safely is a challenge in part because this design activity requires a theoretical perspective which can simultaneously cover the interactions of people with each other and with technology. In this paper, some concepts that can be used to understand the flight deck as a system that is composed of two or more pilots and a complex suite of automated devices is introduced.

Hutchins, Edwin↗
NASA NTRS2000

RFI and SCRIMP Model Development and Verification

Vacuum-Assisted Resin Transfer Molding (VARTM) processes are becoming promising technologies in the manufacturing of primary composite structures in the aircraft industry as well as infrastructure. A great deal of work still needs to be done on efforts to reduce the costly trial-and-error methods of VARTM processing that are currently in practice today. A computer simulation model of the VARTM process would provide a cost-effective tool in the manufacturing of composites utilizing this technique. Therefore, the objective of this research was to modify an existing three-dimensional, Resin Film Infusion (RFI)/Resin Transfer Molding (RTM) model to include VARTM simulation capabilities and to verify this model with the fabrication of aircraft structural composites. An additional objective was to use the VARTM model as a process analysis tool, where this tool would enable the user to configure the best process for manufacturing quality composites. Experimental verification of the model was performed by processing several flat composite panels. The parameters verified included flow front patterns and infiltration times. The flow front patterns were determined to be qualitatively accurate, while the simulated infiltration times over predicted experimental times by 8 to 10%. Capillary and gravitational forces were incorporated into the existing RFI/RTM model in order to simulate VARTM processing physics more accurately. The theoretical capillary pressure showed the capability to reduce the simulated infiltration times by as great as 6%. The gravity, on the other hand, was found to be negligible for all cases. Finally, the VARTM model was used as a process analysis tool. This enabled the user to determine such important process constraints as the location and type of injection ports and the permeability and location of the high-permeable media. A process for a three-stiffener composite panel was proposed. This configuration evolved from the variation of the process constraints in the modeling of several different composite panels. The configuration was proposed by considering such factors as: infiltration time, the number of vacuum ports, and possible areas of void entrapment.

Loos, Alfred C.↗
NASA NTRS1995

Investigation of wing upper surface flow-field disturbance due to NASA DC-8-72 in-flight inboard thrust-reverser deployment

An investigation of the wing upper surface flow-field disturbance due to in-flight inboard thrust reverser deployment on the NASA DC-8-72, which was conducted cooperatively by NASA Ames, the Federal Aviation Administration (FAA), McDonnell Douglas, and the Aerospace Industry Association (AIA), is outlined and discussed in detail. The purpose of this flight test was to obtain tufted flow visualization data which demonstrates the effect of thrust reverser deployment on the wing upper surface flow field to determine if the disturbed flow regions could be modeled by computational methods. A total of six symmetric thrust reversals of the two inboard engines were performed to monitor tuft and flow cone patterns as well as the character of their movement at the nominal Mach numbers of 0.55, 0.70, and 0.85. The tufts and flow cones were photographed and video-taped to determine the type of flow field that occurs with and without the thrust reversers deployed. In addition, the normal NASA DC-8 onboard Data Acquisition Distribution System (DADS) was used to synchronize the cameras. Results of this flight test will be presented in two parts. First, three distinct flow patterns associated with the above Mach numbers were sketched from the motion videos and discussed in detail. Second, other relevant aircraft parameters, such as aircraft's angular orientation, altitude, Mach number, and vertical descent, are discussed. The flight test participants' comments were recorded on the videos and the interested reader is referred to the video supplement section of this report for that information.

Hamid, Hedayat U.↗
NASA NTRS1993

Analytical modeling and sensor monitoring for optimal processing of advanced textile structural composites by resin transfer molding

A two-dimensional model of the resin transfer molding (RTM) process was developed which can be used to simulate the infiltration of resin into an anisotropic fibrous preform. Frequency dependent electromagnetic sensing (FDEMS) has been developed for in situ monitoring of the RTM process. Flow visualization tests were performed to obtain data which can be used to verify the sensor measurements and the model predictions. Results of the tests showed that FDEMS can accurately detect the position of the resin flow-front during mold filling, and that the model predicted flow-front patterns agreed well with the measured flow-front patterns.

Loos, Alfred C.↗
NASA NTRS1991

Automated pattern eduction from turbulent flow diagnostics

The development of an automated technique for the eduction of 3-D spatial patterns in vector or scalar diagnostics was completed. The method is based on an iterative convolution between a trial pattern and the data field. It was applied to the analysis of low Reynolds number turbulent channel flow and homogeneous shear flow. The results yielded new information on the dominant flow structures in these flows, particularly with respect to the spatial relationships between various forms of organized motion. A particular application of the pattern eduction method, which is tentatively referred to as an 'adaptive wavelet transformation', is proposed with the objective of investigating the way turbulence structure changes with scale. Preliminary results using data from homogeneous turbulent shear flow simulations are presented. At the low Reynolds numbers of the simulations, there is no evidence of scale similarity. The small scales appear to be associated with the edges of the larger scale vortical structures.

Stretch, Derek D.↗
NASA NTRS1972

Effects of leading-edge camber on low-speed characteristics of slender delta wings

Wind-tunnel studies have been conducted to determine the effects of leading-edge camber on the low-speed aerodynamic characteristics of a thin, sharp-edge 74 deg delta wing. The results include force and moment measurements, pressure distributions, and flow visualization patterns determined from oil flow, tuft and water vapor observations. The study indicated that leading-edge camber near the apex is effective in controlling the pitch-up tendency of slender delta wings.

Wentz, W. H., Jr.↗
NASA NTRS1985

Experimental studies on Taylor-Goertler vortices

Taylor-Goertler vortices arise in boundary layer along concave surfaces due to centrifugal effects. These counter-rotating streamwise vortices are one of three known flow instabilities which lead to boundary layer transition. Coupled with Tollmien-Schlichting waves and cross flow vortices, Taylor-Goertler vortices can triggerr early transition to turbulence. The flow field patterns were studied by flow visualization using a sublimating chemical technique and a three component laser velocimeter was used to study the flow field in the test region. Results from these studies are given and briefly discussed.

Goglia, G. L.↗
NASA NTRS1999

The value of assessing pulmonary venous flow velocity for predicting severity of mitral regurgitation: A quantitative assessment integrating left ventricular function

Although alteration in pulmonary venous flow has been reported to relate to mitral regurgitant severity, it is also known to vary with left ventricular (LV) systolic and diastolic dysfunction. There are few data relating pulmonary venous flow to quantitative indexes of mitral regurgitation (MR). The object of this study was to assess quantitatively the accuracy of pulmonary venous flow for predicting MR severity by using transesophageal echocardiographic measurement in patients with variable LV dysfunction. This study consisted of 73 patients undergoing heart surgery with mild to severe MR. Regurgitant orifice area (ROA), regurgitant stroke volume (RSV), and regurgitant fraction (RF) were obtained by quantitative transesophageal echocardiography and proximal isovelocity surface area. Both left and right upper pulmonary venous flow velocities were recorded and their patterns classified by the ratio of systolic to diastolic velocity: normal (>/=1), blunted (<1), and systolic reversal (<0). Twenty-three percent of patients had discordant patterns between the left and right veins. When the most abnormal patterns either in the left or right vein were used for analysis, the ratio of peak systolic to diastolic flow velocity was negatively correlated with ROA (r = -0.74, P <.001), RSV (r = -0.70, P <.001), and RF (r = -0.66, P <.001) calculated by the Doppler thermodilution method; values were r = -0.70, r = -0.67, and r = -0.57, respectively (all P <.001), for indexes calculated by the proximal isovelocity surface area method. The sensitivity, specificity, and predictive values of the reversed pulmonary venous flow pattern for detecting a large ROA (>0.3 cm(2)) were 69%, 98%, and 97%, respectively. The sensitivity, specificity, and predictive values of the normal pulmonary venous flow pattern for detecting a small ROA (<0.3 cm(2)) were 60%, 96%, and 94%, respectively. However, the blunted pattern had low sensitivity (22%), specificity (61%), and predictive values (30%) for detecting ROA of greater than 0.3 cm(2) with significant overlap with the reversed and normal patterns. Among patients with the blunted pattern, the correlation between the systolic to diastolic velocity ratio was worse in those with LV dysfunction (ejection fraction <50%, r = 0.23, P >.05) than in those with normal LV function (r = -0.57, P <.05). Stepwise linear regression analysis showed that the peak systolic to diastolic velocity ratio was independently correlated with RF (P <.001) and effective stroke volume (P <.01), with a multiple correlation coefficient of 0.71 (P <.001). In conclusion, reversed pulmonary venous flow in systole is a highly specific and reliable marker of moderately severe or severe MR with an ROA greater than 0.3 cm(2), whereas the normal pattern accurately predicts mild to moderate MR. Blunted pulmonary venous flow can be seen in all grades of MR with low predictive value for severity of MR, especially in the presence of LV dysfunction. The blunted pulmonary venous flow pattern must therefore be interpreted cautiously in clinical practice as a marker for severity of MR.

Non-NASA Center↗
NASA NTRS1983

An algorithm for using a laser anemometer to determine mean streamline patterns in a turbulent flow

The technique of tracing out a mean flow streamline with a three dimensional laser Doppler anemometer (LDA) is discussed with respect to cumulative, systematic errors that are inherent when the motion of the LDA test point is in the direction of the local measured velocity. Using simple potential flows that have variable curvature and inflection points to simulate an LDA experiment, a streamline tracing algorithm is developed that minimizes these errors. Also, the test point path remains close to the correct streamline even when simulated statistical measurement variations are included.

Orloff, K. L.↗
NASA NTRS1990

Average patterns of precipitation and plasma flow in the plasma sheet flux tubes during steady magnetospheric convection

Average patterns of plasma drifts and auroral precipitation in the nightside auroral zone were constructed during a steady magnetospheric convection (SMC) event on February 19, 1978. By comparing these patterns with the measurements in the midtail plasma sheet made by ISEE-1, and using the corresponding magnetic field model, the following features are inferred: (1) the concentration of the earthward convection in the midnight portion of the plasma sheet (convection jet); (2) the depleted plasma energy content of the flux tubes in the convection jet region; and (3) the Region-1 field-aligned currents generated in the midtail plasma sheet. It is argued that these three elements are mutually consistent features appearing in the process of ionosphere-magnetosphere interaction during SMC periods. These configurational characteristics resemble the corresponding features of substorm expansions (enhanced convection and 'dipolarized' magnetic field within the substorm current wedge) and appear to play the same role in regulating the plasma flow in the flux tubes connected to the plasma sheet.

Sergeev, V. A.↗
NASA NTRS1993

Condition of the Ross Ice Shelf derived from AVHRR imagery

Advanced Very High Resolution Radiometer (AVHRR) satellite imagery is combined with the Ross Ice Shelf Geophysical and Glaciological Survey (RIGGS) data to study recent changes on the Ross Ice Shelf. Flow stripes that appear on the AVHRR imagery agree with significant changes in ice flow that have occurred over the past 1,100 years on the ice shelf sector fed by East Antarctica. A large looping pattern of flow stripes that disagrees with RIGGS flow lines appears west of Crary Ice Rise, on the eastern part of the ice shelf. This looped pattern is interpreted as relict flow stripes related to past activity of a major ice stream of West Antarctica, which occurred about 800 years ago.

Casassa, Gino↗