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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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Application of the wide-field shadowgraph technique to helicopters in forward flight

A test was conducted to examine the feasibility of using the wide-field shadowgraph method for visualizing the wake of a small-scale helicopter rotor in forward flight. A wide range of test conditions were examined, including thrust and forward speed variations. Shadowgraphs from the side and top of the rotor were obtained. The visibility of the tip vortices using the shadowgraph method was documented for advance ratios up to 0.175. It was demonstrated that shadowgraphs of the rotor wake in forward flight can be used to obtain qualitative and quantitative information about wake geometry, wake/body interactions, and blade/vortex interactions. Video cameras were used for the first time to record the shadowgraphs. These provided several advantages compared to still cameras and greatly enhanced the capabilities of the shadowgraph method.

Light, Jeffrey S.↗
NASA NTRS1994

A shadowgraph study of Space Transportation System (STS): The Space Shuttle Launch Vehicle (SSLV)

A shadowgraph study of the space transportation system (STS), the space shuttle launch vehicle, is presented. The shadowgraphs presented in this study were obtained over the past 10 years from wind tunnel tests performed in the NASA Marshall Space Flight Center's 14-Inch Trisonic Wind Tunnel during the space shuttle development program. Shadowgraphs of the STS at various angles-of-attack and roll angles are shown for the Mach range of 0.6 to 4.96. The major flow field phenomena over the mated vehicle configuration are shown in these shadowgraphs. Shadowgraphs are also presented for the orbiter without the lower stack (reentry configuration) and the lower stack without the orbiter. A short study of external tank nose geometry effects on the mated vehicles flow field is presented. These shadowgraphs are used in the aerothermodynamic analysis of the external flow conditions the launch vehicle encounters during the ascent stage of flight.

Springer, A. M.↗
NASA NTRS1994

A shadowgraph study of the National Launch System's 1 1/2 stage vehicle configuration and Heavy Lift Launch Vehicle configuration

A shadowgraph study of the National Launch System's (NLS's) 1 1/2 stage and heavy lift launch vehicle (HLLV) configurations is presented. Shadowgraphs are shown for the range of Mach numbers from Mach 0.6 to 5.0 at various angles-of-attack and roll angles. Since the 1 1/2 stage configuration is generally symmetric, no shadowgraphs of any roll angle are shown for this configuration. The major flow field phenomena over the NLS 1 1/2 stage and HLLV configurations are shown in the shadowgraphs. These shadowgraphs are used in the aerothermodynamic analysis of the external flow conditions the launch vehicle would encounter during the ascent stage of flight. The shadowgraphs presented in this study were obtained from configurations tested in the Marshall Space Flight Center's 14-Inch Trisonic Wind Tunnel during 1992.

Pokora, Darlene C.↗
NASA NTRSDate not supplied

Validation of Shadowgraph Spectral Analysis using an SLS Block 2 Wind-Tunnel Model

A flow quantification method has previously been developed that uses high-speed shadowgraph images to extract frequency content of a transonic flow field around a wind-tunnel model. In this method, a classical spectral analysis is performed on a set of shadowgraph image pixels to identify their intensity fluctuation frequencies. The spatial change of the image intensity is related to the second derivative of the density gradient. Examining the change of the density gradient as a function of time can be used to understand the flow field pressure fluctuations. Pressure measurements collected during a Booster Obsolescence Life Extension Forward Attachment Structure Trade Study Test are used to calibrate the shadowgraph-based measurements. The test was performed at the NASA Ames Research Center Unitary Plan Wind Tunnel 11- by 11-foot test section and investigated aerodynamic environment downstream of various booster forward attachment hardware geometries of the Space Launch System Block 2 Cargo configuration. Time-correlated shadowgraph video and model surface pressure measurements were acquired during the test and served as an ideal opportunity to calibrate and validate the shadowgraph image intensity method.

Shadowgraph↗
NASA NTRSDate not supplied

Validation of Shadowgraph Spectral Analysis using an SLS Block 2 Wind-Tunnel Model

A flow quantification method has previously been developed that uses high-speed shadowgraph images to extract frequency content of a transonic flow field around a wind-tunnel model. In this method, a classical spectral analysis is performed on shadowgraph video pixels to identify their intensity fluctuation frequencies. The spatial change of the image intensity is related to the second derivative of the density gradient. Examining the change of the density gradient as a function of time can be used to understand the flow-field pressure fluctuations. Time-varying pressure measurements collected during a Space Launch System (SLS) unsteady aerodynamic test of an advanced Block 2 booster design are used to calibrate the shadowgraph-based measurements. The test was performed at the NASA Ames Research Center Unitary Plan Wind Tunnel 11- by 11-foot test section and investigated the aerodynamic environment downstream of candidate booster forward attachment hardware geometries of the SLS Block 2 Cargo configuration. Time-correlated shadowgraph video and model surface pressure measurements were acquired during the test and served as an ideal opportunity to calibrate and validate the shadowgraph image intensity method.

Shadowgraph↗
NASA NTRSDate not supplied

Validation of Shadowgraph Spectral Analysis using an SLS Block 2 Wind-Tunnel Model

A flow quantification method has previously been developed that uses high-speed shadowgraph images to extract frequency content of a transonic flow field around a wind-tunnel model. In this method, a classical spectral analysis is performed on shadowgraph video pixels to identify their intensity fluctuation frequencies. The spatial change of the image intensity is related to the second derivative of the density gradient. Examining the change of the density gradient as a function of time can be used to understand the flow-field pressure fluctuations. Time-varying pressure measurements collected during a Space Launch System (SLS) unsteady aerodynamic test of an advanced Block 2 booster design are used to calibrate the shadowgraph-based measurements. The test was performed at the NASA Ames Research Center Unitary Plan Wind Tunnel 11- by 11-foot test section and investigated the aerodynamic environment downstream of candidate booster forward attachment hardware geometries of the SLS Block 2 Cargo configuration. Time-correlated shadowgraph video and model surface pressure measurements were acquired during the test and served as an ideal opportunity to calibrate and validate the shadowgraph image intensity method.

Shadowgraph↗
NASA NTRS1986

Rotor tip vortex geometry measurements using the wide-field shadowgraph technique

Rotor tip vortex geometry data have been acquired using the wide-field shadowgraph technique. Shadowgraphs were taken of the wakes of two model main-rotor systems in hover. These shadowgraphs provided detailed tip vortex trajectories from which axial and radial vortex coordinates were measured. Using these coordinates, prescribed-wake parameters were determined and input into a hover-performance prediction code. The resultant predictions were compared with experimental performance data to help assess the capabilities of this code. Another result of the experimental work was the development of a method to predict the visibility of rotor tip vortices on shadowgraphs. Using this method, the ability of the shadowgraph technique to visualize tip vortices in the rotor wake was quantified.

Norman, T. R.↗
NASA NTRS1993

A shadowgraph study of two proposed Shuttle-C launch vehicle configurations

A shadowgraph study concerning two of the proposed Shuttle-C launch vehicle configurations are presented. These shadowgraphs were obtained from a wind tunnel test performed in Marshall Space Flight Center's 14-in trisonic wind tunnel at various angles-of-attack and roll angles over the Mach range of 0.6 to 4.96. Variations in payload bay length were also evaluated. Major flow field phenomena can easily be seen in the shadowgraphs. Shadowgraphs are a valuable resource. They are used in the analysis of the external flow conditions the launch vehicle encounters through the ascent stage of flight. Subsequent reports will contain shadowgraph studies for other launch vehicle configurations also tested in the Marshall Space Flight Center's 14-in trisonic wind tunnel.

Springer, A. M.↗
NASA NTRS1985

Wide-field shadowgraph flow visualization of tip vortices generated by a helicopter rotor

The vortex trajectory and vortex wake generated by helicopter rotors were visualized using a wide-field shadowgraph technique. Use of a retro-reflective Scotchlite screen made it possible to investigate the flow field generated by full-scale tail rotors. Tip vortex trajectories were visible in shadowgraphs for a range for tip Mach number of 0.38 - 0.60. The effect of the angle of attack was substantial. At an angle of attack greater than 8 degrees, the visibility of the vortex core was significant even at relatively low tip Mach numbers. The theoretical analysis of the visibility was carried out for a rotating blade. This analysis demonstrated that the visibility decreases with increasing dimensionless core radius (ro/c) and increases with increasing tip Mach number. Based on this investigation, it is concluded that the wide-field shadowgraph flow visualization technique should be feasible to study the flow field generated by a large main rotor in a wind tunnel and in an outdoor full-scale test stand. Of note is that the shadowgraph technique could easily be used with other on-going tests such as aerodynamic performance study, noise measurements, velocity measurements with LDV or hot-wire anemometer, local pressure measurement on the rotor surface, etc.

Parthasarathy, S. P.↗
NASA NTRS1985

Fundamental study of flow field generated by rotorcraft blades using wide-field shadowgraph

The vortex trajectory and vortex wake generated by helicopter rotors are visualized using a wide-field shadowgraph technique. Use of a retro-reflective Scotchlite screen makes it possible to investigate the flow field generated by full-scale rotors. Tip vortex trajectories are visible in shadowgraphs for a range of tip Mach number of 0.38 to 0.60. The effect of the angle of attack is substantial. At an angle of attack greater than 8 degrees, the visibility of the vortex core is significant even at relatively low tip Mach numbers. The theoretical analysis of the sensitivity is carried out for a rotating blade. This analysis demonstrates that the sensitivity decreases with increasing dimensionless core radius and increases with increasing tip Mach number. The threshold value of the sensitivity is found to be 0.0015, below which the vortex core is not visible and above which it is visible. The effect of the optical path length is also discussed. Based on this investigation, it is concluded that the application of this wide-field shadowgraph technique to a large wind tunnel test should be feasible. In addition, two simultaneous shadowgraph views would allow three-dimensional reconstruction of vortex trajectories.

Parthasarathy, S. P.↗
NASA NTRS2000

Development of a Large Field of View Shadowgraph System for a 16 Ft. Transonic Wind Tunnel

A large field of view shadowgraph flow visualization system for the Langley 16 ft. Transonic Tunnel (16 ft.TT) has been developed to provide fast, low cost, aerodynamic design concept evaluation capability to support the development of the next generation of commercial and military aircraft and space launch vehicles. Key features of the 16 ft. TT shadowgraph system are: (1) high resolution (1280 X 1024) digital snap shots and sequences; (2) video recording of shadowgraph at 30 frames per second; (3) pan, tilt, & zoom to find and observe flow features; (4) one microsecond flash for freeze frame images; (5) large field of view approximately 12 X 6 ft; and (6) a low maintenance, high signal/noise ratio, retro-reflective screen to allow shadowgraph imaging while test section lights are on.

Talley, Michael A.↗
NASA NTRS2017

Experimental Visualizations of a Generic Launch Vehicle Flow Field: Time-Resolved Shadowgraph and Infrared Imaging

Time-Resolved shadowgraph and infrared (IR) imaging were performed to investigate off-body and on-body flow features of a generic, 'hammer-head' launch vehicle geometry previously tested by Coe and Nute (1962). The measurements discussed here were one part of a large range of wind tunnel test techniques that included steady-state pressure sensitive paint (PSP), dynamic PSP, unsteady surface pressures, and unsteady force measurements. Image data was captured over a Mach number range of 0.6 less than or equal to M less than or equal to 1.2 at a Reynolds number of 3 million per foot. Both shadowgraph and IR imagery were captured in conjunction with unsteady pressures and forces and correlated with IRIG-B timing. High-speed shadowgraph imagery was used to identify wake structure and reattachment behind the payload fairing of the vehicle. Various data processing strategies were employed and ultimately these results correlated well with the location and magnitude of unsteady surface pressure measurements. Two research grade IR cameras were positioned to image boundary layer transition at the vehicle nose and flow reattachment behind the payload fairing. The poor emissivity of the model surface treatment (fast PSP) proved to be challenging for the infrared measurement. Reference image subtraction and contrast limited adaptive histogram equalization (CLAHE) were used to analyze this dataset. Ultimately turbulent boundary layer transition was observed and located forward of the trip dot line at the model sphere-cone junction. Flow reattachment location was identified behind the payload fairing in both steady and unsteady thermal data. As demonstrated in this effort, recent advances in high-speed and thermal imaging technology have modernized classical techniques providing a new viewpoint for the modern researcher

Shadowgraph↗
NASA NTRS1981

Laser shadowgraph and schlieren studies of gravity-related flow during solidification

Shadowgraph and schlieren techniques were used to observe gravity-related flow arising during solidification. The purpose of these studies was to elucidate the results of previous low gravity solidification experiments. Shadowgraph and schlieren techniques were selected as most suitable for operation in the anticipated experimental environment. A laser shadowgraph/schlieren system was built and flown on KC-135 low gravity simulation flights. A solution of ammonium chloride and water was cooled during the experiment, causing solidification. Growth plumes in the solution were observed and photographed using shadowgraph and schlieren techniques. Results are presented and related to previous work.

Owen, R. B.↗
NASA NTRS1984

Experimental investigation of shock-cell noise reduction for single-stream nozzles in simulated flight, comprehensive data report. Volume 3: Shadowgraph photos and facility description

A total of 142 shadowgraph photographs were taken on 43 different plumes that were distributed over the six nozzle configurations using the 9.5 inch diameter collimated light beam of the shadowgraph setup. Aerodynamic flow conditions of the shadowgraph test points, the location and identification of each of the photographs, and copies of the pictures are presented.

Yamamoto, K.↗
NASA NTRS1989

Application of the wide-field shadowgraph technique to rotor wake visualization

The wide field shadowgraph technique is reviewed along with its application to the visualization of rotor wakes. In particular, current experimental methods and data reduction requirements are discussed. Sample shadowgraphs are presented. These include shadowgraphs of model-scale helicopter main rotors and tilt rotors, and full scale tail rotors, both in hover and in forward flight.

Norman, Thomas R.↗
NASA NTRS1993

Application of the shadowgraph flow visualization technique to a full-scale helicopter rotor in hover and forward flight

The wide-field shadowgraph flow visualization technique was used for the first time with a full-scale helicopter rotor. This was accomplished during testing of a Sikorsky S-76 main rotor in the NASA Ames National Full-Scale Aerodynamics Complex (NFAC) 80- by 120-Foot Wind Tunnel. Hover, low-speed forward flight, and descent operating conditions were studied. Preliminary results are very promising with rotor wake tip vortices visible up to an advance ratio of 0.25. In addition, many details of the rotor wake were visible, including tip vortex roll-up, inboard wake vorticity, and flow unsteadiness due to test section recirculation effects in hover. Shadowgraphs of blade/vortex interactions were also acquired. Simultaneous top and side view shadowgraphs of the rotor wake were acquired by a newly developed synchronized digital imaging system. The imaging system proved to be a highly successful tool which made real-time examination of selected regions of the rotor wake possible.

Swanson, Alexandra A.↗
NASA NTRS1975

Shadowgraphs of air flow over prospective space shuttle configurations at Mach numbers from 0.8 to 1.4

Shadowgraphs of five space shuttle launch configurations are presented. The model was a 4 percent-scale space shuttle vehicle, tested in the 11- by 11-foot Transonic Wind Tunnel at Ames Research Center. The Mach number was varied from 0.8 to 1.4 with three angles of sideslip (0 deg, 5 deg and -5 deg) that were used in conjunction with three angles of attack (4 deg, -4 deg, and 0 deg). The model configurations included both series-burn and parallel-burn configurations, two canopy configurations, two positions of the orbiter nose relative to the HO tank nose, and two HO tank nose-cones angles (15 deg and 20 deg). The data consist entirely of shadowgraph photographs.

Dods, J. B., Jr.↗
NASA NTRS1984

Experimental investigation of shock-cell noise reduction for dual-stream nozzles in simulated flight comprehensive data report. Volume 2: Laser velocimeter data, static pressures and shadowgraph photos

Parameters which contribute to supersonic jet shock noise were investigated for the purpose of determining means to reduce such noise generation to acceptable levels. Six dual-stream test nozzles with varying flow passage and plug closure designs were evaluated under simulated flight conditions in an anechoic chamber. All nozzles had combined convergent-divergent or convergent flow passages. Mean velocity and turbulence velocity measurements of 25 selected flow conditions were performed employing a laser Doppler velocimeter. Static pressure measurements were made to define the actual convergence-divergence condition. Test point definition, tabulation of aerodynamic test conditions, velocity histograms, and shadowgraph photographs are presented. Flow visualization through shadowgraph photography can contribute to the development of an analytical prediction model for shock noise from coannular plug nozzles.

Yamamoto, K.↗