Holographic flow visualization: State-of-the-art overview
Components and system designs of holographic flow visualization techniques are reviewed. Recording materials, lasers, and data processing and display are discussed.
Trolinger, J. D.↗
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Hypersonic Nozzle/Afterbody Experiment: Flow Visualization and Boundary Layer Experiments
This study was conducted to experimentally characterize the flow field created by the interaction of a single-expansion-ramp-nozzle (SERN) flow with a hypersonic external stream Data were obtained from a generic nozzle/afterbody model in the 3.5-Foot Hypersonic Wind Tunnel of the NASA Ames Research Center in a cooperative experimental program involving Ames and the McDonnell Douglas Aerospace. The model design and test planning were performed in close cooperation with members of the Ames computational fluid dynamics (CFD) team for the National Aero-Space Plane (NASP) program. This paper presents experimental results consisting of oil-flow and shadowgraph flow-visualization photographs, afterbody surface-pressure distributions, boundary-layer rake measurements, and Preston-tube skin-friction measurements.
Keener, Earl R.↗
Flow visualization and motion analysis for a series of four sequential brush seals
Applying the Full Flow Field Tracking (FFFT) method, the flow patterns and the accompanying fluid velocities inside a series of brushes were nonintrusively determined and graphically reconstructed. The visualized flow field revealed regions that are characteristically river-jetting, vortical, and crossflow, and exist upstream, downstream, or within the seal. These flows are especially engendered by variations in fiber void that are spatial and temporal and affect changes in seal leakage and stability. The deformation of the upper half of each of the four sequential brushes as a function of upstream pressure and mass flow was determined. The axial pressure variation across the set of four brushes and the mass flow as a function of the pressure drops are also presented.
Braun, M. J.↗
Water-Tunnel Flow Visualization With a Laser
Experimental conditions for effective visualization determined. NASA technical Memorandum describes preliminary experiments in laser-enhanced flow visualization in water tunnel. Aspects of study include required laser power, flow seeding, model preparation, and photographic techniques. Results of study assist potential users in design and construction of similar equipment.
Beckner, Christine↗
Vapor-screen technique for flow visualization in the Langley Unitary Plan Wind Tunnel
The vapor-screen technique for flow visualization, as developed for the Langley Unitary Plan Wind Tunnel, is described with evaluations of light sources and photographic equipment. Test parameters including dew point, pressure, and temperature were varied to determine optimum conditions for obtaining high-quality vapor-screen photographs. The investigation was conducted in the supersonic speed range for Mach numbers from 1.47 to 4.63 at model angles of attack up to 35 deg. Vapor-screen photographs illustrating various flow patterns are presented for several missile and aircraft configurations. Examples of vapor-screen results that have contributed to the understanding of complex flow fields and provided a basis for the development of theoretical codes are presented with reference to other research.
Morris, O. A.↗
Background Oriented Schlieren (BOS) and other Flow Visualization Developments and Applications at GRC
This is a presentation to be given at an internal NASA Advanced Schlieren Working Group Meeting. The presentation will cover the recent developments and applications of flow visualization methods at GRC. The topics being discussed will include the use of Background Oriented Schlieren (BOS) in the study of screech and its associated shock spacing as well as in the investigation of broadband shock noise reduction in the Jet-Surface Interaction Tests. In addition, other flow visualiztion methods will be discussed in an on-going study comparing schlieren, shadowgraph, BOS, and focusing schlieren.
background oriented schlieren↗
Flow visualization efforts and pilot measurements with a laser-Doppler anemometer in backscatter mode
Activities involving the use flow visualization and laser anemometers are reviewed. In particular, turbulent pipe flow measurements and local velocity determination in a 3 X 3 sq meter wind tunnel are discussed. The calibration of laser anemometer systems using a rotating disk is also addressed.
Buetefisch, K. A.↗
The use of liquid crystals for surface flow visualization
The use of shear-sensitive liquid crystals has become an established technique for diagnostic flow visualization. This technique has been demonstrated to illustrate laminar boundary-layer transition, laminar bubbles, shocks, and separation in flight and wind-tunnel environments. Typical results demonstrate the range of flow features which can be illustrated and some of the challenges and pitfalls which must be addressed. A few remaining issues are discussed which should be resolved to develop this technique to full maturity.
Smith, Stephen C.↗
Flow visualization study of the effect of injection hole geometry on an inclined jet in crossflow
A flow visualization was studied by using neutrally buoyant, helium-filled soap bubbles, to determine the effect of injection hole geometry on the trajectory of an air jet in a crossflow and to investigate the mechanisms involved in jet deflection. Experimental variables were the blowing rate, and the injection hole geometry cusp facing upstream (CUS), cusp facing downstream (CDS), round, swirl passage, and oblong. It is indicated that jet deflection is governed by both the pressure drag forces and the entrainment of free-stream fluid into the jet flow. For injection hole geometries with similar cross-sectional areas and similar mass flow rates, the jet configuration with the larger aspect ratio experienced a greater deflection. Entrainment arises from lateral shearing forces on the sides of the jet, which set up a dual vortex motion within the jet and thereby cause some of the main-stream fluid momentum to be swept into the jet flow. This additional momentum forces the jet nearer the surface. Of the jet configurations, the oblong, CDS, and CUS configutations exhibited the largest deflections. The results correlate well with film cooling effectiveness data, which suggests a need to determine the jet exit configuration of optimum aspect ratio to provide maximum film cooling effectiveness.
Simon, F. F.↗
Flow visualization study of the effect of injection hole geometry on an inclined jet in crossflow
A flow visualization was studied by using neutrally buoyant, helium-filled soap bubbles, to determine the effect of injection hole geometry on the trajectory of an air jet in a crossflow and to investigate the mechanisms involved in jet deflection. Experimental variables were the blowing rate, and the injection hole geometry cusp facing upstream (CUS), cusp facing downstream (CDS), round, swirl passage, and oblong. It is indicated that jet deflection is governed by both the pressure drag forces and the entrainment of free-stream fluid into the jet flow. For injection hole geometries with similar cross-sectional areas and similar mass flow rates, the jet configuration with the larger aspect ratio experienced a greater deflection. Entrainment arises from lateral shearing forces on the sides of the jet, which set up a dual vortex motion within the jet and thereby cause some of the main-stream fluid momentum to be swept into the jet flow. This additional momentum forces the jet nearer the surface. Of the jet configurations, the oblong, CDS, and CUS configurations exhibited the largest deflections. The results correlate well with film cooling effectiveness data, which suggests a need to determine the jet exit configuration of optimum aspect ratio to provide maximum film cooling effectiveness.
Simon, Frederick F.↗
Flow visualization of vortices locked by spanwise blowing over wings featuring a unique leading and trailing-edge flap system
Flow visualization studies were conducted to qualitatively determine the effects of active generation and augmentation of vortex flow over wings by blowing a discrete jet in a spanwise direction in the channel formed by extension of upper surface leading- and trailing-edge flaps. Spanwise blowing from a reflection plane over a rectangular wing was found to generate and lock a dual corotating vortex system within the channel and, at sufficient blowing rates, cause the separated flow off the upper end of the leading-edge flap to reattach to the trailing-edge flap. Test parameters included wing angle of attack, jet momentum coefficient, leading- and trailing-edge flap deflection angle, and jet location above the wing surface. Effects due to removal of the leading- and trailing-edge flap were also investigated.
Erickson, G. E.↗
Flow visualization of the wake of a transport aircraft model with lateral-control oscillations
An exploratory flow visualization study conducted in the Langley Vortex Research Facility to investigate the effectiveness of lateral control surface oscillations as a potential method for wake vortex attenuation on a 0.03 scale model of a wide body jet transport aircraft is described. Effects of both asymmetric surface oscillation (control surfaces move as with normal lateral control inputs) and symmetric surface oscillation (control surfaces move in phase) are presented. The asymmetric case simulated a flight maneuver which was previously investigated on the transport aircraft during NASA/FAA flight tests and which resulted in substantial wake vortex attenuation. Effects on the model wake vortex systems were observed by propelling the model through a two dimensional smoke screen perpendicular to the model flight path. Results are presented as photographic time histories of the wake characteristics recorded with high speed still cameras. Effects of oscillation on the wake roll up are described in some detail, and the amount of vortex attenuation observed is discussed in comparative terms. Findings were consistent with flight test results in that only a small amount of rotation was observed in the wake for the asymmetric case. A possible aerodynamic mechanism contributing to this attenuation is suggested.
Jordan, F. L., Jr.↗
Flow Visualization of Aircraft in Flight by Means of Background Oriented Schlieren Using Celestial Objects
The Background Oriented Schlieren using Celestial Objects series of flights was undertaken in the spring of 2016 at National Aeronautics and Space Administration Armstrong Flight Research Center to further develop and improve a flow visualization technique which can be performed from the ground upon flying aircraft. Improved hardware and imaging techniques from previous schlieren tests were investigated. A United States Air Force T-38C and NASA B200 King Air aircraft were imaged eclipsing the sun at ranges varying from 2 to 6 nautical miles, at subsonic and supersonic speeds.
schlieren photography↗
Force and moment, flow-visualization, and boundary-layer tests on a shuttle orbiter model at Mach 6
Force and moment, flow visualization, and boundary layer state tests were conducted using two 0.004 scale shuttle orbiter models. The force and moment tests were conducted for an angle of attack range from 20 to 40 deg and for Reynolds numbers based on reference length from 0.4 million to 3.6 million. Schlieren photographs were obtained for each angle of attack and Reynolds number. The boundary layer state tests, which were conducted using hot film sensors mounted in a separate model, were conducted over the same range of conditions as the force tests. Test results were combined to show that changes in the boundary layer on a typical hypersonic force test model affect measurement of the axial force coefficient and that the state of the local boundary layer is important for interpreting hypersonic aerodynamic test results.
Calloway, R. L.↗
Flow visualization using a computerized data acquisition system
A computer-driven traversing mechanism combined with mass data storage, data reduction programs, and general-purpose graphics programs permits a visualization of complex flows. A unique seven-hole probe is used which permits reasonably accurate measurements of all average flow properties if the local flow angle does not exceed 80 degrees. A description is given of the wake of a lifting canard surface as this wake passes over a wing. The flow includes concentrated and dissipating vortices, large regions of reduced total pressure, and local flow angles up to 60 deg. All these features can be clearly seen and accurately located in the graphical output.
Gallington, R.↗
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.↗
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.↗
Flow visualization techniques in the Airborne Laser Laboratory program
A turret/fairing assembly for laser applications was designed and tested. Wind tunnel testing was conducted using flow visualization techniques. The techniques used have included the methods of tufting, encapsulated liquid crystals, oil flow, sublimation and schlieren and shadowgraph photography. The results were directly applied to the design of fairing shapes for minimum drag and reduced turret buffet. In addition, the results are of primary importance to the study of light propagation paths in the near flow field of the turret cavity. Results indicate that the flow in the vicinity of the turret is an important factor for consideration in the design of suitable turret/fairing or aero-optic assemblies.
Walterick, R. E.↗