Results for “image velocimetry” — Page 4

NASA NTRS1999

Particle-Image Velocimetry in Microgravity Laminar Jet Diffusion Flames

This paper discusses planned velocity measurements in microgravity laminar jet diffusion flames. These measurements will be conducted using Particle-Image Velocimetry (PIV) in the NASA Glenn 2.2-second drop tower. The observations are of fundamental interest and may ultimately lead to improved efficiency and decreased emissions from practical combustors. The velocity measurements will support the evaluation of analytical and numerical combustion models. There is strong motivation for the proposed microgravity flame configuration. Laminar jet flames are fundamental to combustion and their study has contributed to myriad advances in combustion science, including the development of theoretical, computational and diagnostic combustion tools. Nonbuoyant laminar jet flames are pertinent to the turbulent flames of more practical interest via the laminar flamelet concept. The influence of gravity on these flames is deleterious: it complicates theoretical and numerical modeling, introduces hydrodynamic instabilities, decreases length scales and spatial resolution, and limits the variability of residence time. Whereas many normal-gravity laminar jet diffusion flames have been thoroughly examined (including measurements of velocities, temperatures, compositions, sooting behavior and emissive and absorptive properties), measurements in microgravity gas-jet flames have been less complete and, notably, have included only cursory velocity measurements. It is envisioned that our velocity measurements will fill an important gap in the understanding of nonbuoyant laminar jet flames.

Sunderland, P. B.↗

NASA NTRS2004

General-Purpose Stereo Imaging Velocimetry Technique Developed for Space and Industrial Applications

A new three-dimensional, full-field analysis technique has been developed for industrial and space applications. Stereo Imaging Velocimetry (SIV) will provide full-field analysis for three-dimensional flow data from any optically transparent fluid that can be seeded with tracer particles. The goal of SIV is to provide a means to measure three-dimensional fluid velocities quantitatively and qualitatively at many points. SIV is applicable to any optically transparent fluid experiment. Except for the tracer particles, this measurement technique is nonintrusive. Velocity accuracies are on the order of 95 to 99 percent of fullfield. The system components of SIV include camera calibration, centroid determination, overlap decomposition, particle tracking, stereo matching, and three-dimensional velocity analysis. SIV has been used successfully for space shuttle experiments as well as for fluid flow applications for business and industry.

McDowell, Mark↗

NASA NTRSDate not supplied

Lensless Particle Image Velocimetry

Explore the source record for details and available documents.

particle image velocimetry↗

NASA NTRS1999

Stereo Imaging Velocimetry

A system and a method for measuring three-dimensional velocities at a plurality of points in a fluid employing at least two cameras positioned approximately perpendicular to one another. The cameras are calibrated to accurately represent image coordinates in world coordinate system. The two-dimensional views of the cameras are recorded for image processing and centroid coordinate determination. Any overlapping particle clusters are decomposed into constituent centroids. The tracer particles are tracked on a two-dimensional basis and then stereo matched to obtain three-dimensional locations of the particles as a function of time so that velocities can be measured therefrom The stereo imaging velocimetry technique of the present invention provides a full-field. quantitative, three-dimensional map of any optically transparent fluid which is seeded with tracer particles.

McDowell, Mark↗

NASA NTRSDate not supplied

Development and Assessment of a New Particle Image Velocimetry System in the NASA GRC 225 cm2 Wind Tunnel

As part of an ongoing campaign to provide detailed and thorough measurements in a two-dimensional impinging shock-wave/boundary-layer interaction (SWBLI), a custom implementation of the Particle Image Velocimetry (PIV) measurement technique in the NASA Glenn 225 cm2 Wind Tunnel was constructed. The flow seeding apparatus was devised to locally seed the region of interest in the overall flowfield to avoid coating the viewing window with seed material. The ability of the PIV system to provide small particles which faithfully track the underlying gas-phase flowfield was of key importance for the success of this system to make quality measurements in the SWBLI flowfield. In order to optimize and assess the performance of the particle seeding system, PIV measurements were made across a planar oblique shock wave and particle response was analyzed to quantify the particle lag effects due to the finite inertia of the seed droplets. Video recordings from a camera placed in the wind tunnel plenum tank were also used to discern the near-field behavior of the seeded plume and guide the design evolution of the seeding apparatus. The resulting optimized seeding configuration was applied to make PIV measurements in the wind tunnel test section boundary layer to assess the seed particle spatial coverage and concentration. This sample boundary layer dataset provides an analog to the eventual boundary layer measurements to be made in the axisymmetric test section under much more challenged viewing conditions.

PIV↗

NASA NTRSDate not supplied

Development and Assessment of a New Particle Image Velocimetry System in the NASA GRC 225 cm2 Wind Tunnel

As part of an ongoing campaign to provide detailed and thorough measurements in a two-dimensional impinging shock-wave/boundary-layer interaction (SWBLI), a custom implementation of the Particle Image Velocimetry (PIV) measurement technique in the NASA Glenn 225 cm2 Wind Tunnel was constructed. The flow seeding apparatus was devised to locally seed the region of interest in the overall flowfield to avoid coating the viewing window with seed material. The ability of the PIV system to provide small particles which faithfully track the underlying gas-phase flowfield was of key importance for the success of this system to make quality measurements in the SWBLI flowfield. In order to optimize and assess the performance of the particle seeding system, PIV measurements were made across a planar oblique shock wave and particle response was analyzed to quantify the particle lag effects due to the finite inertia of the seed droplets. Video recordings from a camera placed in the wind tunnel plenum tank were also used to discern the near-field behavior of the seeded plume and guide the design evolution of the seeding apparatus. The resulting optimized seeding configuration was applied to make PIV measurements in the wind tunnel test section boundary layer to assess the seed particle spatial coverage and concentration. This sample boundary layer dataset provides an analog to the eventual boundary layer measurements to be made in the axisymmetric test section under much more challenged viewing conditions.

PIV↗

NASA NTRS2003

Field Effects of Buoyancy on a Premixed Turbulent Flame Studied by Particle Image Velocimetry

Typical laboratory flames for the scientific investigation of flame/turbulence interactions are prone to buoyancy effects. Buoyancy acts on these open flame systems and provides upstream feedbacks that control the global flame properties as well as local turbulence/flame interactions. Consequently the flame structures, stabilization limits, and turbulent reaction rates are directly or indirectly coupled with buoyancy. The objective of this study is to characterize the differences between premixed turbulent flames pointing upwards (1g), pointing downwards (-1g), and in microgravity (mg). The configuration is an inverted conical flame stabilized by a small cone-shaped bluff body that we call CLEAN Flames (Cone-Stabilized Lean Flames). We use two laser diagnostics to capture the velocity and scalar fields. Particle image velocimetry (PIV) measures the mean and root mean square velocities and planar imaging by the flame fronts method outlines the flame wrinkle topology. The results were obtained under typical conditions of small domestic heating systems such as water heaters, ovens, and furnaces. Significant differences between the 1g and -1g flames point to the need for including buoyancy contributions in theoretical and numerical calculations. In Earth gravity, there is a complex coupling of buoyancy with the turbulent flow and heat release in the flame. An investigation of buoyancy-free flames in microgravity will provide the key to discern gravity contributions. Data obtained in microgravity flames will provide the benchmark for interpreting and analyzing 1g and -1g flame results.

Cheng, Robert K.↗

NASA NTRS2020

Johns Hopkins University Stereoscopic Particle Image Velocimetry (SPIV) Test Results

Professor J. Katz at the Johns Hopkins University conducted an experimental investigation of the effect of varying the clearance over the tip of a compressor rotor in an embedded stage through a NASA funded award. The activity provided very detailed stereo Particle Image Velocimetry (PIV) measurements of the tip flow field in their optically index-matched facility. The researchers were able to measure and visualize the unsteady velocity and pressure field in the tip gap area for the first time from which they have published more than 10 Journal papers. The dataset has been used widely within NASA for internal program development. The compressor geometry is part of the NASA Low-Speed Axial Compressor (LSAC) compressor stage geometry which is publicly available. All the casing treatment geometries were published by the researchers at JHU. The PIV data has also been published in several ASME papers and presented at recent TurboExpo Conferences. Many research groups at universities and US industry would like access to this data; therefore, we would like to prepare the data package and release it to public. The data package will be announced on data.nasa.gov.

Compressor↗

NASA NTRS1991

Particle image velocimetry for the surface tension driven convection experiment using a particle displacement tracking technique

The Surface Tension Driven Convection Experiment (STDCE) is a Space Transportation System flight experiment to study both transient and steady thermocapillary fluid flows aboard the USML-1 Spacelab mission planned for 1992. One of the components of data collected during the experiment is a video record of the flow field. This qualitative data is then quantified using an all electronic, two-dimensional particle image velocimetry technique called particle displacement tracking (PDT) which uses a simple space domain particle tracking algorithm. The PDT system is successful in producing velocity vector fields from the raw video data. Application of the PDT technique to a sample data set yielded 1606 vectors in 30 seconds of processing time. A bottom viewing optical arrangement is used to image the illuminated plane, which causes keystone distortion in the final recorded image. A coordinate transformation was incorporated into the system software to correct this viewing angle distortion. PDT processing produced 1.8 percent false identifications, due to random particle locations. A highly successful routine for removing the false identifications was also incorporated, reducing the number of false identifications to 0.2 percent.

Wernet, Mark P.↗

NASA NTRS1991

Particle image velocimetry for the Surface Tension Driven Convection Experiment using a particle displacement tracking technique

The Surface Tension Driven Convection Experiment (STDCE) is a Space Transportation System flight experiment to study both transient and steady thermocapillary fluid flows aboard the USML-1 Spacelab mission planned for 1992. One of the components of data collected during the experiment is a video record of the flow field. This qualitative data is then quantified using an all electronic, two-dimensional particle image velocimetry technique called particle displacement tracking (PDT) which uses a simple space domain particle tracking algorithm. The PDT system is successful in producing velocity vector fields from the raw video data. Application of the PDT technique to a sample data set yielded 1606 vectors in 30 seconds of processing time. A bottom viewing optical arrangement is used to image the illuminated plane, which causes keystone distortion in the final recorded image. A coordinate transformation was incorporated into the system software to correct this viewing angle distortion. PDT processing produced 1.8 percent false identifications, due to random particle locations. A highly successful routine for removing the false identifications was also incorporated, reducing the number of false identifications to 0.2 percent.

Wernet, Mark P.↗

NASA NTRS1996

Application of Particle Image Velocimetry to a Study of Flow About a Multi-Element Airfoil

An experiment was performed on the flap tip vortex shed from a half span Fowler flap. This flap was mounted on a 5 foot span NACA 63(2)-215 Mod B airfoil in the 7 by 10 foot wind tunnel at NASA Ames Research Center. Several noise reduction studies were performed with this model, and the addition of the Particle Image Velocimetry (PIV) research discussed here served as a proof case of large scale PIV. The measurement plane investigated here was a cross plane region. This is cross plane relative to the freestream flow direction. The measurement plane was located at a position 18 inches downstream of the flap trailing edge. This served to prove that measurements could also be made in the more difficult cross plane direction rather than in the downstream flow direction. Lastly the PIV data was used as a practical research tool that yielded important results that could not otherwise be obtained. The flow field area measured was 40 cm by 40 cm square, and served to characterize the downstream flow characteristics of the flap tip vortex under three configurations: the baseline configuration which was the flap and the wing only; the baseline with the addition of a 3/4 span slat; and the baseline with a Flap Edge Device which was designed to reduce the noise generated at the flap. All configurations were tested at a freestream velocity of 64.84 m/s. The test resulted in average velocity fields for the three configurations tested. The velocity fields aided in verifying other testing methods on this particular experiment, and also yielded further insight into the characteristics of the flap tip vortex under the three configurations considered. The velocity data was reduced, and we were able to calculate the vorticity of the flow field. From the position of minimum vorticity the location of the center of the vortex was determined. The circulation was also calculated and aided in comparing the effects of the three configurations on the lifting characteristics of the flap.

Walker, Stephen M.↗

NASA NTRS2001

Velocity Measurement in a Dual-Mode Supersonic Combustor using Particle Image Velocimetry

Temporally and spatially-resolved, two-component measurements of velocity in a supersonic hydrogen-air combustor are reported. The combustor had a single unswept ramp fuel injector and operated with an inlet Mach number of 2 and a flow total temperature approaching 1200 K. The experiment simulated the mixing and combustion processes of a dual-mode scramjet operating at a flight Mach number near 5. The velocity measurements were obtained by seeding the fuel with alumina particles and performing Particle Image Velocimetry on the mixing and combustion wake of the ramp injector. To assess the effects of combustion on the fuel air-mixing process, the distribution of time-averaged velocity and relative turbulence intensity was determined for the cases of fuel-air mixing and fuel-air reacting. Relative to the mixing case, the near field core velocity of the reacting fuel jet had a slower streamwise decay. In the far field, downstream of 4 to 6 ramp heights from the ramp base, the heat release of combustion resulted in decreased flow velocity and increased turbulence levels. The reacting measurements were also compared with a computational fluid dynamics solution of the flow field. Numerically predicted velocity magnitudes were higher than that measured and the jet penetration was lower.

Goyne, C. P.↗

NASA NTRS2007

Subscale Ship Airwake Studies Using Novel Vortex Flow Devices with Smoke, Laser-Vapor-Screen and Particle Image Velocimetry

Ships produce vortices and air-wakes while either underway or stationary in a wind. These flow fields can be detrimental to the conduction of air operations in that they can adversely impact the air vehicles and flight crews. There are potential solutions to these problems for both frigates/destroyers and carriers through the use of novel vortex flow or flow control devices. This appendix highlights several devices which may have application and points out that traditional wind-tunnel testing using smoke, laser-vapor screen, and Particle Image Velocimetry can be useful in sorting out the effectiveness of different devices.

Lamar, John E.↗

NASA NTRS2011

The NASA Subsonic Jet Particle Image Velocimetry (PIV) Dataset

Many tasks in fluids engineering require prediction of turbulence of jet flows. The present document documents the single-point statistics of velocity, mean and variance, of cold and hot jet flows. The jet velocities ranged from 0.5 to 1.4 times the ambient speed of sound, and temperatures ranged from unheated to static temperature ratio 2.7. Further, the report assesses the accuracies of the data, e.g., establish uncertainties for the data. This paper covers the following five tasks: (1) Document acquisition and processing procedures used to create the particle image velocimetry (PIV) datasets. (2) Compare PIV data with hotwire and laser Doppler velocimetry (LDV) data published in the open literature. (3) Compare different datasets acquired at the same flow conditions in multiple tests to establish uncertainties. (4) Create a consensus dataset for a range of hot jet flows, including uncertainty bands. (5) Analyze this consensus dataset for self-consistency and compare jet characteristics to those of the open literature. The final objective was fulfilled by using the potential core length and the spread rate of the half-velocity radius to collapse of the mean and turbulent velocity fields over the first 20 jet diameters.

Bridges, James↗

DOE OSTI2021

Time-resolved particle image velocimetry measurements of the turbulent Richtmyer–Meshkov instability

Experiments are presented on the Richtmyer–Meshkov instability (RMI) with a three-dimensional, multi-mode initial perturbation. The experiments use a vertical shock tube, where a stably stratified interface is formed between air and sulphur hexafluoride (SF 6 ) via counterflow. A perturbation is imposed at the interface by vertical oscillation of the gas column, forming Faraday waves. The interface is accelerated by a Mach 1.17 (in air) shock wave, and the development of the mixing region between the gases is investigated using particle image velocimetry. Following shock acceleration, a reflected shock wave from the bottom of the shock tube interacts with the mixing layer a second time (reshock). The experiment is initialized with both high and low amplitude perturbations to examine the effect of the perturbation amplitude on measured quantities. The instability growth exponent (θ) is determined from the kinetic energy field using the width of the mixing layer and the decay of kinetic energy, which are found to be in agreement when the flow is most strongly excited. A growth exponent of θ ≈ 0.5 is found for all cases except the high-amplitude reshocked regime (where θ ≈ 0.33). High-amplitude experiments exhibit the transitional outer Reynolds number (Re ≡ hh˙/ν >10 4 ) required for mixing transition following the incident shock, and both experiments are elevated well above this threshold following reshock. However, neither set of experiments meet the more stringent requirements proposed by Zhou et al. (Phys. Rev.E, vol. 67, issue 5, 2003) which include the time dependent aspect of the RMI, an observation which is also made when examining the spectra.

42 ENGINEERING↗

NASA NTRS2002

Measurement of Meteor Impact Experiments Using Three-Component Particle Image Velocimetry

The study of hypervelocity impacts has been aggressively pursued for more than 30 years at Ames as a way to simulate meteoritic impacts. Development of experimental methods coupled with new perspectives over this time has greatly improved the understanding of the basic physics and phenomenology of the impact process. These fundamental discoveries have led to novel methods for identifying impact craters and features in craters on both Earth and other planetary bodies. Work done at the Ames Vertical Gun Range led to the description of the mechanics of the Chicxualub crater (a.k.a. K-T crater) on the Yucatan Peninsula, widely considered to be the smoking gun impact that brought an end to the dinosaur era. This is the first attempt in the world to apply three-component particle image velocimetry (3-D PIV) to measure the trajectory of the entire ejecta curtain simultaneously with the fluid structure resulting from impact dynamics. The science learned in these experiments will build understanding in the entire impact process by simultaneously measuring both ejecta and atmospheric mechanics.

Heineck, James T.↗

NASA NTRS1991

Particle image velocimetry experiments for the IML-I spaceflight

The first International Microgravity Laboratory (IML-1), scheduled for spaceflight in early 1992 includes a crystal-growth-from-solution experiment which is equipped with an array of optical diagnostics instrumentation which includes transmission and reflection holography, tomography, schlieren, and particle image displacement velocimetry. During the course of preparation for this spaceflight experiment we have performed both experimentation and analysis for each of these diagnostics. In this paper we describe the work performed in the development of holographic particle image displacement velocimetry for microgravity application which will be employed primarily to observe and quantify minute convective currents in the Spacelab environment and also to measure the value of g. Additionally, the experiment offers a unique opportunity to examine physical phenomena which are normally negligible and not observable. A preliminary analysis of the motion of particles in fluid was performed and supporting experiments were carried out. The results of the analysis and the experiments are reported.

Trolinger, J. D.↗

NASA NTRS2004

An Integrated Centroid Finding and Particle Overlap Decomposition Algorithm for Stereo Imaging Velocimetry

An integrated algorithm for decomposing overlapping particle images (multi-particle objects) along with determining each object s constituent particle centroid(s) has been developed using image analysis techniques. The centroid finding algorithm uses a modified eight-direction search method for finding the perimeter of any enclosed object. The centroid is calculated using the intensity-weighted center of mass of the object. The overlap decomposition algorithm further analyzes the object data and breaks it down into its constituent particle centroid(s). This is accomplished with an artificial neural network, feature based technique and provides an efficient way of decomposing overlapping particles. Combining the centroid finding and overlap decomposition routines into a single algorithm allows us to accurately predict the error associated with finding the centroid(s) of particles in our experiments. This algorithm has been tested using real, simulated, and synthetic data and the results are presented and discussed.

McDowell, Mark↗