The non-intrusive plasma diagnostics program incorporates various laser and other optical methods to measure the concentration, velocity, and temperatures of the different atomic, molecular and ionic species in test facilities that simulate atmospheric entry flows. The data collected in these measurements is used to validate arc jet flow codes that can be used in combination with shock layer codes to understand the heat transfer to the thermal protection materials. Absorption methods are used to estimate the atomic copper concentration in the free stream flow. Emission from the free stream and shock layer is used to identify the radiating species and also their rotational, vibrational and electronic temperatures. Analysis of the shock layer emission resulted in the temperature mapping across the entire shock layer. Laser excited fluorescence measurements are used to determine velocity and temperatures in the free stream as well as shock layer. This paper describes the current status and future development of optical diagnostics for the arc jet facility.

Over the past three years several Particle Image Velocimetry measurements have been made. In each case a different aspect of the technique has been explored. The object of the experiments has been to develop a new set of optical tools. They have been designed to provide both qualitative visualizations and quantitative diagnostic flow field data in high speed flows. One objective of the research has been to image sub-micron particles to visualize the instantaneous behavior of the flow field. The work has also been directed towards test operations which require rapid data acquisition such as transient blowdown or facilities with high running costs. The development period has also provided an optical diagnostic suitable for making measurements in unsteady flow regions. Each measurement made during this development period has been directed toward addressing different aspects of the technique and its application as a flow-field diagnostic.

Automation of interferogram analysis is very important for successful application of all interferometric measurement techniques. In high-speed aerodynamics or experimental mechanics, complex noise-ridden fringe patterns frequently arise due to prevailing adverse environments. In conventional practice, only local information has been heavily utilized to reduce background noise or to correct phase information. Under these circumstances, the currently available techniques, that is, fringe tracking, phase-shifting, Fourier transform, and regression methods, confront difficulties in phase unwrapping and thus need substantial interactive manual operations. The developed rule-based expert system utilizes both global/regional and local information, and makes use of expert knowledge. It can thus provide a potential for more comprehensive automation in noise reduction and phase unwrapping. The developed expert system adopts a hybrid mechanism in a single package, that is, the low-level and high-level processings to produce an optimal solution in fringe analysis. The system can be coupled with any current interferometric reduction techniques, being based on the analysis of isophase contour lines.

An orthogonal axes holographic flow measurement system was developed and applied to support fundamental aero-optics (A/O) testing of free shear layer flows. The two optical axes are mutually orthogonal to the mean flow vector of the flow facility. The horizontal path which was normal to the shear layer was used to observe aero-optics effects. The vertical path which was parallel to the shear layer provided visualization of the flow structure. Focal plane imaging was also obtained from the A/O path to measure aberrations. A pulsed-laser light source provided instantaneous images for both orthogonal paths, including the focal plane image. This allowed the optical distortions normal to the shear layer to be correlated directly with specific flow structures and the variance from diffraction limited performance at the focal plane. This paper describes the design features of the holographic optical system and presents some of the preliminary results to demonstrate performance.

This paper describes an experiment characterizing the statistical properties of laboratory generated turbulence using a shearing interferometer based wavefront sensor. The statistics of the turbulence have been characterized by taking many measurements of optical wavefronts that have propagated through the turbulence. The wavefront sensor is capable of both high time and spatial resolution. The wavefront sensor measures the wavefront phase over a circular area corresponding to the size of the propagated laser beam. Nearly 256 samples of the wavefront phase in both the x- and y-directions are sampled per measurement. From these optical phase measurements, a phase structure function was calculated. Laboratory generated turbulence that produces locally homogeneous and isotropic disturbances has been developed for the purpose of studying current and future adaptive optics and image enhancement techniques.

A flow visualization technique for determining the distribution of hydrogen fuel injected into a high speed pulse-type flow has been developed and successfully demonstrated. This work was carried out in a shock tunnel located at General Applied Science Laboratories. The technique requires seeding the H₂ with sub-micron diameter silicon dioxide particles small enough to assure tagging of the flow field stream lines, even at hypervelocity conditions. A thin laser sheet sliced the test section perpendicularly and, with the use of a free-running black-and- white CCD camera, the Mie scattering off the silica was imaged and recorded. The intensity of the image is directly proportional to the number of scatters which traverse the sampling volume at each planar location.

A loss of beam intensity occurs when a laser beam is propagated through shear layers with optical index fluctuations. A new model which uses Fraunhofer diffraction around a sinusoidal phase grating predicts the loss of intensity accurately. The size of coherent structures within the shear layers determines the spacing and the width of the grating. Numerical results agree well with previous experimental results.

Abstract not available.

In support of ongoing investigations into turbulence generated aero-optic effects, Teledyne Brown Engineering (TBE) has conducted a series of laboratory based experiments on high velocity turbulent mixing/shear layers. The cornerstone of this effort was the TBE designed and fabricated Dual Injection Nozzle Aero-Optic Simulator for Endoatmospheric Research (DINASER). The DINASER was used to generate flow conditions that simulate the aero-optic effects encountered in flight. The goal of the investigation was to collect data that could be used to validate computational fluid dynamic (CFD) codes, evaluate turbulence models, and anchor aero-optic propagation codes, all of which are essential components in flight simulations. From previous experiments and analysis, the unknown quantities necessary to validate the turbulence models and CFD code have been separated from the essential optical quantities. This investigation has primarily focused on the quantification of the optical parameters, measured along the line-of-sight.

Optical refraction in high enthalpy hypersonic flow fields can adversely affect infrared imaging of targets by an optical sensor looking through the flow field from an interceptor. In perhaps one of the most complex aero-optical wind tunnel tests ever attempted, measurements of image blur, Strehl ratios, jitter, and boresight error were made on sensor image data for cases of optical propagation of a collimated beam through the hypersonic flow field over an interceptor forebody in a wind tunnel. Determination of the dependence of the aero-optical effects on coolant gas flow rates for both the forebody and the window was sought. Holographic and other types of optical measurements were made in addition to measurements on images. Analysis of the data required various types of processing in order to obtain the desired information in the presence of equipment vibration, optical system aberrations, and nonlinear focal-plane array response.

This paper discusses the use of time series of the jitter angle of multiple, small-aperture probe beams as they emerge from a turbulent, optically-active flow field to quantify the time-varying optical path difference (OPD). Techniques to reconstruct a complete time series of instantaneous realizations of the OPD are first applied to a numerically-generated flow field and then to an experimental flow field. The flow field studied was that for the transitionally- turbulent region of a heated, two-dimensional jet. From these OPD histories spatial and temporal frequencies characterizing the OPD's are extracted. The relevance of these results to adaptive-optic devices is discussed.

Analysis of data from direct numerical simulation of turbulent shear flows has shown the importance of large-scale, coherent turbulent structure on optical propagation. A basic approach is taken that incorporates both an experimental and a computational effort to develop a fundamental understanding of fluid-optical interactions. A flow generator and diagnostic instrumentation have been designed and are being built to measure the effect that a `simple' canonical turbulent flow has on a transmitted beam. This `simple' flow retains the essence of actual cases of interest, determining the effect of turbulent flow on optical transmission, and yet is tractable. The diagnostics include standard sensors to characterize the flow and optical diagnostics, including tomography, to characterize both the flow and the effect of the flow on beam propagation. A new dynamical system model for passive-scalar transport in a turbulent flow is also being developed to guide the experimental effort and to provide insight on the fluid-optical interactions.

The use of lasers aboard aircraft is affected by the perturbed airflow in its vicinity. Therefore, an ability to predict the structure of aircraft-induced turbulence would be useful in system and performance analysis. PSR performed temperature and velocity fluctuation measurements in the wakes of an NRA-3B and a B-1B at trail distances of 50 to 5500 m, at two Mach numbers (0.5 and 0.75) and at two altitudes (0.9 and 6 km). Preliminary analysis of the data suggested significant differences with the predictions of the computational fluid dynamics code (CFD) WAKE developed for this application by ARAP for U.S. Air Force. These differences impact laser propagation. The principal difference between the data and the CFD predictions is that the temperature fluctuations which determine C²_N are not isotropic and exhibit spectra and correlation scales which differ greatly from those of velocity. This paper reports the development of a hypothesis concerning the source of this temperature structure in aircraft wakes. Modifications to CFD models are suggested.

This paper describes recent aero-optical measurements in the LENS facility, to evaluate the turbulent flow field characteristics of model configurations in hypervelocity airflow. The AOEC instrumentation suited which utilizes visible and infrared light sources, a wide-band optical bus and refractive and radiative sensors is described. Validation studies with simple optical aperture configurations in high enthalpy flow are discussed. The aero-optical instrumentation used in these studies are described.

The effect of a turbulent, free shear layer is to introduce a random phase variation on a light beam propagating through that layer. It an incoming parallel beam is brought to focus after propagating through the layer, then the effect of this added random phase variation is to scatter energy out of a diffraction limited focused spot and form a halo around the spot. In an imaging system, this could degrade image quality and reduce contrast due to scattering of energy over a large area. The rapid growth of a free shear layer results in a phase screen whose characteristics rapidly change with distance in the flow direction, therefore part of the beam may propagate through a benign region of the flow field, while that part of the beam located further downstream may be severely aberrated. The specific flow condition chosen is one in which the flow separates from a cylindrical turret with a large optical aperture. The spatially varying characteristics of a free shear layer are explicitly accounted for by constructing a spatially varying phase screen, in which the aerodynamic characteristics are based on turbulence measurements made on large scale wind tunnel models, and on flight measurements made on a large aircraft. The resultance Strehl ratios and beam profiles for typical flight conditions are presented.

This paper describes an improvement of a two color pyrometer which provides for near simultaneous multi-point measurements, reduced dependence on electronic circuits, and a greatly enhanced data display system. Important reasons for our development of this system include the need to make simultaneous measurements at widely separated points and the measurement of both surface temperature and emissivity. Finally, the data measured by this system is stored on magnetic media and can be correlated with other measurements on the system under study.

Optical measurement techniques are extremely useful in fluid mechanics because of their non- invasive nature. However, it is often difficult to separate measurement effects due to pressure, temperature and density in real flows. Using a variation of a Shack-Hartmann wavefront sensor, we have made wavefront measurements that have extremely large dynamic range coupled with excellent sensitivity at high temporal and spatial resolution. These wavefront variations can be directly related to density perturbations in the fluid. We have examined several classes of flow including volumetrically heated gas, grid turbulence and droplet evaporation.

High temperature water vapor detection in hypersonic exhaust has been the subject of ongoing research in a collaboration between MetroLaser and Vanderbilt University's Department of Mechanical Engineering. In this paper we examine some of the temperature sensitivity issues surrounding water vapor diagnostics based on two-photon fluorescence measurements. We present work which shows a large temperature sensitivity for the two-photon excited fluorescence features for H₂O in a hydrogen and air flat flame burner. The spectra are modeled for various temperatures, results are experimentally verified, and recommendations are made.

A preliminary study has been made into the temporal and spectral characteristics of internally illuminated liquid drops using the Fiber Drop Analyzer (FDA) with the objective of using this instrument for the diagnosis of disease in synovial fluid based on measurements of viscosity, absorbance and other parameters. Two approaches to the measurement of viscosity are identified and described. This study describes for the first time the operation of a multiwavelength FDA. Spectral absorbance of liquids containing 10 ppb rhodamine-b are made and the sensitivity of the FDA compared with standard spectra-photometric techniques. The variation in returned signal as a function of drop growth phase obtained from three water based solutions are qualitatively investigated and the understanding of the measurement potential of the instrument system is discussed.

Impinging jets are used for heat and mass transfer in some industries. Previous impinging jet studies used thermocouples or liquid crystals to determine convection coefficients. These methods have inaccuracies that can be avoided with an infrared image temperature measurement. For this research, an infrared camera with a resolution of 0.025 degree(s)C was used to store images containing 52785 temperatures. The camera was checked for accuracy with a thermometer calibrated with a NIST standard. A facility for measuring surface heat transfer coefficients due to an impinging jet was developed. The infrared images obtained with the facility were used to identify impingement flow characteristics and to calculate local convection coefficients for in-line and radial jets. The results include photographs and convection coefficient graphs.

The application of liquid crystal thermography to the measurement of temperature/heat transfer in engineering is well established. Having gained practical experience in the use of liquid crystals for surface temperature and heat transfer determination, and the successful development and implementation of a digital image processing system for automatic analysis, their application has been extended to the simultaneous measurement of flow velocity and temperature by using a combined Liquid Crystal Thermography/Particle Image Velocimetry technique. Natural convection from a horizontal cylinder in an enclosure was chosen as the simple geometry to facilitate preliminary investigations. Water has been artificially seeded with micro-encapsulated liquid crystals and the natural convection flow field recorded on video to facilitate later analysis. By acquiring consecutive frames from the video the velocity magnitude throughout the flow field has been determined. The temperature field has been obtained from the same frames but using a manual technique.

The planned Space Shuttle Experiment STDCE-2 (Surface Tension Driven Convection Experiment) requires a non-contact Surface Deformation measuring instrument to monitor the shape of a dynamic fluid surface. This paper presents a conceptual design for this instrument which best satisfies the various science, engineering, and managerial constraints.

The European Space Research and Technology Center has developed a small, space qualified and TV compatible IR viewing system able to visualize thermal flows in fluids in microgravity. This instrument is a part of the diagnostics of a Spacelab facility, namely the Autonomous Fluid Physics Module (AFPM) flown on the last Spacelab 2D mission (April - May 1993). One of the main objectives of the research is to be able to monitor changes in the surface temperature of a fluid following the application of different stimuli. The only way to achieve this without disturbing the fluid under test is to use non-intrusive infrared measurement techniques. This paper describes the general design of the Thermal Mapping Diagnostic System and presents the technical solutions adopted to achieve the scientific goals of the investigation carried out with the AFPM.

In this paper, we used shapes of plasmas, which a Q-switched YAG laser acted repeatedly upon a CCD having MOS structure to produce, to investigate the destroying process of the optoelectronic device, and first obtained related experimental results of CCD to be destroyed by a 1.06 micrometers laser beam with a pulse width of 15 ns.

Production of surface pressure, plasma formation and momentum transfer of target is analyzed in interaction between laser and target material in this paper, a low-energy and high-power 1.06 micrometers YAG laser with a pulse width of 15 ns is applied to act upon different target material surfaces, and by using a pendulum shift technique to measure displacement of the target surface, momentum transfer and momentum coupling coefficient are obtained at different conditions.

High image density PIV is used to improve spatial resolution by ensuring that each interrogation spot gives a vector measurement. In this case the resolution is determined by the size of the interrogation volume. It is argued that the ultimate resolution of PIV is determined by the smaller of the mean spacing between particles and the displacement of the particles between light pulses, and that in the high image density limit, these distances are smaller than the interrogation spot size. Thus, it should be possible to improve spatial resolution to values less than the interrogation spot diameter. We refer to this as super-resolution. A method of achieving super-resolution by using a combination of correlation analysis of the group of particles in a spot and sub-interrogation spot particle tracking is described and evaluated.

Current emphasis on improving performance and reducing emissions in direct injection compression injection (Diesel) engines demands detailed understanding of high pressure transient sprays. Combustion studies require quantitative information, specifically local droplet sizes and velocities, throughout the spray field. The turbulent and unpredictable nature of the sprays complicates the analysis. Most tools currently available for spray analysis provide qualitative information over a large field of view or quantitative information at a single point in the spray field. This paper discusses the implementation of a diffraction-based diagnostic capable of determining particle size information over the full field. This diagnostic and particle image velocimetry together can provide a spatial map of local particle sizes and velocities in the spray.

Holographic particle velocimetry (HPV) is a promising technique for 3D flow velocity and hence vorticity measurements to study turbulence, coherent structures and vortex interactions. We discuss various aspects in the development of this technique ranging from hologram recording configurations such as in-line, off-axis and multibeam to data processing. Difficulties in implementation are analyzed and solutions are discussed. We also present preliminary measurement results in a 3D vortex flow using one of our prototype HPV systems.

A unique LDA system using a visible diode laser as the light source and an avalanche photodiode as the receiving detector is discussed in this paper. Experimental results with the system showed that under similar operational conditions, its signal to noise ratio is comparable to the results obtained using an Argon ion laser as the light source.

This paper introduces advances in LIPA (Laser Induced Photochemical Anemometry) and LIPA's application to the induction flow of a four-stroke internal combustion (IC) engine employing these advances. The IC engine is represented by a one-valve axisymmetric water analog model which was manufactured from quartz in order to achieve complete visual access since LIPA is an optical measurement concept. Two flow visualization techniques are used to obtain a qualitative picture of the induction flow. Reduction of LIPA data is done for the realization of the intake flow of one engine cycle at 20 RPM of obtain quantitative information of the flow field--velocity and vorticity maps for several crank-angles during the early phase of intake will be presented. These results which characterize the flow field in terms of fluid dynamic quantities are compared to the those results attained by flow visualization. A strong correlation between the two data sets (visualization and LIPA) will be denoted.

Conventionally, particle image velocimetry techniques utilize a laser light sheet oriented perpendicular to the viewing direction to illuminate tracer particles. In this SPIE proceedings paper, initial results are presented based upon illuminating the region of interest with partially coherent light from behind the particle and viewing the forward scattered diffraction pattern using video microscopy with a CCD array. There are several distinct advantages to this arrangement, including: easily identified particle centroids and the possibility of simultaneously obtaining the fluid velocity in different planes perpendicular to the viewing direction without moving the imaging system or illumination source. This technique will be referred to as Coherent Forward Scattering Particle Image Velocimetry.

This study examines some of the advantages and disadvantages of using far-field holographic recording to study velocity fields. Several important experimental design features are discussed and resolution and inherent signal-to-noise ratio problems are presented. Seeding requirements for determining velocity scales down to the Kolmogorov range are presented based on a Poisson distribution of seed particles. The source density, a measure of the seeding density, is restricted to values much less than one to achieve adequate holographic imaging. The limitations of particle motion during exposure required for adequate imaging are also assessed. The seeding density is limited by the desired measurable velocity range, according to particle tracking requirements. Experimental measurements of a velocity and vorticity field are presented, and the effects of seed density, particle motion, and tracking sequence on the velocity range are included.

Particle Image Velocimetry is now a well established technique for the instantaneous measurement of unsteady flow. However, two major limitations of the technique are the error suffered due to out-of-plane motion, and the use of time-consuming variable photographic processes to record the image. These limitations can be overcome by the measurement of the velocity components in all three dimensions and the use of solid state technology to record the image. The application shown in this paper, employed two CCD cameras connected to a PC- based imaging system, to record 3D PIV information. The major problems encountered were mainly related to the range required to image the region of interest (1.80 meters from the tunnel viewing window) and the synchronization and matching of the cameras; both in spatial characteristics and analogue electronics calibration.

Abstract not available.

As more and more applications for particle hologram have been developed, various methods for holographic image analysis have been studied. Being the preliminary task of holographic image processing, many analysis systems of 2D cross-sectional holographic field images have been developed. This presentation describes an on-line image processing system of particles auto-measurement for particle holograms. In this system, the 2D cross-sectional images of holograms are obtained using off-axis retrieval method. The whole processing task is divided into three sub-tasks. First, using an auto threshold selection approach, all the candidate particles are segmented. Then, the overlapped particles are separated and the basic parameters for the candidate particles are calculated. Finally, the candidate particles are verified using the parameters obtained above, and statistical data for the verified particles are worked out. At last, experiment results are given out to show the feasibility of this approach.

Recent metrological problems of the application of light scattering from solid particles of the dispersed solutions for the particle size distribution investigations, have been presented. The metrological analysis of the light scattering measurement at a small angle, has been worked out. It has been shown that, physical, mathematical, and metrological models of the measuring method and device, distinguished in the investigation process, and their evaluation from the measurement point of view constitute an integrating factor at interdisciplinary investigations of the particle size of the dispersing systems.

Photogrammetry, the measurement of three-dimensional object coordinates from stereo photographic images, is an essential element of 3D PTV. Ray tracing is the method that has been used traditionally, however it requires accurate knowledge of image distance, camera locations relative to the object field, and the size, shape, and refractive index of intervening elements such as apparatus windows. These parameters need not be known if one uses an optical transform and in situ photogrammetric calibration. the use of this technique significantly reduces the computational time required for 3D PTV and increases the accuracy of the measured velocity fields. This technique has been integrated with two others we have recently developed: one is 2D particle tracking using the concept of `path coherence', and the other is stereo matching based on 2D `particle tracks' rather than the particles themselves.

Particle Image Velocimetry (PIV), has been used to make 2D velocity measurements over the cylinder cross section of a reciprocating internal-combustion engine. Electrooptical image shifting has been demonstrated previously as a viable means to remove the directional ambiguity inherent in PIV. A two-laser system was developed to produce two, colinear, cross- polarized laser beams, which are required for the image shifting technique. Particle scattering resulted in some depolarization of the laser light. This was shown to result in erroneous vectors and a zero bias at low velocities. Techniques to minimize the depolarization problems are discussed. It is demonstrated that the uncertainty in this method is small enough to permit resolving in-cylinder engine turbulence.

Particle Image Velocimetry (PIV) is increasingly used to investigate unsteady velocity fields instantaneously. At DLR an experimental setup for PIV has been developed which can be operated in transonic flows under the rough environmental conditions (noise, vibrations) of a large high speed wind tunnel. This PIV-system has been successfully applied to flow field measurements in the velocity range from U equals 10 to 500 m/s. The evaluation and post processing of the PIV recordings runs fully automatical on a workstation. Two different aerodynamic investigations of instantaneous transonic flow fields around a bluff cylinder and around a NACA 0012 airfoil have been performed in a blow-down wind tunnel. The experience gained during these experiments and some technical improvements of the PIV technique which are necessary to enable its application in transonic flows are described.

The last two decades have seen rapid developments in computing taking as their inspiration the human brain. The human brain functions in a highly parallel and distributed fashion. The adaptive structure of the brain means that learning or training can accompany decision making. This basic neural model has inspired computer hardware exhibiting a parallelism which has revolutionised processing speeds in complex task analysis. Similarly there has been substantial activity in the field of intelligent software and in particular in the area ofneural computing. The human brain may viewed as composed of approximately 1 dbasic units, the neurons. Each neuron exhibits a high degree of interconnectivity with connections to approximately 1 O other neurons. Each neuron accepts many inputs which are added or integrated in some fashion and this causes the neuron to become active or passive. The active neuron emits an output to interconnected neurons. The importance of any one input is controlled by the effectiveness of the corresponding interconnection or weight. One area that has attracted attention in the application of neural networks is pattern recognition. Here the functions of feature classification and extraction are handled by a network which receives some education or training prior to the task of recognition. A priori knowledge of expected outcomes is used as a starting point with the network being allowed to modify or enlarge its knowledge base as the task proceeds. Various models or approaches to adaptive problem solving have been developed. The pattern recognition problem considered in the present paper is the identification of image grouping in double exposure PIV images. The aim is to provide an adaptive net which, following initial training, is able to identify image partners and adapt to changing flow conditions. This latter feature is seen as essential in order that the full potential of the neural net in temporally or spatially changing flow regimes can be realised. An important class of neural network is the multi-layer perceptron. The neurons are distributed on surfaces and linked by weighted interconnections. In the present paper we demonstrate how this type of net can developed into a competitive, adaptive filter which will identify PIV image pairs in a number of commonly occurring flow types. Previous work by the authors in particle tracking analysis (1, 2) has shown the efficiency of statistical windowing techniques in flows without systematic (in time or space) variations. The effectiveness of the present neural net is illustrated by applying it to digital simulations ofturbulent and rotating flows. Work reported by Cenedese et al (3) has taken a different approach in examining the potential for neural net methods applied to PIV.

Quantitative and visual data of artificially forced instabilities have been acquired in a flat plate boundary layer in air. For the first time the Particle Image Velocimetry (PIV) allows the recording of a complete velocity field instantaneously. With this technique quantitative data have been obtained within the boundary layer also very close to the wall. By using a light sheet technique it was possible furthermore to obtain visual data. Reproducible and constant conditions in the development of the instabilities are achieved by forcing the boundary layer with well controlled disturbances. These disturbances are generated with an arrangement for acoustic excitation.

Particle tracking velocimetry (PTV) is a well-known technique for the determination of velocity vectors in an observation volume. Here we present a fully automatic and efficient PTV method, which is based on the photogrammetric determination of particle coordinates in space. By this method we are able to determine about 100 vectors with satisfactory accuracy in an observation volume with a frequency of 25 time frames per second.

A description is given of the general aerodynamic features of the wind turbine. The complexity of the wake and the difficulties in adequately modelling the flow mean that full scale measurements are essential for its further development. Pulsed laser sheet velocimetry has been used in obtaining instantaneous flow field measurements around wind turbine blades. Wake measurements have also been obtained. Wind tunnel experiments are described in which a pulsed laser was synchronized with the turbine rotation in order to obtain phase sampled measurements. The estimation of derived quantities, such as angle of attack and circulation, is discussed. Procedures and techniques being adopted in outdoor tests are described.

Two methods of extracting velocity vectors from particle image patterns are described. The results are compared with Particle Image Velocimetry using the well established cross- correlation technique for a case of natural convection from a heated tube submerged in a water bath. In an endeavour to improve the accuracy of velocity extraction, velocity gradients have been introduced into the algorithm. The procedure is repeated to a chosen iterative limit. Results presented show the effect of the gradient operator on the velocities obtained in regions where the velocity gradient is large.

Representative classes of unsteady separated flows are interpreted using high-image-density particle image velocimetry,l which allows determination of the instantaneous, sectional streamline patterns and distributions of vorticity. Comparison of these instantaneous realizations in two orthogonal planes reveals fundamental mechanisms of distortion of the vorticity concentrations. Furthermore, by acquiring successive images closely spaced in time, it is possible to construct 3D volume representations of iso-vorticity. These quantitative approaches reveal limitations of interpreting patterns of instantaneous and ensemble-averaged flow structure.

The quantitative whole field flow visualization technique of PIV has over the last three years been successfully demonstrated for transonic flow applications. A series of such measurements has been made at DRA Pyestock. Several of the development stages critical to a full engine application of the work have now been achieved at DRA Pyestock using the Isentropic Light Piston Cascade test facility operating with high inlet turbulence levels: (1) A method of seeding the flow with 0.5 micron diameter styrene particles has provided an even (1 mm by 1 mm) coverage of the flow field. (2) A method of projecting a 1 mm thick high power Nd/YAG laser light sheet within the turbine stator cascade. This has enabled a complete instantaneous intra-blade velocity mapping of the flow field to be visualized. (3) Finally, software has been developed to automatically analyze the data.

The flow field around an axi-symmetric blunt nose cylinder-flare model has been studied experimentally using a holographic interferometry system with digital image post-processing. The model was placed in a supersonic flow field at a Mach number of 2.95 and at angles of incidence between 0 degree(s) and 20 degree(s). The results have been compared to inviscid flow calculations with a 3D Euler code.

Tomographic reconstruction from both interferometric and absorption data is a potentially powerful tool for experimental observations of compressible fluid mechanics, combustion, and heat transfer. In many of these cases, both flow field images and ensemble statistics are desired. The use of an ensemble of noisy tomographic data sets to synthesize image statistics and stabilize individual reconstructions using a Maximum A Posteriori (MAP) reconstruction technique is presented. The MAP technique uses the ensemble mean and variances of the source function to constrain individual reconstructions of the ensemble. In this paper, we show that by synthesizing the mean and variances using preliminary algebraic reconstructions, the reconstruction of the individual realizations can be improved. The technique is demonstrated using a group of source images generated with a fractal sum of pulses technique. The paper discusses a fractal model for turbulent mixing field images, the selection of the preliminary reconstruction technique, and the results of MAP and synthetic MAP reconstructions.

A technique by which ultrasonic waves are visualized is described. The method uses double- exposure holographic interferometry using iron doped lithium niobate crystals as the storage medium. These photorefractive crystals are self-developing, erasable and reusable, making them attractive for interferometry applications. This paper presents results of: (1) ultrasonic field parameters determined using the holographic method such as ultrasonic wavelength, and true resonance frequency of the transducer, (2) an example of image enhancement using image-substraction by phase modulation, and (3) initial results of visualization of ultrasonic wave fronts using a Nd:YAG laser.

Phase shifting techniques are often used to increase the precision of measurements made by holographic interferometry. These techniques use dual reference beams whose relative phase can be controlled precisely during reconstruction, usually through the use of piezoelectric transducers, tilting plates, or liquid crystal devices. This paper presents a simplified phase shifting technique which relies only on a standard micrometer screw translation table. Besides its simplicity, this technique also has the advantage of being light efficient. Many dual reference beam interferometers waste half the laser power in the reference beam splitter; this arrangement eliminates that waste. Results of a study in which this phase stepping technique was used in combination with a multi-pass holographic interferometer to measure the energy transferred from a spark to the surroundings gases are presented.

In this paper, the concept of directional smoothing is introduced and its application to interferogram noise reduction is presented. Interferograms provide isophase lines, that is, fringes and they thus contain directional information. In essence, the method incorporates this valuable directional information of interferograms by setting up a slender mask of relatively large aspect ratio along a fringe. The new value, that is, the average or median intensity of the pixels within the slender mask is assigned to each pixel. The slender mask could be straight or curved. For a straight slender mask, one should find the average direction of fringes within a certain chosen region. For a curved slender mask, the mask is set up along the fringe direction and may vary for each pixel. Based on computer simulation of experiments, the results appear to be promising as compared with ordinary smoothing or median filtering.

Artificial neural networks are suitable for performing pattern-to-pattern calibrations. These calibrations are potentially useful for facilities operations in aeronautics, the control of optical alignment, and the like. This paper compares computed tomography with neural net calibration tomography for estimating density from its x-ray transform. X-ray transforms are measured, for example, in diffuse-illumination, holographic interferometry of fluids. Computed tomography and neural net calibration tomography are shown to have comparable performance for a 10 degree viewing cone and 29 interferograms within that cone. The system of tomography discussed is proposed as a relevant test of neural networks and other parallel processors intended for using flow visualization data.

We describe the development of fiber optic sensors to measure heat flux and unsteady temperature in wind tunnel experiments for turbomachinery applications. The sensors are intrinsic Fabry-Perot interferometers fabricated from single-mode optical fiber. The optical path length within the interferometer fiber is sensitive to temperature. We present results from three sensors embedded as calorimeter gauges in a ceramic nozzle guide vane end wall model exposed to a transient heat flux in wind tunnel experiments and validated by comparison with previous data from platinum thin film resistance gauges. The optical sensors exhibit high spatial resolution (approximately 5 micrometers ), high heat transfer resolution (approximately 1 kWm^-2), and wide temperature measurement bandwidth (100 kHz) with intrinsic calibration. No electrical connections to the measurement volume are required and multiplexing is possible. Very short length (< 60 micrometers ) fiber sensors have been constructed and demonstrated as fast response thermometers suitable for measuring gas total temperature fluctuations in unsteady flow fields. We show results from a vortex shedding experiment from a heated bluff body in continuous flow generating temperature oscillations at 3 kHz.

Abstract not available.

A technique for determining the total mechanical impulse and the reactive force of an incipient non-stationary gas flow, on evidence derived from interference cine films, allows a reconstructive tomographic problem of reconstructing velocity and pressure fields in such objects to be formulated. This concept allows the distribution of velocity and pressure fields in such flows to be determined. The potentialities of the concept have been taken advantage of in estimating velocity and pressure fields arising on ignition of a premixed gas by a heated point body.

The interrogation analysis of digital PlY images with low pixel resolution is investigated analytically. It is demonstrated that the minimum required sampling rate for PlY images is about 1/4 of the sampling rate that matches the optical bandwidth of PlY imaging optics; a further increase of the sampling rate does not improve the accuracy of the estimated image covariance. The accuracy of a centroiding ( "center-of-mass" ) estimator and a curve-fitting ( "Gaussian-fit" ) estimator for the particle-image displacement is evaluated. It appears that the estimated displacement is always biased, as a result of the fact that the image covariance is estimated from a finite number of samples. The proposed correction procedure adequately compensates for this bias. The predicted performance of the displacement estimators is in fair agreement with the results obtained from measurements of a linearly displaced test object.

Holography is a method by which information of a 3D object space can be recorded. Used to record the position of neutrally buoyant tracers in a flow at two or more briefly separated instants it provides the means to record complex 3D velocity distributions. The magnitude of data contained in a holographic recording and the complexity of extracting flow displacement values from within a random distribution of holographically recorded seed particles makes automated analysis desirable. The analysis system described here is based on 3D correlation processing and provides an accurate and reliable means of detecting and measuring the local 3D displacements from a background of randomly positioned particles.

A hardware implementation of a Particle Image Velocimetry (PIV) system, used for 2D flow field analysis, is described. This implementation incorporates a 2048 X 2048 imaging CCD camera to replace photographic film and film scanners used in other PIV implementations. Use of this camera with an array processor and specialized software allows for the near real-time presentation of PIV data at resolution approaching film. PIV system control of both pulsed illumination and camera acquisition is accomplished via a windowed user interface running on a PC compatible computer. Novel approaches to resolving both velocity direction and zero velocity measurements are presented.

A newly conceived technique, termed holographic diffraction image velocimetry, has been investigated computationally and experimentally. The technique can capture 3D three- component velocity fields from a single observation direction. It is based on double-reference- beam double-exposure off axis holography. The independently reconstructed images are then analyzed by applying a cross-correlation technique with transplacing windows. The technique can offer experimental freedom and performance enhancement as compared with conventional techniques in addition to its ability for measuring 3D three-component velocity fields.

Non-penetrative thermal convection in a large-aspect-ratio container of water has been studied using stereoscopic Particle Image Velocimetry (PIV) to measure 3D velocity vectors in planar domains. The unique aspects of this work are the application of stereoscopic PIV in highly turbulent flow with significant small-scale energy, and the application of a liquid-filled test section which requires significant corrections for aberrations. Velocity data were obtained for three different cases of non-penetrative convection, corresponding to convective velocities, w_*, of 3, 4, and 5 mm/s. For each case, a sequence of about 20 pairs of stereo- photographs were recorded in a vertical plane, with sufficient time separation between photographs to ensure statistical independence at least for the turbulent motions with time- scales on the order of z_*/w_*. The grid-spacing of the resulting velocity fields was adequate to resolve the smallest structures in the flow.

In order to realize the high speed analysis in the incoherent high particle density PIV (IHD- PIV), the further advancement in both hard and soft wares is expected. Assuming the high resolution digital pictures, a new algorithm for the PIV is proposed. Although, spatial resolutions of existing video cameras are not sufficient for the PIV, the device is still useful for the purpose, since its the real-time recording and the future advancement is expectable. Assuming that a lot of tracer images are not clearly separated in the PIV pictures on a low spatial resolution medium, a new algorithm is developed which is based on the binary-image correlation method and the velocity vector histogram method. The whole analysis process could be performed by a personal computer and its can be finished in practically short seconds.

This paper describes the characteristics of the falling particles velocity in the air with the image analysis. Glass beads in a mean diameter 200 micrometers were dropped from an exit of a small nozzle. An application of a new image analysis such as a spatial filtering method based on dynamic image processing with a sequential image data obtained by a high speed video system was carried out. A specified frequency was obtained by the spectrum analysis with the reduced signals. Once a specified frequency was reached, we could calculate the velocity of a particle using the following equation, Vo equals f X (lambda) . These values were compared with the other values obtained by the optical fiber sensor method which was dual light source/receiver type sensor. Consequently, there were slight differences between them.

Since particle holograms are capable of the instantaneous recording of 3D field particle, a lot of holographic recording and analyzing systems have been developed for various particle field analysis applications. This presentation describes an image pre-processing for particle holograms. First, a directed graph (DG) is defined and converted from a image. Second, four types of vertex are defined according to the relationships among vertexes in DG, then a gradient flowing graph is constructed from DG to obtain a set of gradient demarcation vertexes (DGV). Finally, the gradient dividing line is generated by the set of DGV, and the region of interesting (ROI) including particles and fewer noises is obtained; the histogram of ROI has more obvious bi-peak character than that of whole image. Therefore, it is easy to select thresholds for generating binary image and to obtain basic parameters on particles.

Fuzzy logic has proven to be a simple and robust method for process control. Instead of requiring a complex model of the system, a user defined rule base is used to control the process. In this paper the principles of fuzzy logic control are applied to Particle Tracking Velocimetry (PTV). Two frames of digitally recorded, single exposure particle imagery are used as input. The fuzzy processor uses the local particle displacement information to determine the correct particle tracks. Fuzzy PTV is an improvement over traditional PTV techniques which typically require a sequence (> 2) of image frames for accurately tracking particles. The fuzzy processor executes in software on a PC without the use of specialized array or fuzzy logic processors. A pair of sample input images with roughly 300 particle images each results in more than 200 velocity vectors in under 8 seconds of processing time.

In this paper, the application of laser speckle photography in study of convective heat transfer is presented in detail. Six kinds of experimental system of laser speckle photography and two methods of reconstruction of specklegram are proposed. The measurement principles and the formulas of experimental data processing for determination of 2D and axisymmetric temperature fields by using laser speckle photography are described. For illustration, the laser speckle photography has been used to study heat transfer of natural convection thermal boundary layer in a heated isothermal vertical flat plate and that between two heated vertical plates. The natural convection cooling of a heated vertical strip has also been studied by laser speckle photography.

Optical tomography using interferometric data is applied in this study to investigate the flow and heat transfer phenomena a 3D differentially-heated cubic enclosure. The interferometric recording and reconstruction system, associated processing and reconstruction procedures, and results from this analysis are described. The experimental results are verified by comparison with independent temperature measurements. The comparisons indicate that the experimental technique can yield 3D perspectives of complex flows having sufficient spatial resolutions to verify detailed 3D direct numerical simulations.

Abstract not available.