The results of an experimental investigation of isothermal swirling flows in a model of a coaxial dump combustor are presented. A set of three constant angle swirlers were designed and fabricated for this aspect of the study. A two component LDV system was used to obtain the velocity measurements of the flowfield. The detailed data base is provided for the development of turbulent closure models and the CFD code validation for the ramjet or turbojet applications. The results show the effects of the swirl strength on the flow characteristics, enhanced turbulent mixing and the resulting shortened corner recirculation zone.

A fast analog optical method for evaluating Doppler bursts is presented. The method uses an optical 2D Fourier processor and a spatial light modulator. Two different setups for evaluation of Doppler bursts are described. The method reduces considerably the time needed for evaluation and the setup cost is reduced compared to computer-based burst analyzers.

This paper examines the adaptation of low-cost Schmidt-Cassegrain astronomical telescopes to perform the laser-beam-focusing and scattered-light collection tasks associated with dual-beam laser Doppler velocimetry. A generic telescope design is analyzed using ray-tracing methods and Gaussian beam-propagation theory. A straightforward modification procedure to convert from infinite to near unity conjugate-ratio operation with very low residual aberration is identified and tested with a 200-mm-aperture telescope modified for f/10 operation. Performance data for this modified telescope configuration are near the diffraction limit and agree well with predictions.

With the realization of optical fibre technology for transmission of high light power new possibilities for configuration of optical systems for LDA measurements are coming up. The increased flexibility of the systems have in the first years of the fibers mainly been used to make the measuring probe smaller. The standard dimension today for these probes is 14 mm. The focal length is around 50 mm. These probes are very well suited for wind tunnel measurements, if the windtunnel is provided with a high quality traversing system, and the blockage of the probe and the traversing system can be accepted. In many situations this is not the case, so there is still a requirement for LDA systems with long focal length, so the optical set-up can be outside the tunnel. Until now this has caused problems due to large required aperture even for one dimensional systems. The size and weight of the system has increased to dimensions impossible to handle and traverse, or they have had insufficient apertures, and therefore suffered from poor signal quality. The problems increase further if two and specially three component systems are generated. The result has been systems, that are difficult to align and to operate, poor resolution and poor signal quality. With the fibre technology many, although not all of these problems can be overcome. This paper will describe new concepts, that although many of them are based upon old ideas, first have come to a mature state now from an engineering point of view. The paper will both describe the theoretical advances by these new concepts, but also some practical examples of realization will be included. The main problem with the long range systems, where several have been built almost from the beginning of LDA technology has been the requirement for the large aperture if a single lens system should be used for both transmission and reception, or the complication in mirror systems for individual transmission beams if individual transmission beams were used. The fibre technology will overcome these problems and add further benefits.

The role in flow research of the Laser-2-Focus velocimeter, also known as the Laser Transit Velocimeter, is discussed. This technique measures the time of flight of small tracer particles as they cross an optical gate formed by two highly focused laser beams. It is applicable to study laminar flows in different directions. The physical properties of the technique are outlined and compared to those of the laser Doppler technique. The relation between measurement time and turbulence intensity is estimated and solutions are proposed that make the L2F technique suitable for measurements in flows of higher turbulence intensities.

Particle image velocimetry (PIV) is applied here to gaseous and liquid flows including an impinging jet in an atmospheric microburst, gaseous turbulent flow in an internal combustion engine, and turbulent channel flow. The resulting velocity distributions are shown and discussed.

Synergizing laser speckle velocimetry (LSV) or particle image velocimetry (PIV) with finite-element smoothing is shown to be a highly effective means of determining the derivatives, divergences, and vorticities of a flow field. A ''pseudo'' finite-element technique is used to smooth and differentiate discrete 2D velocity field data generated by the pointwise analysis of an LSV or a PIV specklegram. This technique is shown to be significantly more effective than either a 1D cubic spline technique or a straight finite-difference technique.

An optical technique for analyzing particle image velocimetry data has been demonstrated on a variety of particle patterns from actual flows and from similar translate diffuser experiments. The technique uses point-by-point illumination of the particle image and two subsequent 2D FFTs to produce an autocorrelation pattern of the particles from which the particle displacement is determined. The dynamic range in the technique''s configuration is about 30:1, with reasonably good processor speed.

Methods of resolving directional ambiguity in PIV flow measurements are reviewed. Emphasis is given to the use of image shifting by mirror and laser pulse ''tagging''. Sample images obtained by these techniques are presented and the applicability and limitations of the image shifting approach are described.

A novel method for determining two-dimensional velocity flowfields has been developed. The technique, two-color particle-image velocimetry (PIV), is similar to existing PIV techniques except that two different-color laser sources are used to form the light sheets required for exposing the position of particles in a seeded flowfield. A green-colored laser sheet (formed by a doubled Nd:YAG laser) and a red-colored laser sheet (formed by Nd:YAG-pumped dye laser) are employed sequentially to expose the particle positions which are recorded on 35-mm color film. Analysis of the resulting images involves digitizing the exposed film with color filters to separate the green- and red-particle image fields and processing the digitized images with velocity-displacement software. The two-color PIV technique has the advantage that direction, as well as particle displacement, is uniquely determined because the green-particle image occurs before the red one by a known time increment. Velocity measurements utilizing the two-color PIV technique on a propane jet diffusion flame have been made and are discussed.

An optical real-time holographic autocorrelator for the processing of multiple exposure images in particle image displacement velocimetry is presented as a powerful alternative to conventional processing devices. This device is based on a Bi12SiO20 spatial light modulator and can result in processing rates as high as 100 frames per second. The limitations inherent to its operation are theoretically derived and some limits are given on the digital image processing algorithms used to analyze an autocorrelation pattern for deriving velocity information.

A method for evaluating particle image velocimetry (PIV) recordings by means of an analog optical processor utilizing a spatial light modulator is proposed. A prototype of such a setup has been tested and the successful evaluation of PIV recordings has been demonstrated.

The accuracy of the Particle Image Velocimetry technique was investigated using synthetic images having known characteristics. Algorithms were developed to process images automatically without operator assistance. This allowed to parametrically investigate the influence of the various parameters (image contrast, image noise, particle density, distribution of sizes of particles and particle displacement between frames) on the accuracy of the technique. It was found that as long as the images have a good contrast, particle locations can be determined with sub-pixel accuracy and particle velocities can be determined within a few percent.

An analytical model and a computational simulation of a double-pulsed planar particle image velocimetry (PIV) system are used here to optimize the performance of PIV for a full 2D interrogation by either spatial correlation or Young''s fringes. The similarity between correlation methods and full 2D Fourier transform methods is outlined, and differences between the optimal parameters for each method are explained. The mean properties of the spatial autocorrelation function and the Fourier transform of the Young''s fringes are developed both theoretically and using analytical models based on experimental results.

Two new techniques for measuring spatially resolved features in high speed air flows are presented. Rayleigh scattering with ultraviolet light yields intensities which are high enough give instantaneous cross sectional images of atmospheric density air with a relatively low energy laser. These images freeze turbulent features and shock structure. They can be used observe shock wave! boundary layer interactions and to construct spatial correlations which show the average size and shape of these turbulent features as well as the correlated motion of shock structure. Using the RELIEF method, we are able to instantaneously write lines or shaped volume elements into the flow and interrogate them at a later time. This enables us to record instantaneous velocity profiles, each of which gives a frozen image of the turbulent motion of the flow. From numerous such images the average velocity, turbulence intensity and cross stream velocity correlation can be found.

Volumetric visualization is becoming an important research tool. The need to understand the complex three-dimensional structures contained in experimental and coniputational data volumes is driving the development of a wide range of new visualization techniques and tools. Animation is particularly important in aiding comprehension of diffuse volumetric structures. These are often nested within one another, and cannot be represented well in solid ol)ject illustrations. The enormous computational burden of producing animated illustrations of volumetric data is address by the AIM rendering technique described in this paper.

Laser diagnostics experiments are described for obtaining multi-dimensional measurements in turbulent flows and flames. Techniques for mapping scalar fields in two and three dimensions are described and examples of measured quantities are presented. Additionally, the temporal evolution of a three-dimensional gas concentration field was measured in an acoustically forced flow, essentially providing a four-dimensional measurement of the flow. A technique for extending this approach to measurements in more general turbulent flows is proposed.

Electronic imaging of laser induced fluorescence from a plane of laser light that intersects a reactive flow is becoming commonplace. Quite often, the fluorescence wavelength is longer than the laser excitation wavelength and hence the fluorescence is easily discriminated from the Rayleigh and Mie scattering, which is at the laser wavelength. In the case of resonance fluorescence, the fluorescence is sufficiently near the laser excitation wavelength that low fluorescent signals are obscured by Rayleigh and Mie scattering. However, recognizing that the fluorescence scattering is weakly polarized while the Rayleigh scattering light is strongly polarized suggests that a polaroid filter could improve the signal to noise by eliminating Rayleigh scattered light and passing half of the fluorescent scattered light. By rotating the polaroid filter, any amount of Rayleigh scattering and resonance fluorescence from CH as it occurs in the flame front of premixed methane flames.