Grants from the Office of Naval Research, the National Science Foundation, the Air Force Office of Scientific Research, DARPA, the Volkswagen Foundation, and various industrial organizations have provided resources for construction of experimental facilities and acquisition of state-of-the-art instrumentation. We have recently developed new experimental systems and techniques, post-processing methods, and simulations, all of which are heavily dependent upon recent advances in computer technology. Unique types of experimental systems, with emphasis on three-dimensional access for quantitative flow visualization, have been designed and fabricated. Advanced microcomputer systems, continuous and pulsed laser units, and analog and digital camera systems have been acquired and form the basis for quantitative imaging of complex flows. Development of the foregoing experimental systems has led to construction of similar facilities at a number of universities and government laboratories in this country, as well as in England, Germany and Australia.
FLOW FACILITIES
Two large-scale water channels, specially designed for three-dimensional illumination and image acquisition, are employed for experiments involving steady inflow. A variety of test sections can be placed within the channels, in order to simulate interaction of turbulent and vortical flow fields with bodies, including cylinders, spheres, delta wings, and streamlined leading-edges. In addition, fully-developed turbulent boundary layers on flat plates and turbulent flows within channels are attainable through inserts into the main test section of the water channels.
A wave tank system, again designed specifically for three-dimensional laser illumination and image acquisition, generates waves of desired amplitude and frequency through use of a unique force feedback-controlled wave paddle (Edinburgh Designs, Ltd.). This system generates progressive waves, while minimizing contamination due to reflection effects, attainable with the feedback system.
A shallow water tank, constructed of high quality optical glass, allows examination of vortex flows that have a characteristic scale much larger than the depth of the water. This type of apparatus provides new insight into the relationship between instantaneous wall shear stress and vortical flow patterns above the wall.
An open-circuit wind tunnel provides uniform, low turbulence intensity inflow for examining attached and separated flows.
An acoustic resonator facility allows study of acoustic wave- unsteady flow coupling in various types of internal flow systems containing cavities. Optical access in three dimensions allows characterization of the physics of flow-acoustic coupling using quantitative imaging techniques.
LASER SYSTEMS
An extensive range of laser systems allows illumination of complex flows for techniques of high-image-density particle image velocimetry. Six pulsed Yag lasers (90 mj to 130 mj) form three independent, dual pulsed Yag laser systems, which are employed in conjunction with digital particle image velocimetry (DPIV). Two high-powered Argon-Ion lasers (25 watts) and five medium-powered Argon-Ion lasers (3 to 5 watts) are employed for high-resolution, film-based particle image velocimetry (PIV). In addition, two low-powered Helium-Neon lasers are employed for general purposes in our laboratories.
OPTICAL SYSTEMS
A total of four image-shifting mirror systems are employed to preclude directional ambiguity during acquisition of particle image patterns when using film-based techniques. The foregoing laser-based instrumentation involves a number of different types of optical trains, as well as spherical-cylindrical lens arrangements for beam focusing and conditioning, in conjunction with techniques of particle image velocimetry (PIV) and digital particle image velocimetry (DPIV). In addition, six different laser scanning units, which employ either multi-faceted rotating mirrors, or oscillating galvanometer driven mirrors, provide scanned laser sheets for PIV.
IMAGE ACQUISITION UNITS
For the techniques of film-based and digital versions of high-image-density particle image velocimetry, as well as for qualitative flow visualization methods, including dye, smoke injection, and the hydrogen bubble techniques, a variety of camera and lens systems are available.
For high-resolution, film-based PIV, a total of eight motor-driven, film-based cameras can be employed. They include 35 mm Nikon and Canon cameras and a Hulcher cinema framing camera, with a range of possible lenses.
For digital particle image velocimetry, four high-resolution digital cameras are available. In addition, the newly released four megapixel Kodak camera is used for selected applications.
IMAGE PROCESSING AND POST-PROCESSING SYSTEMS
Three digitizing systems, including two Nikon units and a Leaf unit, can be employed for digitizing patterns of particle images for the high-resolution, film-based particle image velocimetry. These digitizing systems are linked to two special-purpose workstations.
In addition, a total of fourteen independent workstations are employed for extensive assessment of flow patterns acquired either using the film-based or digital version of high-image-density particle image velocimetry. Such post-processing includes not only the evaluation of patterns of vorticity and streamline topology, but also image enhancement and transformation, pattern recognition, and other state-of-the-art image processing techniques. In addition to these systems, the local area network (LAN) provides a direct connection to Silicon Graphics and IBM workstations at other locations within the Department of Mechanical Engineering and Mechanics and across the Lehigh campus.