Experimental Systems and Techniques

Experimental Systems & Techniques

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 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.

LASER SYSTEMS

A range of laser systems allows illumination of complex flows for techniques of high-image-density particle image velocimetry. Eight pulsed Yag lasers (35 mj to 90 mj) form four independent, dual pulsed Yag laser systems, which are employed in conjunction with digital particle image velocimetry (DPIV).

OPTICAL SYSTEMS

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).

IMAGE ACQUISITION UNITS

Digital particle image velocimetry is predominantly employed in our laboratories, and a total of five digital cameras are available. These cameras have a sufficiently high framing rate to employ cinema image acquisition in most of the flows pursued in our laboratories.

IMAGE PROCESSING AND POST-PROCESSING SYSTEMS

A total of six independent workstations are employed for extensive assessment of flow patterns acquired either using the digital version of high-image-density particle image velocimetry. Such post-processing includes not only the evaluation of, for example, patterns of vorticity and streamline topology, but also image enhancement and transformation, pattern recognition, and other state-of-the-art image processing techniques.