Howdy!!

Here is a brief tour of our fabulous laboratory. Although it is called LDA Lab at the moment, we do much more. It is located in Bldg 541, between Engineering II and Chemistry. The laboratory has two 3-D LDA systems, each powered by a 5W Ar-Ion Laser. The first LDA system that we acquired deserves special mention because its optical system was entirely designed and fabricated by Roni Plachta, an ex-graduate student and Martin Vandenbroek, our know-it-all laboratory engineer. The front optics of this LDA-system has been designed to minimize the effect of refraction so that it can operate with a probe volume of 50 cubic microns. It has been extensively used for measurements close to the wall and free-surface of turbulent channel flows. Currently it is being used by Xinsuang Nan, a graduate student in our lab, to study the phenomenon of wave-turbulence interaction in a horizontal channel of size 8m x 0.7m x 0.25m.

The other LDA system takes measurements is a slightly smaller horizontal channel of size 4.5m x 0.32m x 0.1m. This channel was designed by Daniel Kaftori. Danny carried out extensive experiments on Particle-Turbulence interaction in this channel with some very interesting visualizations of near-wall turbulence structure. More recently, this channel has been used to study the characteristics of free-surface turbulence in turbulent channel flows using flow visualizations (LIF and time-intergrated imaginging of micro-particles sprinked on the free-surface), and PIV (particle imaging velocimetry) measurements. These experiments have been performed by Sanjeev Kumar and Rohit Gupta. Digital images for PIV analysis have been captured by moving a digital camera (Kodak EktaPro6000 - which can capture images up to 6000 partial frames/sec), mounted on a computer controlled traverse (Daedal 20400 with 4-axis Compumotor indexer - AT6400), close to the speed of the free-surface. A high resolution PIV algorithm (we call it Hierarchical Particle Image Velocimetry - HDPIV) has been developed to get quantitative information from the digital images.

Rohit has recently constructed another channel which will facilitate experiments related to the interaction of structures produced near the bottom of a channel with the free-surface at high Reynolds numbers (~ 50,000). This channel, made of 2cm thick glass plate, is 3.5m long and 2m wide. Experiments are to be conducted at water depths of 0.5cm or less at Reynolds numbers higher than 50,000. At such high Re turbulent spots are seen at the free-surface, which are basically near-wall structures interacting with the free-surface. By flow-visualizations, quantitative measurements of the velocity field in these near-wall generated structures, and simultaneous measurements of the free-surface deformation, the experiment aims at providing detailed information on interactions between a free-surface and turbulence. Rohit is also working on another experiment to study the effect of particles on heat transfer at a solid-liquid interface. This experimental facility is also near completion.