Design and construction of a drop generator for use in a vertical wind tunnel

A drop generator, based on the principle of a vibrating capillary, was designed and built for use in the UMR vertical atmosphere wind tunnel. The drop generator worked very well on a test stand where it was firmly supported, but was not consistent when tested in the wind tunnel. Vibration of the wind tunnel walls and a slight turbulence near the forward edge of the generator caused an oscillation in the position of the stream of drops. The oscillation resulted in some of the drops hitting the edge of the collector cup, where the drops would accumulate until a large drop would form and fall. Smoke streamlines were introduced in the wind tunnel to test the air flow of the wind tunnel. With the drop generator in place but not producing drops the 1 mm diameter smoke streamlines could be observed in the 1 meter length of the test section without noticeable broadening or turbulence. However, with the drop generator producing drops the smoke streamlines were dispersed very quickly due to the turbulence. This turbulence, while the drop generator was in operation, was due to a partial blockage of the honeycomb section mounted in the flow straightener section. This blockage was due to accumulation of water in the small channels of the honeycomb. The wind tunnel would not support drops in its updraft, the fault being caused by turbulence introduced by the water-clogged honeycomb. More rigid support of the wind tunnel and adjustment of the drop generator would stop the large erratic drops, and therefore keep the honeycomb free of water. The observed smoke streamlines with a dry honeycomb indicate the flow should be adequate to suspend drops --Abstract, page ii