New Flow Visualization Technique for Water Tunnel Testing of Combustors

摘要

A new technique for water tunnel flow visualization is based upon the use of a newly developed type of material--neutral-density, bi-liquid foams or 'polyaphrons'. These materials are small, spherical globules of one liqund encapsulated in a thin film of another liquid. It is now possible to make bi-liquid foams when the units are of micron or submircon size, and may be spherical or polyhedral depending upon the relative concentration of oil to water. They are easy to see and photograph in water and they can also be dyed to a variety of intense colors. In this two part study, polyaphrons were used for flow visualization in water tunnel tests of combustors. First, various formulations of the polyaphrons were made to optimize aphron size and density for water tunnel testing. Second, the best polyaphrons were used for flow visualization of real, prototype combustor model. Tests were conducted at 22.5 gpm. This corresponds to Re sub D=23,900, when D is the swirler diameter. Tests showed that polyaphron material proved easy to handle when injected through small tubes and the amount and ratio of injection was easy to control. No clogging of any kind was ever encountered. The pure material broke-up into clumps upon injection. A 50/50 mixture of water polyaphron eliminated clumping. Injection of polyaphrons was also directly compared with the more usual dye injection. Polyaphrons are ideal seeding material for Laser Doppler Velocimetry in water tunnels.