Ultrasonic Measurement of the Geometric Parameters of Gaseous Voids in Low Gravity Fluid Containers

to establish the location and shape of a Iiquid/vapor interface in a liquid container, thus enabling liquid A demonstration system for the ultrasonic gauging of volume measurement [I,21. fluids in low-gravity has been designed and tested. For purposes of simplification, it was assumed that vapor Typically, in propellant storage applications, the liquid within a liquid container in low-gravity would form a wets container walls so that a vapor bubble (or spherical bubble which would float freely in the bubbles) exists within the liquid [3]. The liquid/vapor container. The project was designed to show that interface acts as a nearly perfect retlector of sound ultrasonic tcchniques could be uscd to detcrmine the waves, so that it is then possible to project ultrasonic geometry of the resulting sphere given a worst-case waves into the liqUid, measure the retlected field using transducer arrangement. The motivation was to a transducer array, and compute the interface shape simplify transducer mounting requirements so that (and volume) from these data. propellant or other storage vessels could be fitted with ultrasonic gaging systems with a single or perhaps a A limitation of conventional ultrasonic imaging few transducer penetrations. Data was collected from schemes is that they require that the discontinuity a planar array of transducers. The high error expected retlcct energy diffusely; that is, energy is reflected in all due to the low triangulation was reduced by directions. Because the liquid/vapor interface maximizing the amount of data collected. This was approximates a perfect reflector, however, energy is accomplished using the transducers in both pulse/echo reflected in primarily one direction. Conventional and pitch/catch operational modes. ultrasonic imaging schemes, such as those used in medical fields in addition to requiring diffuse Introduction reflection, require a mobile transducer or several transducer arrays. The added complexity of such a A long standing measurement problem in fluid system would be ohjectionable especially with regard to mechanics has been the determination of liquid volume cryogenic storage vessels. Transducers mounted on all in low gravity wherein the Iiquid/vapor interface docs sides of a container would provide a high degree of not always occur at a consistent, locatable poSition. triangulation and therefore the high accuracy. The It has been proposed that ultrasonic imaging be used utility of such a system would be limited since access IStudent Member, AIAA. 2Member, AJAA. Copyright © 1990 American Institute or Aeronautics and 1 Astronautics, Inc. All rights reserved. to all sides of a vessel may be difficult or undesirable. Ideally, it would be desirable to be able to "view· the entire fluid space using a limited planar array, idealized in Figure 1. Transmitted sound, reflected from fluid­ vapor interfaces, would be received by other transducers whose signals would he analy7.cd to yield interface shapes and locations. It seems that there arc three basic requirements for ultrasonic imaging of a fiuid/vapor interface. The first is that a tcchnique must properly utilize the reflective properties of the interface. The second is that a small number of fixed transducers ought to be used. The third is that the transducers should be mounted in close proximity to each other, Le. a single array. The Objective of the work reponed here was to show the feasibility of using ultrasonics with specific geometry constraints; namely, the transducers were mounted in a planar array, Figures 2 and 3. To this end it was assumed that bubbles tend toward the minimum energy state, ie. a single large bubble [4,S}, and are free floating in the container [5}. Finally the assumption of sphericity implies that the bubble oscillations are damped [5,6).