VORTEX INHIBITING TANK OUTLET STRUCTURE

Abstract: Spherical tank (30) has its outlet (34) angularly positioned away from the tank center line axis (54) which is parallel to the local gravity vector (26). This angular positioning of outlet (34) inhibits vortexing as liquid is withdrawn from tank (30).

Description: VORTEX INHIBITING TANK OUTLET STRUCTURE BACKGROUND OF THE INVENTION This invention is directed to a vortex inhibiting tank outlet structure wherein the tank outlet is positioned away from the local gravity vector in the tank. When the tank is used to supply liquid, the ingestion of vapor from over the liguid into the liquid outlet line may cause serious problems. In one case, where the tank is pressurized with an inert gas and liguid fuel is supplied from the tank outlet, the ingestion of pressurizing gas into the outlet line is serious and may cause flame-out where the fuel is burned, leading to overheating, chugging and possibly explosion. Prior efforts led to the conclusion that anti- vortexing baffles were the best solution to the problem, and these were universally adopted. However, different problems occur in zero and low gravity force operations. In spinning spacecraft, it can be argued that a coriolas-type moment is produced by an interaction of fluid motion moving radially inward towards the drain, combined with the angular-spin rate. This moment could be the driver in the vortexing, but this is difficult to gualify. Other possibilities of swirl initiation are angular rates left over from satellite orientation and random inputs caused by orientation correction pulses. These possibilities become particularly apparent in space¬ craft structures where the local gravity force is either OMPI zero or much smaller than earth gravity, but the same concepts apply to earth-bound tanks. Such earth-bound tanks in a 1 G environment can also benefit from the invention defined herein. Accordingly, there is a need for a means for inhibiting vortexing at the outlet of a tank structure. SUMMARY In order to aid in the understanding of this invention, it can be stated in essentially summary form that it is directed to a vortex inhibiting tank outlet structure wherein the tank outlet is angularly oriented with respect to the local gravity vector. It is thus a purpose of this invention to provide a structure which inhibits vortexing at a tank outlet. It is another object to provide a tank outlet which is angu¬ larly oriented away from the local gravity vector within a tank so that the outlet is not at the "bottom" of the tank and is also angularly positioned with respect to the vector. It is another purpose to provide a' vortex inhibiting tank outlet structure which can be employed without taking up tank volume, or get in the way of internal tank struc¬ tures or internal tank flows-. Other purposes and advantages of this invention will become apparent from a study of the following portion of this specification, the claims and the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of the satellite in space where the vortex inhibiting tank outlet structure of this invention may be employed. FIG. 2 is a section taken generally along line II-II of the satellite of FIG. 1, but showing the satellite antennas in the stowed position, with parts of the satel¬ lite structure broken avay. O PI FIG. 3 is a center line section through a tank and its outlet in accordance .with the prior art. FIG. 4 is a center line section through the tank of this invention, showing its outlet " away from the local gravity vector. DESCRIPTION OF THE PREFERRED EMBODIMENT Satellite 10 shown in FIGS. 1 and 2 has a cylindri¬ cal spinning body 12 which is illustrated as being covered with solar cells to supply the electric power requirements of the satellite electrical systems. The deεpun platform 14, see FIG. 1, is rotatively mounted with respect to the spinning body 12 and rotates with respect thereto so that .antennas 16 and 18 mounted thereon can be directed as desired. Quite often the antennas are directed toward earth. In FIG. 2, the antennas 16 and 18 are shown in the stowed position, for economy of drawing. Spinning body 12 has an interior frame 20 on which the various parts are mounted. The spinning body 12 rotates on axis 22 to pro- duce a radially outward accerational force from that axis. Vectors 24 and 26 represent the radially outward local G force, which usually is a small fraction of the earth's gravity acceleration. Tanks 28 and 30 are spherical propellent tanks formed of a structural shell which constrains the internal tank pressure and defines the tank as a vessel which has a volume. The tanks respectively supply liquid propellant out of outlets 32 and 34 to propellant lines 36 and 38. The lines are connected through suitable control valves to thrusters which are oriented in various directions to be used for attitude control and station keeping. Thrusters 40 and 42 are illustrated and there are usually sufficient thrusters to control attitude on three axes. Sometimes, station keeping thrusters are also supplied from the same fuel propellant system. The -propellant may comprise two liquids in a bipropellant system or the single liquid in a monopropellant system. Since there is a local gravity vector resulting from the spinning of body 12, no bladder or other mechanical expulsion device is necessary for the expulsion of fluid from the tanks. In FIG. 4, the local gravity vector is indicated at 26. In the prior art tank 44 illustrated in FIG. 3, the tan outlet 46 was on a central axis 48 through the tank which was parallel to the local gravity vector 26. In other words, outlet 46 was at the bottom of the tank, directly on the tank axis. In view of this gravity vec- tor, withdrawal of the propellant liquid 50 from the tank caused a vortex 52 to form. In view of the very low acceleration along the vector 26, even when there is a substantial amount of liquid 50.in the tank 44, due to the vortex, pressurization -gas or vapor over the liquid may be discharged out of the outlet 46. This invention overcomes the vortexing problem. The tank 30 of this invention is illustrated in FIGS. 2 and 4, and it has an outlet 34 which is positioned away from the center line axis 54- of tank 30 which is parallel to the local gravity vector 26. While is has been shown that * angular positioning of outlet 34 away from axis 54 o from 1 upward is operative, an angle of 10° between the axis 50 and outlet 34 as considered preferable. This angle is small enough that little unused liguid is left in the bottom of tank 30, but the angle is larger than the minimum 1° angle required to inhibit vortexing. As illustrated in FIG. 4, the tank 30 is formed of a spherical shell and axis 54 passes through the geometric axis of the spherical shell. Axis 54 is parallel to the local gravity vector.26. Outlet 34 is secured to the tank shell and forms the tank outlet structure, which is part of the tank in accordance with this invention. As indi¬ cated in FIG. 4, outlet tube 34 is " away from axis 54. It has been found that so much as a 1° separation of the out¬ let 74 from the axis 54 has a substantial effect on vortex inhibition. However, for mechanical safety, the outlet 34 is positioned from 5 to 10° away from axis 54. Thus, the angle of effectiveness is as little as l β , and when the angle gets up into the region of 15 β the amount of liquid left in the spherical tank below the outlet becomes exces¬ sive. Therefore, a more limited and more preferred range of angularity of the tank outlet structure is from 5 to 10°. There are a plurality of mechanisms which provide some propellant angular momentum around the tank center line radial vector 54 which is normal to the spin axis. The most likely generating functions are motion amplifica¬ tion due to boundary layer interactions associated with curved streamlines, and irrotational inphase sloshing, driven by spin axis nutation, turning into reversing- periodically-rotational flow. In addition, there is a coriolaε type moment produced by an interaction of fluid moving radially outward towards the drain combined with the spin angular rate. Other causal possibilities of swirl initiation are angular rates left over from the orientation maneuvers, and ra dom inputs caused by a series of station keeping pulses. These factors are not well understood, and as a result it becomes impossible to eliminate the vortexing by eliminating the causes. The present tanks are spherical, principally for their favorable weight versus volume and pressure handling ratios, but the considerations also apply to any tank which is a section of revolution around an axis which vϊP r * -VATlO extends in the gravity vector direction. Baffles can be used, but they cause a pressure drop and add weight to the structure. However, the positioning of the tank out¬ let away from its center line on the gravity vector is equally capable of inhibiting vortexing in tanks which are non-spherical tanks which are not surfaces of revolu¬ tion and tanks where the.outlet is not on the center line. As expected, higher flow rates produce stronger vortexing. However, the vortexing phenomena was found to be indepen- dent of fraction of tank fill, direction of initial fluid rotation, tank pressure variations and kinematic viscosity of the liguid. Decreases in outlet tube diameter cause stronger vortexing due to increased flow velocity. Thus, improved vortex inhibition is needed where the vapor or pressurizing gas over the liquid in the tank should not be delivered from the tank outlet at least until the tank is empty of liquid. This invention has been described in its presently contemplated best mode and it is clear that it is suscep- tible to numerous modifications, modes and embodiments within the ability of those skilled in the art and without the exercise of the inventive faculty. Accordingly, the scope of this invention is defined by the scope of the following claims. OMPI

Claims: AMENDED CLAIMS (received by the International Bureau on 5 April 1982 (05.04.82)) What is Claimed is: (amended) _. p_ closed spherical tank for the storage and discharge of liquid in an environment having a gravity vector, said tank comprising: a closed spherical tank shell enclosing a spherical tank volume for the containment of liquid, said tank having an axis through the center of said tank and in line with the local gravity vector; said closed spherical tank having an outlet comprising an opening in said closed spherical shell and an outlet tube connected to said opening for discharging liquid from said closed spherical shell of said tank, the improvement comprising: said outlet being angularly away from said spherical tank center line axis in line with the local gravity vector to inhibit vortexing in liquid being discharged from said spherical tank out of said outlet. (amended) 2. The tank of Claim 1 wherein said outlet is between 1 and 15° away from said axis. (amended) 3. The tank of Claim 2 wherein said outlet is between 5 and 10° away from said axis. (amended) -J• The tank of Claim 3 wherein said tank is for use as a liquid vessel in a space vehicle and the local gravitational vector is produced by spinning of the space vehicle. OMPI WIFO 5- The tank of Claim 1 wherein said tank is for use as a liquid vessel in a space vehicle and the local gravitational vector is produced by spinning of the space vehicle. (cancelled) 6. 7. The tank of Claim 5 wherein said tank is for use as a liquid vessel in a space ' vehicle and the local gravitational vector is produced by spinning of the space vehicle. 8. The tank of Claim 1 wherein said tank is for use as a liquid vessel in a space vehicle and the local gravitational vector is produced by spinning of the space vehicle. OMPI IPO

Inventors: SALVATORE JEREMIAH O
Applicants: HUGHES AIRCRAFT CO
Application year: 1981
Main classification: B64D37
IPC codes: B64D37, B64G1, B65D90