Self-actuating, foldable obstacle system on hydraulic lifting bodies

Abstract

A foldable obstacle system is provided on a hydraulic lifting body to alleviate cloud cavitation and so to reduce noise and surface erosion that might otherwise result from unsteady sheet cavitation and a re-entrant jet produced thereby. The system includes one or more foldable obstacle devices or plates, each of which is movable between a closed position at the surface of the body and an open position away from the body. When a re-entrant jet occurs, the jet acts to lift the plates and rotate them into the open position in which they block the re-entrant jet so as to reduce or prevent cloud cavitation. When cavitation does not occur, the normal fluid flow over the body acts to close and keep closed the obstacle devices or plates so that they do not interfere with the normal fluid flow.

What is claimed is:  
     
         1 . A foldable obstacle device for blocking a re-entrant jet produced by unsteady sheet cavitation on a hydraulic lifting body, the foldable obstacle device being mounted at a surface of the body and being movable between a closed position at the surface of the body and an open position away from the body, the foldable obstacle device being lifted from the closed position and moved into the open position by the occurrence of a re-entrant jet to block the re-entrant jet and reduce or prevent cloud cavitation.  
     
     
         2 . A foldable obstacle device according to  claim 1 , wherein the obstacle device is substantially perpendicular to the surface of the body when in the open position and is mounted so that it cannot be moved beyond the open position.  
     
     
         3 . A foldable obstacle device according to  claim 1 , wherein the obstacle device comprises a plate-like device which is pivotally mounted adjacent the surface of the body.  
     
     
         4 . A foldable obstacle device according to  claim 3 , wherein the plate-like device is pivotally mounted at a first edge thereof and has a plurality of feather-like flaps extending from a second edge thereof opposite the first edge.  
     
     
         5 . A hydraulic lifting body having a plurality of foldable obstacle devices according to  claim 1 , wherein the plurality of foldable obstacle devices being mounted at different locations on the surface of the body and each being movable between closed and open positions independently of other ones of the plurality of foldable obstacles.  
     
     
         6 . A hydraulic lifting body according to  claim 5 , wherein the plurality of foldable obstacle devices are mounted for pivoting movement along a common axis.  
     
     
         7 . A hydraulic lifting body having a plate-like obstacle device pivotally mounted adjacent a surface of the hydraulic lifting body so as to be movable between a closed position in which the device is generally continuous with the surface of the body and an open position in which the device extends outwardly from the surface of the body in response to a re-entrant jet at the surface of the body.  
     
     
         8 . A hydraulic lifting body according to  claim 7 , wherein the body has a chord length and a leading edge, and the obstacle device is located at a distance of 35-50% of the chord length from the leading edge of the body.  
     
     
         9 . A hydraulic lifting body according to  claim 8 , wherein the obstacle device is located at a distance of approximately 37% of the chord length from the leading edge of the body.  
     
     
         10 . A hydraulic lifting body according to  claim 7 , wherein the body has a chord length and the obstacle device extends upwardly from the surface of the body by a height which is at least 1.2-2.0% of the chord length.  
     
     
         11 . A hydraulic lifting body according to  claim 7 , wherein a sheet cavity of a certain thickness forms at the surface of the body when cloud cavitation occurs at the surface providing a re-entrant jet of a certain thickness at the surface of the body, and the obstacle device extends outwardly from the surface of the body and has a height which is greater than the thickness of the re-entrant jet and less than the thickness of the sheet cavity.,  
     
     
         12 . A hydraulic lifting body according to  claim 7 , wherein the obstacle device is pivotally mounted at a first edge thereof adjacent the surface of the lifting body and extends to an opposite second edge thereof so as to be generally continuous with the surface when in the closed position, and further including at least one feather-like flap extending from the second edge of the device so as to be generally continuous with the surface when in the closed position.  
     
     
         13 . A hydraulic lifting body according to  claim 12 , wherein each of the feather-like flaps is has a shape selected from the group consisting of rectangular, square, trapezoidal, semi-elliptic, semi-circular.  
     
     
         14 . A hydraulic lifting body according to  claim 7 , wherein the body has a plurality of the plate-like obstacle devices mounted adjacent a surface of the hydraulic lifting body and each being movable independently of the other obstacle devices.  
     
     
         15 . A hydraulic lifting body extending laterally between opposite leading and trailing edges and having opposite surfaces, the body comprising an elongated groove in a first one of the opposite surfaces extending laterally along a portion of the body at a location intermediate the opposite leading and trailing edges, a plurality of generally cylindrical hubs rotatably disposed, end-to-end, within the elongated groove and each having a shaft extending from a first end thereof and a hole at an opposite second end thereof for receiving the shaft of an adjacent hub, each of the hubs having one of a plurality of plates mounted thereon, rotation of each of the hubs within the elongated groove moving the plate mounted thereon between a closed position in which an external surface of the plate is generally continuous with the first one of the opposite surfaces of the body and an open position in which the plate is generally perpendicular to the first one of the opposite surfaces of the body.  
     
     
         16 . A hydraulic lifting body according to  claim 15 , wherein each shaft is rotatable within the hole of an adjacent hub in which it is received so that each plate may pivot between the closed and open positions thereof independent of the other plates.  
     
     
         17 . A hydraulic lifting body according to  claim 15 , wherein the groove provides a clearance fit of each of the hubs therein which prevents movement of the plates beyond the open positions thereof.  
     
     
         18 . A hydraulic lifting body according to  claim 15 , wherein each of the plates has at least one feather-like flap extending from an outer edge thereof opposite the hub on which the plate is mounted, the flap being generally continuous with the first one of the opposite surfaces of the body when the plate is in the closed position.  
     
     
         19 . A hydraulic lifting body according to  claim 15 , further including a pair of covers secured on the first one of the opposite surfaces of the body at opposite ends of the plurality of hubs to rotatably secure the plurality of hubs within the groove.  
     
     
         20 . A hydraulic lifting body which is subject to formation of a cloud cavity on a surface thereof if a re-entrant jet is produced, apparatus for minimizing or preventing formation of a cloud cavity comprising means responsive to production of a re-entrant jet for blocking the re-entrant jet from moving forward on the surface of the body, and means responsive to the absence of a re-entrant jet for allowing unblocked fluid flow over the surface of the body.  
     
     
         21 . A hydraulic lifting body in accordance with  claim 20 , wherein the body has a leading edge and an opposite trailing edge, fluid flow normally occurs over the surface of the body from the leading edge to the trailing edge, and a re-entrant jet, when produced, flows over the surface of the body from an end of an unsteady sheet cavity in a direction toward the leading edge.  
     
     
         22 . A movable obstacle for installation on a hydraulic lifting body, the foldable obstacle comprising: 
 a blocking plate portion;    a hub at one end of the blocking plate portion; and    mounting structure for mounting the hub to the lifting body so that the blocking plate portion is movable between a first position in which it is closed against the hydraulic lifting body and a second position in which it is opened away from the hydraulic lifting body;    wherein the hub is mounted to the mounting structure so that a re-entrant jet flowing over the lifting body applies a force to the movable obstacle and wherein the force of the re-entrant jet urges the blocking plate portion to its opened position.    
     
     
         23 . The movable obstacle of  claim 22 , wherein the blocking plate portion is substantially perpendicular to a surface of the lifting body when the blocking plate is in its opened position.  
     
     
         24 . The movable obstacle of  claim 22 , and further comprising at least one feather-like flap mounted on the blocking plate portion at an end opposite the hub.  
     
     
         25 . A hydraulic lifting body having at least one movable obstacle according to  claim 1  installed on the lifting body.  
     
     
         26 . The hydraulic lifting body of  claim 25 , wherein a plurality of the movable obstacles are installed on the lifting bodies.  
     
     
         27 . A fluid lifting body comprising: 
 a fluid lifting body surface; and    a movable obstacle comprising: 
 a blocking portion; and  
 mounting structure for mounting the movable obstacle on the lifting body so that the blocking plate portion is movable between a first position in which blocking plate portion is closed against the fluid lifting body surface and a second position in which the blocking plate portion is opened away from the fluid lifting body surface;  
   wherein the movable obstacle is mounted on the lifting body so that a re-entrant jet flowing over the lifting body applies a force to the movable obstacle;    wherein the force of the re-entrant jet urges the blocking plate to its opened position; and    wherein the blocking structure in the opened position interferes with the flow of the re-entrant jet over the lifting body surface.    
     
     
         28 . The fluid lifting body of  claim 27 , wherein the lifting body has a chord length and a leading edge, and wherein the movable obstacle is mounted on the lifting body at a distance of 35-50% of the chord length from the leading edge of the lifting body.  
     
     
         29 . The fluid lifting body of  claim 28 , wherein the movable obstacle is mounted on the lifting body at a distance of approximately 37% of the chord length from the leading edge of the lifting body.  
     
     
         30 . The fluid lifting body of  claim 27 , wherein the lifting body has a chord length, and wherein the movable obstacle in the opened position extends upward from the lifting body surface to a height of at least about 1.2% of the chord length.  
     
     
         31 . The fluid lifting body of  claim 30 , wherein the movable obstacle in the opened position extends upward from the lifting body surface to a height of between 1.2% and 2.0% of the chord length.  
     
     
         32 . The fluid lifting body of  claim 27 , wherein a sheet cavity having a sheet cavity thickness and a re-entrant jet having a re-entrant jet thickness form over the fluid lifting body surface under cloud cavitation conditions, and wherein the blocking portion extends outward from the fluid lifting body surface to a height that is greater than the re-entrant jet thickness and less than the sheet cavity thickness.  
     
     
         33 . The fluid lifting body of  claim 27 , wherein the movable obstacle is mounted at a first end thereof adjacent the fluid lifting body surface and extends to an opposite second thereof so as to be generally continuous with the fluid lifting body surface when the movable obstacle is in the closed position.  
     
     
         34 . The fluid lifting body of  claim 33 , and further comprising at least one feather-like flap extending from the second edge of the movable obstacle so as to be generally continuous with the fluid lifting body surface when the movable obstacle is in the closed position.  
     
     
         35 . The fluid lifting body of  claim 27 , wherein the fluid lifting body includes a plurality of the movable obstacles, and wherein the movable obstacles are movable independently of one another.  
     
     
         36 . A method for reducing fluid cavitation over a fluid lifting body, the method comprising: 
 flowing fluid over a flow surface of the lifting body, wherein flowing the fluid over the flow surface forms a re-entrant jet over the flow surface;    interposing a movable blocking structure into the re-entrant jet to interfere with flow of the re-entrant jet over the flow surface.    
     
     
         37 . The method of  claim 36 , wherein the lifting body has a chord length and a leading edge, and wherein the movable blocking structure is located at a distance of 35-50% of the chord length from the leading edge of the body.  
     
     
         38 . The method of  claim 37 , wherein the movable blocking structure is located at a distance of approximately 37% of the chord length from the leading edge of the body.  
     
     
         39 . The method of  claim 36 , wherein the lifting body has a chord length, and wherein interposing the movable blocking structure into the re-entrant jet includes extending the blocking structure away from the flow surface to a distance that is at least 1.2% of the chord length.  
     
     
         40 . The method of  claim 36 , wherein a sheet cavity having a sheet cavity thickness is formed over the flow surface; 
 wherein the re-entrant jet has a re-entrant jet thickness; and    wherein interposing the movable blocking structure into the re-entrant jet includes extending the blocking structure away from the flow surface to a distance between the re-entrant jet thickness and the sheet cavity thickness.    
     
     
         41 . The method of  claim 36 , wherein interposing the movable blocking structure into the re-entrant jet includes pivoting the movable blocking structure at a first edge that is toward a leading edge of the lifting body to extend a second edge that is toward a trailing edge of the lifting body away from the flow surface.  
     
     
         42 . The method of  claim 36 , wherein interposing the movable blocking structure into the re-entrant jet includes: 
 locating the movable blocking structure at a position in which the re-entrant jet is directed against a feather-like flap to apply a force to the feather-like flap that urges the movable blocking structure toward an opened position; and    interposing the blocking structure into the re-entrant jet in a configuration in which the re-entrant jet urges the blocking structure more fully toward the opened position.    
     
     
         43 . The method of  claim 36 , and further comprising positioning the movable blocking structure in a configuration in which the flowing fluid is directed against the movable blocking structure in a direction that urges the movable blocking structure to move from an opened position to a closed position.  
     
     
         44 . The method of  claim 36 , wherein interposing a movable blocking structure into the re-entrant jet includes interposing a plurality of movable blocking structures into the re-entrant jet, wherein the plurality of movable blocking structures are urged into the re-entrant jet by a force applied by the re-entrant jet; and 
 wherein the movable blocking structures are movable into the re-entrant jet independently of one another.