Patent Publication Number: US-2009238692-A1

Title: Blade of a turbo machine

Description:
The invention relates to a blade for a turbo machine. In the process all types of turbo machines come into consideration, for example turbines, pumps, drive rotors as components of marine engines. The blades of such machines serve the purpose of torque transmission. Either the forces of a streaming medium act on the blade, as for example in the case of a water turbine, or the blade exerts forces on the flowing medium, as for example in the case of ship propellers. 
     GB 1 345 835 describes a blade for a turbo machine. The blade is build of flexible walls and is inflatable. 
     GB 1 404 665 shows a blade for a gas turbine. The region of the blade that is flowed against is formed of a flexible wall which flows around a hollow space. A pressure medium can be introduced into the hollow space, so that the flexible wall deforms. 
     The shape of a blade is decisive for the efficiency of the torque transfer. The rotor blade is formed in such a way that it exhibits quite specific profile sections adapted to the operating conditions of the turbo machine. The operating conditions change, however, so that the selected profile section forms of the blades only constitute a compromise. The external flow of the individual blades is only optimal in the case of a specified operating state. If the parameters of such an operating state change—throughput, speed of the flowing medium etc.—this has a disadvantageous effect on the efficiency of the turbo machine as well as having a disadvantageous effect on the cavitation tendency. There are ship propellers which are equipped with symmetrically shaped propeller blades. Because of this a compromise for forward and backward motion is aimed at. This compromise is however not optimal, since efficiency losses of up to 25% arise, compared to a propeller whose blades are optimized for a specified direction of thrust. 
     There are controllable pitch propellers in which case the single blade can be swiveled around the longitudinal axis of the blade foot. This does bring a certain improvement. However, it is not possible to obtain the advantages of an optimized geometry of the blade with this. In addition, this is an expensive solution. 
     The invention is based on the object of designing a blade of a turbo machine in such a way that it works optimally to a great extent even in the case of different operating conditions. 
     This task is solved by means of a blade which exhibits the features of claim  1 . 
     Such blades have the property of automatically adapting the form of the concerned supporting surface of the blade to the respective operating conditions. This relates in particular to the curvature of the supporting surface. With this it is possible to optimize the power conversion increase the efficiency of the turbo machine. 
     The blade in accordance with the invention comprises hence an internal supporting structure and an elastic cover surrounding the supporting structure, said cover being in contact with fluid in the case of operation. The supporting structure exhibits a contour which corresponds to the contour of a conventional blade. The profile of the supporting structure is not necessarily optimized with regard to specified operating conditions. The profile can—with regard to the two lateral faces—be symmetrical and—in a cross-section vertical to the two lateral areas lateral faces—exhibit the shape of a lance point. 
     A flowable inflating medium is placed between the elastic cover and the supporting structure. This can be located on one side or on the other side. Depending on which side it is located on, the part of the elastic cover located there will be inflated and hence more greatly curved than on the other side. 
     Measures can be taken in order to facilitate an overflowing of the inflating medium from the one side of the blade to the other. Perforations in the supporting structure for example come into consideration as such measures. 
     In the case of the operation of the concerned hydraulic machine the inflating medium shifts to one of the two sides of the blade, so that the elastic cover alone is bulged on that side. This will always be the side of the blade which lies opposite the side that is flowed against. The bulging takes place therefore always on the “right” side of the blade, consequently where said bulging is desired for the purpose of optimization of the work of the hydraulic machine. 
     This is especially important for ship propellers whose direction of rotation is known to be reversible to change the direction of thrust. In the process the suction face and blade face of the blade are interchanged. 
     As an alternative to the described embodiment however the following comes into consideration: The two spaces on both sides of the supporting structure—between the supporting structure and the elastic cover—can be connected to a pressure medium. Hence the one or other space can be supplied pressure medium in variable measure; that is, with variable quantity and under variable pressure. 
     In this case the supporting structure does not need to be perforated. Rather it has the function of an inside wall. 
    
    
     
       The invention will be explained more closely with the help of the drawing. The drawing shows the following: 
         FIG. 1  shows in schematic representation and in a section the blade of a ship propeller in a first approach flow condition. 
         FIG. 2  shows the subject matter of  FIG. 1  in a second approach flow condition. 
     
    
    
     The blade  1  depicted in  FIG. 1  comprises a supporting structure  2 . Said structure has the contour of a lance point. It is shaped symmetrically with regard to its longitudinal axis. The two outer surfaces of the supporting structure  2  hence have the same course. 
     The supporting structure  2  is surrounded by an elastic cover  3 . Any type of material comes into consideration, for example rubber or plastic. The elastic cover  3  exhibits a certain oversize compared to the supporting structure  2 , so that a space arises on the one or the other side of the blade  1 . 
     Between the elastic cover  3  and the supporting structure  2  there is a flowable medium  4 , in the following named “inflating medium”. This can flow through perforations  2 . 1  in the supporting structure  2  from the one side of the blade to the other. The two  FIGS. 1 and 2  show the inflating medium  4  on different sides of the blade  1 . 
     As one furthermore recognizes from  FIGS. 1 and 2 , the inflating medium is on the side of the blade turned away from the approach flow side. Simultaneously one sees that the elastic cover  3  is more greatly bulged on the side where the inflating medium  4  is located. 
     In the case of operation this condition automatically ensues. If the direction of rotation of the ship propeller is reversed, because one would like to change the direction of thrust, the pressure distribution on the blade effects an excess pressure and because of this a bulge on the side, as shown in the figures. The bulge is located on the “right” side. A better external flow of the blade  1  arises. 
     The efficiency is increased and cavitation is prevented. 
     The invention is also applicable in the case of blades shaped otherwise. For example, blades can be used that are not shaped symmetrically, as cited above. It is also possible to use the invention in the case of blades whose form or contour can be changed by other measures. 
       FIG. 1  shows the blades  1  of the rotor of the first of two units. In the present case it is a matter of seven blades. However, there could also be more or fewer. As one sees, the free ends of the blades point to the center of the stream unit, so that a clearance remains between the free ends. 
     From  FIG. 2  one recognizes that it is a matter of two units. From here some of the blades of the two stream units can be recognized, namely again blades  1  of the first unit and blades of the second unit. 
     REFERENCE LIST 
     
         
           1  Blade 
           2  Supporting structure 
           2 . 1  Perforation 
           3  Elastic cover 
           4  Inflating medium