Abstract:
A Kort nozzle, in particular a Kort nozzle configured rotatable around the rudder axis of a ship, wherein at least one opening is provided in the wall of the Kort nozzle, so that the occurence of recirculations or of swirls is avoided or reduced even with an angular position with respect to a longitudinal axis of the ship and a globally uniform flow pattern is adjusted as far as possible.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a Kort nozzle, in particular a Kort nozzle which is configured rotatable about the rudder axis of a ship. 
         [0003]    2. Description of the Related Art 
         [0004]    A Kort nozzle is a conically tapered tube in which the propeller of a ship is placed. The tube also forms the wall of the Kort nozzle. Due to the taper of the tube to the stern of the ship, the Kort nozzles can transmit an additional thrust to the ship without the output having to be increased. Besides the propulsion improving properties of the Kort nozzle, pitching by rough sea is thus reduced so that by sea disturbance the loss of velocity can be reduced and the directional stability can be increased. Since the inherent resistance of the Kort nozzle increases approximatively quadratically as the speed of the ship increases, its advantages are effective in particular for slow ships which have a big propeller thrust (for example tugboats, fishing vehicles, etc.). 
         [0005]    Besides fixed Kort nozzles behind which normally a rudder is placed in flow direction for the control of the ship, there are so-called “Kort rudder nozzles” for which the Kort nozzle is rotatable about the rudder axis of the ship which is in vertical direction. For this purpose, bearings are normally provided on the upper and lower side of the Kort nozzle on the outside of its wall for the rotatable positioning. In contrast, the propeller is still fixed so that the Kort nozzle also rotates around the propeller. Frequently, the Kort nozzle is connected with the rudder post and positioned in the rudder heel. It is normally swivellable about a vertical axis of rotation or about the rudder axis by approximately 30° to 35° to both sides. Thus, the Kort nozzle is a combination of propulsion improving means and rudder since a rudder effect is achieved by the excursion of the propeller jet at an angle to the ship longitudinal axis. For excursed rudder nozzles, the stern of the ship is pushed by the jet reaction propulsion. 
         [0006]      FIG. 5  illustrates an embodiment of a Kort nozzle  200  positioned rotatable about the rudder axis of a ship with a fixed propeller placed therein as it is known from the prior art. The Kort nozzle  200  is placed around the fixed ship propeller  210  of a ship (not represented here). Here the Kort nozzle is pivoted under an angle a of approximately 30° about the ship longitudinal axis  220 . The arrow  221  represents the flow direction of the sea water or salt water. A fixed flap  230  is provided in flow direction behind the propeller on the Kort nozzle  200 , through which the flow properties of the Kort rudder nozzle are positively influenced. Due to a reduced wall thickness, the inlet area  201  (with respect to the direction of the flow passing through the Kort nozzle  200 ) is configured widened with respect to the remaining area of the Kort nozzle  200 . This means that the inner diameter of the inlet area is bigger than the inner diameter in the remaining area of the Kort nozzle  200 . The water flow through the Kort nozzle  200  is increased which in turn increases the propulsion efficiency of the Kort nozzle. 
         [0007]    Comprehensive calculations, tests and simulations of the applicant resulted in that, for certain twisting angles of a conventional Kort nozzle, swirls or recirculations of the flow form in the area directly behind the propeller. These recirculations or swirls have a disadvantageous effect on the power of the Kort nozzle. They develop in particular directly behind the propeller in the side area of the propeller to which the Kort nozzle is turned. Due to the recirculations the flow rate of the water flowing through is considerably reduced in this area so that the driving power of the Kort nozzle is reduced. Since the recirculations occur only in a locally limited side area and the flow runs substantially laminarly in the other areas as usual, considerable vibrations which can be transmitted to the hull of the ship and which have also a disadvantageous effect adjust. Reference is made hereunder to the  FIGS. 6   a  and  6   b  for illustrating this problem. 
         [0008]      FIG. 6   a  shows schematically the topview of a cut Kort nozzle  200  as it is known from the state of the art. The arrows in  FIGS. 6   a  and  6   b  constitute the course of the flow. The ship propeller  210  is drawn only schematically for reasons of clarity. For this Kort nozzle  200 , contrary to the Kort nozzle of  FIG. 5 , a movable or swivellable flap  231  is placed in flow direction behind the propeller  210 . The Kort nozzle  200  is swivelled with an angle of approximately 15° with respect to the ship longitudinal axis. The rear part of the wall  202   a  of the Kort nozzle  200  has been rotated against the flow direction, i.e. to the propeller  210 , while the opposed part of the wall  202   b  has been rotated with the flow direction accordingly. 
         [0009]    The lower part area of the Kort nozzle  200  which is marked in  FIG. 6   a  is depicted enlarged in  FIG. 6   b.  It can be recognized therein that, due to the angular position of the Kort nozzle  200  with respect to the propeller  210  or to the ship longitudinal axis  220 , a swirl or recirculation of the flow forms in the outer edge area in flow direction directly behind the propeller  210 . Due to this recirculation, the mean flow rate in the main flow direction  221  is reduced to a minimum in this local area. Measurements and simulations in this area showed that there is a mean flow rate of 0.2 to 2 m/s in the main flow direction  221 . Compared to this, the mean flow rate is situated within a range of 12 to 16 m/s in the area between the flap  231  and the wall area  202   b.    
         [0010]    The water which flows laminarly outside along the wall  202   a  flows around the rounded-off edge of the wall of the Kort nozzle end area  203  to the inside and hits there the flow produced by the propeller  210  which is directed in the main flow direction  221 . A part of the outer flow is directed to the inside against the main flow direction  221  and flows on the inner side of the wall  202  against the main flow direction  221  to the area behind the propeller  210  and from there back again through the propeller  210 . Thus, a local circulation or recirculation of the flow is formed and the mean flow rate in the main flow direction  221  in this area is around zero. Therefore, the disadvantages described above occur. 
       SUMMARY OF THE INVENTION 
       [0011]    Starting from the prior state described above, the object of this invention is to provide a Kort nozzle for which the occurence of recirculations or swirls is avoided or reduced even with an angular position with respect to the ship longitudinal axis and which has a uniform over-all flow pattern. 
         [0012]    In accordance with the present invention, at least one opening is provided in the wall of the Kort nozzle. 
         [0013]    In this context, with openings, basically any opening of any configuration in the wall of the Kort nozzle is to be considered. The opening extends through the whole wall and thus consists of an inner and of an outer opening area and a central area connecting these two areas. It is decisive that a flow connection is created for the sea water or the salt water from outside the Kort nozzle through the at least one opening into the inside of the Kort nozzle. 
         [0014]    The wall of the Kort nozzle is formed by the nozzle ring which envelops the stationary ship propeller. Basically the at least one opening can be provided at any location of the wall of the Kort nozzle. However, preferably it is provided in a lateral area of the Kort nozzle, either on the starboard side, or on the port side. It is decisive that the at least one opening is configured provided or placed in the wall in such a manner that, due to the at least one opening, sea water or salt water can flow from outside the Kort nozzle throughout this opening into the inside of the Kort nozzle in such a manner that the recirculations or swirls which develop at certain swivelling angles of the Kort nozzle are suppressed or considerably reduced. Tests of the applicant resulted in that, due to such openings, the thrust of the Kort nozzle has been increased in the side areas in which typically swirls or recirculations occur by up to 20%. Furthermore, the vibrations transmitted to the hull have been reduced. 
         [0015]    Due to the at least one opening, a laminar flow is thus introduced from outside to the critical side areas of the Kort nozzle in which the swirls typically occur at certain swivelling angles. This laminar flow avoids that a recirculation flow can be formed in the side areas against the main flow direction. The thrust and the working stability and thus the efficiency of the Kort nozzle are considerably improved herewith. 
         [0016]    In order to be able to suppress the occurence of swirls in any swivelling direction, it is appropriate to provide at least two openings in the wall of the Kort nozzle. Advantageously, both openings are placed substantially opposite each other. Appropriately, both openings are moreover to be placed respectively in a side area of the Kort nozzle since normally the strongest swirls develop there for conventional Kort nozzles. It is thus guaranteed that the risk of the occurence of swirls or recirculations is reduced for a swivelling to the starboard side as well as for a swivelling to the port side. 
         [0017]    With respect to the height of the Kort nozzle, according to a preferred embodiment of the invention, the at least one opening is disposed in a central area. This being, the central area ranges from one third of the height of the Kort nozzle to approximately two thirds of the Kort nozzle, preferably from two fifths to three fifths of the height of the Kort nozzle. It is thus achieved that the at least one opening is placed in an area in which the swirls typically occur. Thus, the laminar flow flowing through the at least one opening can develop an optimal effect and can suppress the swirl as much as possible. According to the invention, it is particularly preferred to provide a central arrangement of the at least one opening with respect to the height of the Kort nozzle. This being, the height of the Kort nozzle corresponds to its vertical extension when mounted, i.e. to the distance between the opposed wall areas of the Kort nozzle along its vertical axis or along the rudder axis. 
         [0018]    The central areas of the Kort nozzle extend in their longitudinal extension over the whole length of the Kort nozzle. There are thus two central areas which are placed opposite to each other. According to another preferred embodiment of the invention, at least two openings are disposed in at least one of these two central areas. Furthermore, these at least two openings are placed in longitudinal direction of the Kort nozzle the one behind the other and/or in vertical direction lying above one another. Depending on the configuration of the Kort nozzle and of the propeller as well as the respective swivelling angle, the result to be achieved can thus be optimized, namely the improvement of the thrust and of the quiet running of the Kort nozzle. For this embodiment too, at least two openings are respectively provided in both central areas, whereby the openings of both central areas are advantageously placed opposite to each other. 
         [0019]    With respect to the length of the Kort nozzle, i.e. the dimensions of the Kort nozzle, when the Kort nozzle is not swivelled about the ship longitudinal axis, according to another preferred embodiment, the at least one opening is disposed in an area from one third to two thirds of the length, preferably from two fifths to three fifths of the length, particularly preferably in the middle. The effect of the at least one opening can again be optimized by this measure too. 
         [0020]    For a swivellable Kort nozzle with a fixed ship propeller placed therein, it is furthermore preferred to configure the at least one opening in such a manner that it is placed, for a swivelling angle of 10°, 15° or 20°, with its inner opening area substantially adjacent to the propeller. It is thus guaranteed that, for the above mentioned typical swivelling angles, the laminar flow which comes out of the inner opening area of the at least one opening, flowing from the outside to the inside into the Kort nozzle, hits directly the swirl area. The laminar flow can thus directly act against the recirculation flow and the effect of the at least one opening is further improved. Should in some cases other swivelling angles, for example 25° or 30°, be employed, the arrangement of the at least one opening can naturally be adapted accordingly. 
         [0021]    For the further optimization of the effect of the at least one opening for the efficiency of the Kort nozzle, it is provided in a further preferred embodiment of the invention to configure the at least one opening as an oblong slit. Moreover, it is advantageous that the slitlike opening substantially extends in the vertical direction. It is thus achieved that a vertically orientated flow band flows into the Kort nozzle from the outside to the inside and thus positively influences the critical area in which normally swirls develop. Furthermore, such an opening can be produced relatively easily. 
         [0022]    Furthermore, it is preferred that the at least one opening extends obliquely from the outside to the inside with respect to the main flow direction through the wall. This means that the middle line of the openings is orientated with a predetermined angle to the main flow direction or to the longitudinal axis of the Kort nozzle. It is thus guaranteed that the outer laminar flow flows from the outside to the inside into the Kort nozzle and that no water flows from the inside to the outside through the at least one opening. 
         [0023]    It is preferred in particular to configure the at least one opening with respect to the longitudinal axis of the Kort nozzle with an angle of 10° to 60°, preferably 20° to 45°, particularly preferably 30° to 35°. The indications of angles refer to the angle between the longitudinal axis of the Kort nozzle and the middle line of the at least one opening which extends from the outside to the inside through the at least one opening. 
         [0024]    For a further preferred embodiment of the invention, it is provided that the at least one opening tapers from the outer side of the wall or from its outer opening area to its inner opening area on the inner side of the wall. The speed of the flow which flows from outside into the Kort nozzle can thus be increased so that the overall efficiency of the Kort nozzle and the risk of the occurence of turbulences or recirculations are further reduced. 
         [0025]    Alternatively, the at least one opening can be configured substantially constant over its whole extension. 
         [0026]    Appropriately, at least one of the admission edges and/or at least one of the discharge edges of the at least one opening is to be configured rounded-off. In the flow direction, each opening has, for example for a slitlike vertically orientated opening, two vertically orientated admission edges and two vertically orientated discharge edges. The admission through the opening into the Kort nozzle is thus improved in so far as the risk that unwished swirls can occur on the admission or discharge edges due to a breakaway of the flow is reduced. 
         [0027]    The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         [0028]    In the drawing: 
           [0029]      FIG. 1   a  is a schematic perspective view of a Kort nozzle with two opposite openings which are positioned swivellable on the hull of a ship; 
           [0030]      FIG. 1   b  is a schematic sectional view of a portion of the Kort nozzle of  FIG. 1   a;    
           [0031]      FIG. 2   a  is a schematic perspective view of a Kort nozzle swivellably positioned on a hull of a ship for which two openings situated in succession in a horizontal direction are placed in each central area; 
           [0032]      FIG. 2   b  is a schematic sectional view of the Kort nozzle of  FIG. 2   a;    
           [0033]      FIG. 3  is a schematic perspective view of a Kort nozzle swivellably positioned on the hull of a ship with respectively three openings situated in succession in a vertical direction in each central area; 
           [0034]      FIG. 4  is a schematic sectional top view of a portion of a Kort nozzle with an opening with flow lines. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0035]      FIG. 1   a  is a perspective view of a Kort nozzle  100  which is positioned swivellable on the hull  10  of a ship. The hull  10  of a ship is depicted only partially for reasons of clarity. The Kort nozzle is connected with the hull  10  by a bearing  12  and is rotatable about the rudder axis  11 . The rudder axis  11  corresponds to the vertical axis. The Kort nozzle  100  is furthermore connected with the hull in its lower area by a further bearing (not represented here). Considering the flow direction  13 , a movable or controllable flap  14  follows at the end of the Kort nozzle  100 . The Kort nozzle  100  comprises a ring-shaped configured wall  15  which is configured conically and which tapers in the flow direction  13 . An opening  16  is placed respectively in the central side areas  15   a,    15   b  of the wall  15  with respect to the height of the Kort nozzle. The openings  15  are placed substantially in the middle with respect to the height. The openings  16  extend obliquely from the outside to the inside, this being considered in the flow direction  13 . They consist in a slit extending substantially vertically which tapers from the outside to the inside. Thus, the openings  16  have an approximately shovel-type appearance since the outer opening area  16   a  is wider than the inner opening area  16   b  because of the taper of the opening  16 . The propeller is omitted in  FIG. 1   a  for reasons of clarity but is placed, when mounted, inside the Kort nozzle  100 . 
         [0036]      FIG. 1   b  shows a sectional view of a portion of the Kort nozzle  100  of  FIG. 1   a.  In particular, the wall of the Kort nozzle  100  of  FIG. 1   b  is cut in the area of an opening  16 . It can be recognized that the opening  16  extends in flow direction obliquely from the outside to the inside and that it tapers to the inside. Correspondingly, the outer opening area  16   a  is wider than the inner opening area  16   b.  Among the two horizontally extending admission edges  17   a,    17   b  of the opening  16 , the rear admission edge  17   a  is configured rounded-off while the front admission edge  17   b  is configured angular. In the same way, the rear discharge edge  18   a  is rounded-off in flow direction  13  while the front discharge edge  18   b  is angular. When considered from the side, the outer opening area  16   a  and the inner opening area  16   b  of the opening are offset to each other, in particular they are placed offset laterally to each other. Thus, the inner opening area  16   b  is covered by the obliquely extending side walls of the opening  16  or by the wall  15 , with respect to a side view of the Kort nozzle  100 . In other words, the opening is configured as a slitlike channel which extends obliquely from the outside to the inside in flow direction  13 . 
         [0037]      FIG. 2   a  shows a perspective view of a further embodiment of a Kort nozzle according to the invention  100 . It can be recognized in  FIG. 2   a  that the flap  14  is supported in the upper rudder bearing  12  as well as in a lower flap bearing on the Kort nozzle  100 . Furthermore, two openings  16  are respectively placed in the central areas  15   a,    15   b  of the wall  15 , openings which are situated one behind the other in a ship longitudinal direction, when the Kort nozzle is not deviated, or in the longitudinal direction of the Kort nozzle. It can be recognized in  FIG. 2   a  that only the outer opening area of the openings  16  can be seen from the outside and the inner opening area is covered. Correspondingly, the outer and the inner opening area of the opening  16  are placed one behind the other in flow direction  13 . 
         [0038]      FIG. 2   b  shows a sectional view of the Kort nozzle  100  of  FIG. 2   a.  It can be recognized that the openings  16  are placed respectively opposite each other in both central areas  15   a,    15   b  of the wall  15 . Moreover, these openings  16  extend obliquely from the outside to the inside in flow direction  13 . The single openings  16  are moulded respectively identical and thus extend parallel to each other. 
         [0039]      FIG. 3  shows a further embodiment of a Kort nozzle  100  according to the invention. For this embodiment, three openings  16  placed one above the other in a vertical direction are provided in each central area  15   a,    15   b  of the wall  15 . The openings  16  are placed respectively in the middle with respect to the longitudinal direction of the Kort nozzle  100 . The distance between the single openings  16  of a central area  15   a,    15   b  is respectively approximately the same. 
         [0040]      FIG. 4  shows a flow pattern of a side area of a Kort nozzle  100  with a portion of a schematically depicted propeller  20 . Overall, the depiction of  FIG. 4  is similar to that of  FIG. 6   b,  whereby contrary to the depiction of  FIG. 6   b  a Kort nozzle according to the invention with an opening  16  has been used. The represented arrows symbolize the flow course of the water flowing through the Kort nozzle. As it can be recognized, water flows from the outside to the inside through the opening  16 . As soon as it passes the inner opening area  16   b  of the opening  16  it flows further along the inner side of the wall  15  until it finally leaves the Kort nozzle  100 . Thus, no back circulation or swirl can form in the area between the outside of the propeller  20  and the end side of the Kort nozzle  100  with respect to the flow direction  13 . On the contrary, the whole flow flows laminarly inside the Kort nozzle  100  and also outside on the edge of the Kort nozzle  100 . 
         [0041]    While specific embodiments of the invention have been shown and described in detail to illustrate the inventive principles, it will be understood that the invention may be embodied otherwise without departing from such principle