Title of Invention  AN AXIAL FLOW IMPELLER WITH TWISTLESS OR SINGLE CURVATURE SHAPE VANES OR BLADES, PARTICULARLY, THOUGH NOT EXCLUSIVELY FOR AXIAL FLOW TURBOMACHINES 

Abstract  An axial flow impeller with twistless or single curvature shape vanes or blades comprises a hub rotatable on a central axis; a plurality of vanes spaced circumferentially on the hub, characterised in that the said vanes have a single or twistless curvature transverse to their length. A method of manufacture of the axial flow impeller comprises the steps of selection of design parameters, dividing flow area into desired number of stream passages; determining inlet vane angles for each stream cylinder using inlet velocity triangle; choosing two cylinders having different radii; determining the angles, namely, namely ө and Φ; developing the stream cylinder; and determining vane angles β ; fixing the inlet and outlet edges of the vane; tabulation of the results; and drawing the shape of the impeller vane or blade. 
Full Text  This invention relates to an axial flow impeller with twistless or single curvature shape vanes or blades, particularly, though not exclusively, for axial flow turbomachines. An axial flow impeller comprises a central hub rotatable on an axis and a plurality of vanes or blades spaced circumferentially on the hub. These vanes are, according to this invention, made twistless or single curvature. Axial flow impeller comprises of a hub rotatable on a central axis and plurality of vanes spaced circumferentially on the hub. These vanes are designed with a new design procedure/method, which leads to twistless or single curvature vanes. For a given speed and geometric parameters, an axial impeller having twistless vanes develops same head and discharge as that of the axial impeller having twisted vanes, designed with conventional axial impeller design methods. The geometric parameters are number of vanes, and ratio of hub diameter to tip diameter. The new design methodology has a potential which avoids using of five axis machine to machine high precision metal impeller's blade, and also avoids use of costlier injectionmoulding or other moulding method. The salient features of this invention are: The proposed axial flow impeller has: a central hub rotatable on an axis and plurality of blades extending from the hub periphery, each of the blades comprising a root portion adjacent to the hub terminating in the tip portion away from the hub. Each of the axial impeller blades has single curvature or twistless shape and being designed to perform same functionality as that of the axial impeller having twisted or double curvature shape vanes. Each of the axial impeller blades is designed with an unconventional design methodology, which produces twistless or single curvature shape vanes. For given speed and geometric parameters, axial impeller having twistless vanes develops same head and discharge as that of the axial impeller having twisted vanes, which is designed with conventional axial impeller design methods. The geometric parameters are number of vanes and ratio of hub diameter to tip diameter. Since each of the axial impeller blades has single curvature shape, the blade can be manufactured using a simple manufacturing method. The design methodology employed has a potential which avoids using of five axis machine to machine high precision metal impeller's blade, and also avoids use of costlier injectionmoulding or other moulding method. The blades thus designed can have either a constant thickness or varying thickness as desired by structural or other considerations. This type of blade with single curvature allows the incorporation of a sliding portion of the vane leading to a simple method of obtaining a different performance. With the advancement of technology, since the discovery of the first centrifugal turbomachine roughly two centuries ago, the development in the field of turbomachines has been tremendous. Various types of turbomachines have come up and now we have the turbomachines for several duties and also to handle all types of fluids. Among the rotodynamic machines, the radial flow impellers are normally used for higher heads at lower discharges. The necessity to have larger discharges at low heads lead to the development ot axial tlow impellers, the now in such impellers is in axial direction, i.e. parallel to the axis of impeller. They have open impeller fitted with vanes, which resemble ship propellers, and hence they are also known as propeller pumps. For the same discharge, the axial flow impellers have the smallest transverse dimensions as compared to other type of rotodynamic impellers. Higher shape number, high discharge, and low head characterize them. In recent years the axial flow impellers have become popular because of their higher efficiencies as compared to the radial flow impellers. Pumps of such types are mainly used for irrigation, drainage, sewage disposal, docks dewatering and oil circulation. Nowadays these impellers are becoming widely applied in medical applications like blood circulation, permanent artificial hearts etc. However, their drawbacks are 1) limited suction capacity 2) low; head 3) Steeply descending power and efficiency curves. They are not very economical at discharges varying appreciably from the design point. The axial flow impeller, according to this invention, comprises a hub rotatable on a central axis; a plurality of vanes spaced circumferentially on the hub, characterised in that the said vanes have a single or twistless curvature transverse to their length. The method of manufacture of the axial flow impeller according to this invention comprises the steps of selection of design parameters, dividing flow area into desired number of stream passages; determining inlet vane angles for each stream cylinder using inlet velocity triangle; choosing two cylinders having different radii; determining the angles, namely, namely 6 and developing the stream cylinder; and determining vane angles P; fixing the inlet and outlet edges of vane; tabulation of the results; and drawing shape of the impeller vane or blade. The present invention will be more easily understood with reference to the following drawings Fig.l: Axial flow impeller having twisted or double curvature shape vanes. Fig.2: Velocity triangles at inlet and outlet edges of vane. Fig.3: Development of stream cylinder. Fig.4: Axial flow impeller having twistless vanes. Fig.l shows meridional view of an axial flow impeller having twisted vanes with hubl. the stream cylinders A, B, C, D. and twisted vane 2. A1 A2, B1 B2, C1 C2, D1 D2 are inlet and outlet edges of the vane on particular stream cylinder. Fig.2 shows Velocity triangles at inlet and outlet edges of vane where in symbol "c" denotes absolute velocity, "w" denotes relative velocity, "u" denotes tangential velocity, "a" denotes flow angle and "p" denotes vane angle. Suffix "1" and "2" refers to inlet and outlet edges of vane respectively. Suffix "h" and "t" refers to hub and tip stream cylinder respectively. Fig.3 shows stream cylinder development where "e" denotes axial width of vane, "s" denotes stacking point, "L" denotes chord length of vane, "r" denotes radius of curvature of vane in the development, "O" is the centre of this radius and "pY'and "pY' denotes vane angles at inlet and outlet edges of vane respectively. Fig.4 shows an axial flow impeller with central hub 1 on which twistless or single curvature shape vanes 2, which are designed with new method, are fixed circumferentially. The basic elements of an axial flow turbomachine are impeller and diffuser. The axial flow impeller vanes are having double curvature i.e. vanes are twisted as shown in Fig.I. The reason for this twist is as follows: If the velocity of fluid before the vane (co) and vane contraction factor (0\) are assumed constant, the meridional velocity at inlet cm,  c0* 1 is also constant for all the points on the inlet edge of vane, i.e., from tip radius to hub radius. Since peripheral velocity V increases form hub to tip, the inlet vane angle p1 = tan1 (cml/u) decreases from hub to tip. While designing the impeller vane angles required at different stream cylinders, energy addition has to be kept constant. This will result in a variation in the deflection, (p2 Pi)? imposed on the fluid by the vane. This deflection will be decreasing from hub to tip. The velocity triangles for the axial flow impeller at hub and tip diameters, which shows the variation of deflection, (p2 Pi)? are as shown in the figure 2. Change of vane angles and hence deflection from hub to tip will lead to a blade with twist in conventional design methods, i.e., Onedimensional and Aerodynamic methods of design. Since the vane is having twist or double curvature shape, it is difficult to manufacture this type of impeller vanes. In order to overcome this problem, a new design method or procedure has been developed for getting twistless vanes. Such twistless vanes are expected to have lesser secondary flows and reduced separation leading to a better performance. This feature also enhances the cavitation performance of the turbomachine considerably when it handles a liquid. The different steps, in brief involved in new design methodology are as follows:  a) Choosing of design parameters. b) Dividing flow area into desired number of stream passages. c) Finding inlet vane angles for each stream cylinder using inlet velocity triangle. d) Choosing two cylinders having different radii. e) Finding the angles, namely 0 and f) Developing the stream cylinder and Finding vane angles (p). g) Fixing the inlet and outlet edges of vane, h) Tabulation of results. i) Drawing of impeller shape. Among the chosen cylinders, radius of one of the cylinders corresponds to the stream cylinder radius and another cylinder radius needs to be selected in some way /iteratively. These cylinders need to be intersected in some way and the angles, namely 0 and Where H Woo= Head developed by blade. Ci„ = Peripheral component of absolute velocity at inlet edge of vane. C2u = Peripheral component of absolute velocity at outlet edge of vane. U = Peripheral velocity. g = Acceleration due to gravity . During design it has been assumed that fluid approaches the vane axially and hence C1u becomes zero. For a given stream cylinder, peripheral velocity is constant at inlet edge and outlet edge of vane. Once the vane angles are found, the corresponding angles 0 and w need to be found. This total procedure needs to be implemented at each stream cylinder by keeping the radius of the cylinder, which is other than stream cylinder, constant. The so found angles 0, It will be appreciated that various other ways of carrying out the method proposed herein are possible without departing from the scope and ambit of this invention We Claim: 1. An axial flow impeller with twistless or single curvature shape vanes or blades comprising a hub rotatable on a central axis: a plurality of vanes spaced circumferentially on the hub, characterised in that the said vanes have a single or twistless curvature traasverse to their length. 2. An axial flow impeller with twistless or single curvature shape vanes or blades substantially as herein described and illustrated.. 3. A method of manufacture of the axial flow impeller as claimed in Claim 1 comprising the steps of selection of design parameters, dividing flow area into desired number of stream passages; determining inlet vane angles for each stream cylinder using inlet velocity triangle; choosing two cylinders having different radii; determining the angles, namely, namely 0 and O; developing the stream cylinder; and determining vane angles p; fixing the inlet and outlet edges of the vane; tabulation of the results; and drawing the shape of the impeller vane or blade. 4. A method of manufacture of axial flow impeller with twistless or single curvature shape vanes or blades substantially as herein described and illustrated. Dated this the 9th June 2006 INDIAN INSTITUTE OF TECHNOLOGY M.K.RAO ^^^^"^ KAMATH & KAMATH .APPLICANTS' ATTORNEY 

1289che2005 complete specification as granted.pdf
1289che2005correspondneceothers.pdf
1289che2005description(complete).pdf
1289che2005description(provisional).pdf
Patent Number  234955  

Indian Patent Application Number  1289/CHE/2005  
PG Journal Number  29/2009  
Publication Date  17Jul2009  
Grant Date  22Jun2009  
Date of Filing  14Sep2005  
Name of Patentee  INDIAN INSTITUTE OF TECHNOLOGY  
Applicant Address  IIT PO CHENNAI 600 036  
Inventors:


PCT International Classification Number  F01D11/08  
PCT International Application Number  N/A  
PCT International Filing date  
PCT Conventions:
