Abstract: In the area of the support struts and/or the aerodynamic fairings downstream of the stator vanes, the cross-section of the bypass duct of a turbofan engine is enlarged such that the pressure variations caused by the stagnation effect of the installations and reacting on the fan are reduced, enabling the fan to be operated with more efficiency and stability and finally the losses of the overall system and the fuel consumption to be reduced. The cross-sectional enlargement is accomplished by modifying the course of the wall in a limited area, actually by gradually enlarging the flow cross-section in the bypass duct in the axial and in the circumferential direction, with this enlargement being confined to the area around the leading edge of the support struts and/or the aerodynamic fairings.

Abstract: A bladed stator sector for a turbo-engine reduces the occurrence of thermally-induced stress cracks in stator blades by increasing the flexibility of the sectors by using one or more cutouts. The stator sector includes at least one stator blade between inner and outer platforms and at least one flange on one or more of the platforms. Each flange has a first end portion fixed to one of the platforms and a second end portion that is not fixed to either of the platforms. The one or more cutouts may be located on the flange and may be non-opening.

Abstract: A compression system is disclosed, comprising a first compressor having a first flowpath, a second compressor having a second flowpath located axially aft from the first compressor, and a transition duct capable of flowing an airfow from the first compressor to the second compressor, the transition duct having at least one plasma actuator mounted in the transition duct.

Abstract: An air-conditioner comprises, in an accommodating structure: an axial compressor powered by a built-in motor unit which circulates air, an axial flow-straightening stator to create a static pressure in excess of atmospheric pressure by transferring the air stream obtained in a static centrifugal compressor that creates a rotational flow with the air stream being routed through an axial flow-straightener/diffuser. The flow-straightener/diffuser is internally hollow to circulate ambient air and, externally, straightens the turbulent flow into an axial flow and relieves the pressure. A transfer valve is adapted to the flow-straightener/diffuser to selectively regulate the flow of hot air with the addition of ambient air. A vortex accelerates the air stream using a turbulence effect before it enters an expansion chamber that produces cold and directs the air stream into a final air control valve under the selected temperature conditions.

Abstract: One embodiment is an apparatus comprising a first rotational gas turbine engine component including first threads; a second rotational gas turbine engine component including second threads; the first threads and the second threads being mated; and the first rotational engine component being fastened to the second rotational engine component substantially only by the first threads and the second threads being mated. Other embodiments include unique apparatuses, systems, devices, and methods relating to gas turbine engine interconnection. Further exemplary embodiments, forms, objects, features, advantages, aspects, and benefits of the present invention are included in the following description, drawings, and claims.

Abstract: A serial fan includes a frame, a plurality of rotor vanes, a support connected to the frame through a plurality of connecting parts. The plurality of rotor vanes are arranged in series in the frame along an axial direction and the plurality of connecting parts are disposed therebetween to minimize space occupied by the serial fan in the axial direction, and effectively increase the blast pressure.

Abstract: A locking and fixing device for a heat shield element, which heat shield element can be arranged along a heat shield row axially directly next to at least one blade provided in a blade row and has, axially facing the blade, at least two projections of rib-like design which are spaced apart in the circular circumferential direction, are raised above a side wall section facing the blade and define a clear intermediate space which extends in the circular circumferential direction and into which a locking lug provided on the blade can be fitted. Further disclosed is at least one rib-like projection, on its side facing away from the clear intermediate space, providing an extension which extends in the circular circumferential direction, is connected to the projection and the side wall section and rises above the side wall section at most up to the rib height of the projection.

Abstract: A method is disclosed for assembling a multi-stage compressor or a multi-stage turbine for use in a gas-turbine engine. The method comprises the steps of assembling a rotor drum so as to comprise a plurality of rotor discs 17, 18, and then releasably connecting a plurality of static components 38 to the assembled rotor drum 19, thus forming an intermediate structure. The intermediate structure is then inserted within an outer casing 50, preferably by lowering the outer casing 50 over the intermediate structure, whereafter the static components 38 are fixed to the outer casing 50. The static components 38 are then released from their connection to the rotor drum 19 in order to permit rotation of the drum 19 relative to the static components 38 and the outer casing 50.

Abstract: Blower made up of at least two axially stacked, interlocking fans. Each fan is enclosed in a housing the axially opposite ends of which are flanged. Opposing flats on immediately neighboring flanges are formed with complementary twist-locking features. The twist-locking features are configured in such a way that when the fans are stacked, the opposing flats will not be in contact with each other unless the housings are twisted out of axial alignment to bring the opposing flats flush together, and such that with the opposing flats flush in contact, twisting the housings back into axial alignment locks them together.

Abstract: A multistage pump assembly includes a manifold having an inlet port configured to be coupled to a supply pipe and an outlet port configured to be coupled to a discharge pipe. The inlet and outlet ports define an end suction, radial outlet port configuration. The pump assembly also includes a cartridge having a sleeve and plurality of pumping stages that define a pump stack received within the sleeve. An outer chamber is defined between the pump stack and the sleeve. Each of the pumping stages includes an impeller mounted along a pump shaft that rotates about a rotation axis. The cartridge is aligned horizontally such that the rotation axis is substantially horizontal. An end plate is positioned between the manifold and the cartridge and includes at least one cartridge engagement surface supporting the cartridge. The end plate is removably coupled to the manifold.

Abstract: A turbo pneumatic cylinder of a pneumatic tool, including a front turbine, a one-way rotatable inverse turbine and a rear turbine. The front and rear turbines are mounted on the rotary shaft of the pneumatic cylinder. The inverse turbine is one-way rotatably fitted on the rotary shaft between the front and rear turbines. Multiple blades are arranged on the circumferences of the front and rear turbine and the inverse turbines. The blades of the inverse turbine are directed in a direction reverse to the direction of the blades of the front and rear turbines. The front and rear turbines and the rotary shaft rotate in the same direction, while the inverse turbine rotates in a direction reverse to the direction of the front and rear turbines. As a result, the efficiency of the pneumatic cylinder is enhanced and the twisting of the pneumatic cylinder is avoided when it is in operation.

Abstract: Disclosed herein is a rotor assembly for a steam turbine. The steam turbine includes a retention portion having a stacked rotor section. The steam turbine further includes a first shaft end disposed at a first end of the retention portion. The steam turbine yet further includes a second shaft end disposed at a second end of the retention portion that is opposite to the first end of the retention portion.

Abstract: A blower unit has a first axial fan and a second axial fan for generating a flow of cooling air passing through a heat exchanger disposed under an intake duct through which an intake air to be introduced to an engine flows. The first axial fan and the second axial fan are aligned in a substantially horizontal direction downstream of the heat exchanger with respect to the flow of air. A first rotation axis of the first axial fan and a second rotation axis of the second axial fan are perpendicular to the heat exchanger and located lower than a center of the heat exchanger. The first axial fan, which is disposed on a right side of the second axial fan, rotates in a clockwise direction and the second axial fan rotates in a counterclockwise direction when viewed from a downstream position with respect to the flow of air.

Abstract: A counter-rotating axial-flow fan includes a housing that is constituted from a first divided housing unit and a second divided housing unit. Engaging members and first stopper portions are integrally formed with a first flange portion of the first divided housing unit. The first stopper portions are arranged adjacent to the engaging members. Engaged members and second stopper portions are integrally formed with a second flange portion of the second divided housing unit. The second stopper portions are arranged adjacent to the engaged members. The second stopper portions have leading ends that are abutted onto leading ends of the first stopper portions when the engaging members are completely engaged with the engaged members. Thus, damage of the first and second divided housing units is prevented when the first and second divided housing units are coupled.

Abstract: A method for modifying a multistage compressor (101) involves exchanging the rotor blades of the first compressor rotor blade row (LA1) for modified rotor blades which have an identical blade leaf profile (121) to the original rotor blades and the blade angle (B?11) of which is different from the blade angle (B?10) of the original rotor blades. Furthermore, the blades of at least one further blade row (LAN, LEN) arranged downstream of the second compressor stage are exchanged for modified blades which have an identical blade leaf profile (125, 126) to the original blades and the blade angle (B?N1, B?N1) of which is different from the blade angle (B?NO, B?NO) of the original blades. The method makes it possible to increase the mass flow of a compressor and essentially maintain the stability reserve against stall.

Abstract: Method and apparatus for pumping drilling fluid (mud) containing drill cuttings, comprising a centrifugal pump with screw pump accelerator. The screw pump creating positive pressure for centrifugal pump inlet to increase performance. The screw pump mud level fluctuations are compensated by the vertical screw pumping unit. Adjusting the elevation of pump will adjust the quantity of mud pumping, which is not possible with ether one pump alone. Air is allowed to mix with the mud in the centrifugal pump to create air bubbles to decrease density of the mixture and decrease the head pressure.

Abstract: A rotor comprising several blades rotating together with the rotor, particularly running blades, and the blades forming at least one blade ring, is disclosed. The blades within the, or each, blade ring are arranged at a different distance from one another.

Abstract: An axial turbine has a turbine stage including stator blades fixedly provided on a stationary section and moving blades fixedly provided on a rotating section and has a structure in which a flow blowing out from a space formed between the stator blades and the moving blades exists. In order to prevent a decrease in stage output power due to such blowout flow thereby to improve the turbine stage efficiency, the axial turbine comprises a member coupling an inner circumferential side of the stator blades, and a structure provided on a surface of the member opposed to the moving blades for bending a flow blowing out from the side of the rotating section into a space between the stator blades and the moving blades in a rotational direction of the rotating section.

Abstract: A cooling fan without returning flow comprises a motor stator, a frame and a motor rotor. The frame is joined to the stator with a support device at the inlet side thereof. The motor rotor is disposed at the stator. A fan blade set is disposed under the rotor and at the outlet side of the frame. An airflow area of the outlet can be increased to prevent the outlet side from producing a stagnation zone so as to increase cooling area and reduce noise.

Abstract: A turbine assembly includes a turbine having a seat extending outward from a top face and a bottom face of the turbine, a shaft hole defined in a bottom face of the seat, multiple blades divergently extending outward and multiple tapered passages each defined between two adjacent blades. A shaft is securely mounted on top of the seat and has an upper portion configured to allow the upper portion of the shaft to be snugly extended into the shaft hole of an adjacent turbine so that each turbine assembly is able to combine a different turbine assembly via the extension of the upper portion of the shaft into the shaft hole of the adjacent turbine.

Abstract: A serial fan includes a frame, a plurality of rotor vanes, at least one motor for driving the rotor vanes and a support connected to the frame through a plurality of connecting parts for receiving the at least one motor. The plurality of rotor vanes are arranged in series in the frame along an axial direction and the plurality of connecting parts are disposed therebetween to minimize space occupied by the serial fan in the axial direction, and effectively increase the blast pressure.

Abstract: A turbine is disclosed which includes a turbine blade housing having an inner facing portion of a first material having a first coefficient of expansion, and a turbine blade body having an outer facing portion of a second coefficient of expansion greater than said first coefficient. In a preferred embodiment, the blade housing comprises a number of steel shroud rings and the turbine blade body comprises a number of stators and rotors of a thermoplastic material. An interference fit between stator blades and the shroud rings is enhanced in use due to the difference in thermal and/or hydrophilic coefficients of expansion of the first and second materials.

Abstract: A radial-flow heat-dissipating fan includes a casing and a cover mounted to a side of the casing. The casing includes a compartment and a side air outlet, and the cover includes an air inlet. A primary fan wheel is rotatably mounted in the compartment and the primary fan wheel includes a hub and a plurality of radial-flow blades surrounding the hub. An auxiliary fan wheel is mounted in the air inlet of the cover and includes a plurality of axial-flow blades. An airflow transition area is defined between a circumference of the hub of the primary fan wheel, the radial-flow blades, and the axial-flow blades. The axial-flow blades increase axial inlet airflow via the air inlet, with the airflow transition area changing a direction of the axial inlet airflow into centrifugal airflow that is outputted via the side air outlet by the radial-flow blades.

Abstract: This specification discloses a serial fan comprising a plurality of rotor vanes, one or more supports and a frame. Each of the rotor vanes comprises an inlet, an outlet, and one or more blades. Each support supports at least one of the rotor vanes so that the corresponding rotor vane can rotate thereon. The frame connects all the supports. The rotor vanes are connected in series in the axial direction, and the design of each of the rotor vanes is such that the velocity vector of the air relative to one of the blades on the outlet side of the ith rotor vane plus the velocity vector of the blade of the (i+1)th rotor vane relative to that of the ith rotor vane gives the incoming velocity vector of the air relative to the (i+1)th rotor vane. This vector is essentially parallel to the extension direction of the blade on the inlet side of the (i+1)th rotor vane. Here, i is a natural number smaller than the number of the plurality of rotor vanes.

Abstract: A steam turbine 1 constructed in accordance with the present invention comprises a high-pressure module 2 and a low-pressure module 3, a speed-reducing gearbox 4, and an alternator, and wherein the high-pressure module 2 has a single stage of blades 20. This single stage of blades 20 performs the same function as a multi-stage high-pressure module, but with a blade design that is different from the blade design of multi-stage steam turbines. For example, the pressure ratio between the inlet and the outlet of the high-pressure module 2 may be in the range 3 to 20.

Abstract: A modular waterbrake that can be used with differing types and sizes of rotating machines includes common end stages, and a plurality of common intervening power stages. Each power stage will extract a certain amount of shaft horsepower from the machine under test, and each stage operates independently of one another. Thus, the modular water dynamometer can be used to zero in on desired torque test loads during machine testing, by simply activating or deactivating selected stages.

Abstract: A method for assembling a power system is provided. The method includes coupling a first turbine and second turbine together with a coupling that extends between a first rotor of a first turbine and a second rotor of the second turbine, and such that the first turbine has fluid flow along a first flow path, and the second turbine has fluid flow along a second flow path. The method further includes fixedly coupling an outer wall to the first turbine that directs fluid flow from the first flow path towards the second flow path.

Abstract: A fluid-flow machine includes an outer casing having a rotationally mounted rotor with three blade regions. The blade regions are divided into an inner blade region and two outer blade regions, the two outer blade regions pointing outward toward the outer casing end. The fluid-flow machine includes one or more outlet openings, via which the flow medium is divided into two partial flows. The two partial flows then flow through the respective outer blade regions.

Abstract: The invention is directed to a thick stator vane that effects continuous acceleration of the water stream within the jet pump, a non-uniform spacing of stator vanes or impeller blades to reduce noise output of the jet pump during operation, and a coupling structure positioned between the impeller and engine that prevents transfer of axial thrust to the engine caused by jet pump failure.

Abstract: A method for assembling a power system is provided. The method includes coupling a first turbine and second turbine together with a coupling that extends between a first rotor of a first turbine and a second rotor of the second turbine, and such that the first turbine has fluid flow along a first flow path, and the second turbine has fluid flow along a second flow path. The method further includes fixedly coupling an outer wall to the first turbine that directs fluid flow from the first flow path towards the second flow path.

Abstract: Electronic system components are cooled using a field configurable pump comprising a selectable plurality of identical or nearly identical modular pump units. The pump units are disposed in a stacked arrangement and are fluidly connected to adjacent modular pump units via a removable coupling, preferably one of the quick-disconnect variety. Each modular pump unit comprises a housing, an impeller and a sealing mechanism. When disposed in a stack the combined pump structure is driven by a single motor. In this fashion, pump structures may be employed which are adaptable to heat flux demands imposed by the electronic components.

Abstract: A fluid moving system is disclosed wherein a plurality of stacked blowers may provide for the redundant supply of cooling fluid such as air. This system may be advantageously utilized to cool electronic equipment or other uses. One or more of the blowers may utilize an impellor design that allows for the axial flow of fluid through the blower in addition to a transverse fluid outlet. In addition, the blowers may incorporate a flow gate operative to reduce back flow should a particular blower have a reduced fluid flow.

Abstract: The shafts of upstream and downstream turbines are interconnected by a coupling. A diffuser is provided in an intermediate cavity between the upstream and downstream turbines to recover kinetic energy, as well as minimize or eliminate windage and spinning losses resultant from exposure of the coupling to the flowpath along the turbines. A radial entry inlet provides a supplemental fluid admission into the intermediate cavity, the admission being turned axially and circumferentially for joining with the flow exiting the upstream turbine for combined flow to the downstream turbine.

Abstract: A fan (22) for a turbofan gas turbine engine (10) comprises a fan rotor (24) carrying a first set of circumferentially spaced radially extending fan blades (28) and a second set of circumferentially spaced radially extending fan blades (30). The second set of fan blades (30) is arranged downstream of the first set of fan blades (28). The hub to tip ratio (R1/R2) of the first set of fan blades (28) is substantially the same as the hub to tip ratio (R3/R4) of the second set of fan blades (30) and the radius (R2) of the radially outer ends of the first set of fan blades (28) is less than the radius (R4) of the radially outer ends of the second set of fan blades (30). This increases the flow area of the fan (22) by about 7% compared to a conventional fan of the same radius and thus increases the mass flow by about 7% and/or increases the pressure ratio.

Abstract: Disclosed is a backup heat-dissipating system having a serial fan which can be assembled easily, fastly and conveniently, and can effectively eliminate the interference between fans and prevent the air leakage resulting from the failed fan unit. The backup heat-dissipating system includes a main frame, a first rotor device disposed in the main frame and including a first control device, and a second rotor device disposed in the main frame to be coupled with the first rotor device in series along an axial direction of the main frame and including a second control device. When the first rotor device fails, the first control device will output a signal to the second control device for driving the second rotor device to rotate at a relatively higher speed.

Abstract: A fluid-flow machine includes an outer casing having a rotationally mounted rotor with three blade regions. The blade regions are divided into an inner blade region and two outer blade regions, the two outer blade regions pointing outward toward the outer casing end. The fluid-flow machine includes one or more outlet openings, via which the flow medium is divided into two partial flows. The two partial flows then flow through the respective outer blade regions.

Abstract: This specification discloses a serial fan comprising a plurality of rotor vanes, one or more supports and a frame. Each of the rotor vanes comprises an inlet, an outlet, and one or more blades. Each support supports at least one of the rotor vanes so that the corresponding rotor vane can rotate thereon. The frame connects all the supports. The rotor vanes are connected in series in the axial direction, and the design of each of the rotor vanes is such that the velocity vector of the air relative to one of the blades on the outlet side of the ith rotor vane plus the velocity vector of the blade of the (i+1)th rotor vane relative to that of the ith rotor vane gives the incoming velocity vector of the air relative to the (i+1)th rotor vane. This vector is essentially parallel to the extension direction of the blade on the inlet side of the (i+1)th rotor vane. Here, i is a natural number smaller than the number of the plurality of rotor vanes.

Abstract: An electrical non-priming submersible pump including a motor assembly that has a motor coupled to a shaft. The shaft has impellers formed thereon for propelling water. Also included is a housing assembly that surrounds the motor assembly. The housing assembly has an intake area that includes a multilayer sediment protection system that prevents the introduction of debris into the housing. The multi-layer sediments protection system includes a first plurality of slots positioned around the circumference of the housing assembly and a screen position in juxtaposition in relation to the first plurality of slots. A sprinkling system is also disclosed including an electrical non-priming submersible pump that is connected to a control panel which is connected to a header pipe section. The header pipe section is connected to a zone pipe section that includes sprinkler heads for applying water to a desired location.

Abstract: A fan (22) for a turbofan gas turbine engine (10) comprises a fan rotor (24) carrying a first set of circumferentially spaced radially extending fan blades (28) and a second set of circumferentially spaced radially extending fan blades (30). The second set of fan blades (30) is arranged downstream of the first set of fan blades (28). The hub to tip ratio (R1/R2) of the first set of fan blades (28) is substantially the same as the hub to tip ratio (R3/R4) of the second set of fan blades (30) and the radius (R2) of the radially outer ends of the first set of fan blades (28) is less than the radius (R4) of the radially outer ends of the second set of fan blades (30). This increases the flow area of the fan (22) by about 7% compared to a conventional fan of the same radius and thus increases the mass flow by about 7% and/or increases the pressure ratio.

Abstract: A technique for facilitating the movement of multi-phase fluids. The technique utilizes a compressor pump and a production pump. The compressor pump compresses a fluid to remove vapor phase and then discharges the pressurized fluid to a production pump. The production pump produces the pressurized fluid to a desired location with greater efficiency due to reduction of the vapor phase.

Abstract: A radial turbine blade system comprised of airfoils forming a circular array on a disk or series of disks around a central opening which serves as the exhaust outlet. Single or multiple sections comprised of a circular array of airfoils on a disk are arranged along the central axis. Nozzles direct high velocity mass flow fluids between the disks and onto the leading edges the airfoils. Three forces are used to convert the high velocity mass flow to mechanical output. First, is the shock effect of high velocity particles striking the leading surface of the airfoils. Second, is the lift force vector produced by the fluid flow over the airfoils. Third, is the fluid motive force of the high velocity mass flow contacting the inner walls of the disks. The invention can utilize various types of fluid forces such as gasses produced from the combustion of fuel or steam.

Abstract: A steam turbine rotor having a combination of at least one of a high pressure rotor, an intermediate pressure rotor and a low pressure rotor, which are each formed from a metal material of different chemical composition and welded together by means of welding.

Abstract: A cell for pumping a multiphase effluent includes two rotary parts (4-5), the first one (4) having a hydraulic wheel designed for transmitting kinetic energy to each of the multiphase effluent phases entering cell (1a-1b), and the second one (5), following the first, being an energy converting device designed for homogenizing the phases, transferring kinetic energy between the phases, entraining the lightest phase, converting kinetic energy into pressure and compressing the homogeneous effluent before it leaves the cell. All of the rotary parts of the cell are mounted on a common shaft (3) axially arranged inside a fixed housing (2) having an inlet and an outlet for the multiphase effluent.

Abstract: A rotor assembly for a gas turbine engine operates with reduced circumferential rim stress. The rotor assembly includes a rotor including a plurality of rotor blades extending radially outward from an annular rim. A root fillet extends circumferentially around each blade between the blades and rim. The rim includes an outer surface including a plurality of concave indentations extending between adjacent rotor blades and forming a compound radius. Each indentation extends from a leading edge of the rotor blades towards a trailing edge of the rotor blades.

Abstract: In an impeller of an axial-flow blower driven by an outer rotor type motor, the impeller is formed in sections so that individual impeller sections 5F and 5R can easily be formed by molding with an axial coupling type die, and also which are arranged in series to construct the entire impeller, thereby realizing an impeller structure in which adjacent impeller blades overlap each other. The number of impeller blades of the front section impeller is more than that of the rear section impeller to reduce the noise generated during the rotation of the impeller.

Abstract: A compact turbo-molecular pump has a relatively short axial length and yet provides sufficient evacuation and compression capabilities. The turbo-molecular pump comprises a casing (10) which contains an exhaust vane section (L1) having rotary vanes (30) on a rotor section alternating with stationary vanes (32) on a stator section. The exhaust vane section comprises an axial exhaust vane section (L1) and a radial exhaust vane section (L2) disposed downstream of the axial exhaust vane section (L1).

Abstract: A multi-stage propeller assembly including a barrel having a cylindrical actuation part and a tapered nozzle part, with the tapered nozzle part integrally extending from the cylindrical actuation part while being reduced in its diameter in a direction from one end around the actuation part to the other end. A drive engine for propellers is installed within the tapered nozzle part, with the drive shaft of the engine axially extending within the actuation part. A plurality of propellers are regularly set along the drive shaft to form the multi-stage propeller assembly. A plurality of fixed radial blade units are regularly set between the propellers.

Abstract: It is an object of the present invention to provide a stator blade for an axial-flow compressor, in which the wave drag due to the generation of a shock wave in a transonic speed range can be suppressed to the minimum. For this purpose, the stator blade in the axial-flow compressor has an intrados producing a positive pressure, and an extrados producing a negative pressure. Both of the intrados and the extrados are located on one side of a chord line. A first bulge and a second bulge are formed on the intrados of the stator blade at a location on the side of a leading edge and on the side of a trailing edge, respectively. Thus, the generation of a shock wave on the extrados can be moderated to reduce the wave drag by positively producing the separation of a boundary layer on the intrados by the first bulge.

Abstract: An air turbine motor has a turbine wheel mounted for rotation in a housing. A first set of elements distributed around the circumference of the turbine wheel drive the wheel in rotation in response to an axial flow of drive air. A second set of elements on a face of the wheel drive the wheel in rotation in response to radial flow of drive air. Stators direct drive air to the first elements in an axial direction and to the second elements in a radial direction.

Abstract: A fan guard has a function of supercharging a fan in addition to supporting a rotor device is disclosed. The fan guard is to be mounted beside the rotor device for supporting the rotor device, and additionally, the fan guard interacts with an airflow generated by the revolution of the rotor blades to supercharge the fan. The fan guard essentially includes a main frame, and a set of guard blades radially arranged inside the main frame and fixed onto an inner surface of the main frame by each one end thereof. Each of the guard blades is preferred to have a shape similar to the shape of the rotor blades, and the set of guard blades can be arranged either upstream or downstream of the rotor blades.