47results about How to "Improve aerodynamic efficiency" patented technology

The invention discloses a ducted unmanned aerial vehicle structure. The device comprises a machine body supporting beam, fixed ducted fans and movable ducted fans are arranged on the left side and the right side of the machine body supporting beam, the fixed ducted fans are arranged on the front side and the rear side of the movable ducted fans, a fixed frame and a telescopic frame are arranged on the machine body supporting beam, and the fixed ducted fans and the machine body supporting beam are fixed. The movable ducted fan and the machine body supporting beam are movably connected left and right, the fixed ducted fan and the movable ducted fan each comprise a ducted body, a motor base is arranged on the inner side of each ducted body, the motor bases and the ducted bodies are fixed through a plurality of guide vanes, motors are fixed to the motor bases, water cooling cavities are formed in the motor bases, and the water cooling cavities are formed in the outer sides of the motors. A cooling water channel is arranged on the inner side of the guide vane. The folding unmanned aerial vehicle has the beneficial effects that the folded unmanned aerial vehicle is of an H-shaped structure, and the trafficability of road transportation or road driving can be met; and the extended unmanned aerial vehicle is of a *-shaped structure, so that the yaw control capability is improved.

The utility model provides a wind resistance balancing wing plate, which belongs to the technical field of balancing wing plates, and comprises a wing plate main body, the wing plate main body is divided into a front edge, a wing-shaped middle part and a rear edge along the spanwise direction, the wing plate main body is provided with a sawtooth structure, the sawtooth structure is continuously arranged triangular sawteeth, and the triangular sawteeth are arranged in the wing plate main body. The sawtooth structures are integrated on the edge of the wing plate body to form an integrated structure, the vertex of each sawtooth is located on the edge line of the wing plate body, gears of the sawtooth structures are arranged in a staggered mode, and the sawtooth structures are continuously distributed along at least one side edge of the wing plate body. The sawtooth structures are continuously distributed along the edge of at least one side of the wing plate body, preferably distributed on the edges of the two sides, so that the airflow optimization effect is maximized, turbulent flow of a traditional wind resistance balance wing plate is reduced, the smoothness of airflow is improved, and therefore wind resistance is reduced, and stability and efficiency are enhanced.

The invention aims to provide an aircraft propulsion system which comprises an energy storage unit and a tail fan assembly, the energy storage unit is arranged in an aircraft body, the tail fan assembly is arranged at the tail of an aircraft, and the tail fan assembly comprises a first driving unit, a tail fan rotor and a tail fan stator. The first driving unit is electrically connected with the energy storage unit, the tail fan rotor is arranged on the periphery of the tail of the aircraft and is in transmission connection with the first driving unit, and the tail fan stator is arranged on the periphery of the tail of the aircraft. The tail fan stator is closer to the rear end of the aircraft than the tail fan rotor. By adopting the aircraft propulsion system, the propulsion efficiency of the existing aircraft can be improved, and the fuel consumption of the aircraft in the whole voyage can be reduced.

The invention provides a supersonic-speed jet adopting supersonic-speed double wings and variant design, and belongs to the field of novel supersonic-speed civil aircrafts, a large-area truncated delta wing with edgings on the inner side is adopted, an engine nacelle is arranged on the upper portion of the outer end of the large-area truncated delta wing, and the supersonic-speed double wings are installed on the outer side of the nacelle; the front edges and the rear edges of the upper wing and the lower wing of the supersonic double-wing adopt intelligent materials to realize a variant function; the empennage can rotate around a mounting shaft in the longitudinal direction of the airplane to change the inclination angle; the front edge and the rear edge of the supersonic double-wing are deformed, and the inclination angle of the empennage is changed to jointly form a supersonic state and a subsonic state. The problem that the conventional double-wing non-design-point performance is poor is solved, high aerodynamic performance can be achieved within the flight envelope range, and it is guaranteed that an aircraft achieves ideal supersonic speed environment-friendly performance such as acoustic explosion and noise and aerodynamic efficiency.

The utility model discloses a turbofan shell, centrifugal turbofan and breathing machine, wherein the turbofan shell comprises a volute upper cover, a volute lower cover fixedly installed below the volute upper cover, an air flow channel forming circumferential uniform section and an air outlet communicated with the air flow channel, the air outlet is tangent to the air flow channel, and the centrifugal turbofan is arranged in the volute lower cover. An air inlet is formed in the top of the volute upper cover, a filling block which is installed on the volute upper cover and is of a spiral structure is arranged in the airflow channel, the starting end of the filling block is located at a circumferential inlet of the airflow channel, and the tail end of the filling block right faces the air outlet. And the thickness of the filling block is linearly reduced to zero from the starting end along with the increase of the circumferential angle of the airflow channel. According to the utility model, the filling block with the spiral structure is arranged, and the thickness of the filling block is gradually reduced, so that the runner area of the airflow channel is gradually increased along with the increase of the circumferential angle in the circumferential direction, the flow change of airflow is better met, the pneumatic efficiency is improved, and the noise is reduced.

The invention relates to a sealing structure, a sealing method, a gas compressor and a gas turbine engine. The sealing structure comprises a first part and a second part, wherein the first part is located at the root of the stator blade; the second part is positioned on the rotor corresponding to the stator blade; a sealing gap is formed between the first part and the second part in the radial direction; wherein the first part comprises a honeycomb body and a protruding body, the second part comprises a first tooth and a second tooth which are adjacent in the axial direction, and the second tooth is located on the downstream of the first tooth; the axial positions of the first teeth and the second teeth correspond to the axial position of the honeycomb body, the axial position of the protruding body corresponds to a first axial area between the first teeth and the second teeth, and the protruding body protrudes inwards in the radial direction relative to the radial position of the honeycomb body.

The invention relates to the field of propellers or rotors for airplanes, in particular to a bionic curved zigzag ducted rotor based on owl wings. A bionic curved zigzag ducted rotor wing based on an owl wing comprises a ducted body (1), a support (2) and a rotating shaft (3), the outer end of the support (2) is fixed on the inner side wall of the ducted body (1), the rotating shaft (3) is rotatably arranged at the center of the support (2), the bionic curved zigzag ducted rotor wing is characterized by further comprising at least two rotor wings (4), the rear ends of the rotor wings (4) are fixed on the rotating shaft (3), and the rotor wings (4) are evenly distributed around the rotating shaft (3). Namely, the connecting lines of the outer end points of all the rotor wings (4) form a line segment or a regular polygon with the rotating shaft (3) as the center, gaps are reserved between the front ends of the rotor wings (4) and the inner side wall of the duct body (1), and sawteeth (41) are arranged on the rear edges of the rotor wings (4). The pneumatic performance is excellent, and noise is reduced.

This invention provides an active flow control method and system based on intelligent algorithms. The method includes: determining the number of inlet parameter sets for a typical flight state point, constrained by simulation economy and sampling efficiency; performing numerical simulations according to the number of inlet parameter sets to obtain dataset 1, with inlet parameters as independent variables and flow field characteristics as dependent variables; obtaining dataset 2, with flight state as independent variables and flow field characteristics as dependent variables, through numerical simulation for a certain set of inlet parameters; constructing a proxy model of inlet flow field characteristics for a typical flight state point using deep learning based on dataset 1; constructing a proxy model of inlet flow field characteristics for a wide-speed-domain flight state based on the proxy model of inlet flow field characteristics for the flight state point, using a transfer learning algorithm and dataset 2; constructing an environment-agent interaction model based on a deep reinforcement learning algorithm, using the proxy model of inlet flow field characteristics for a wide-speed-domain flight state as the environment model for deep reinforcement learning; setting optimization termination conditions based on the environment-agent interaction model, and obtaining a control sequence with continuously optimal inlet performance under different flight states through deep reinforcement learning. This invention can stably adapt to flight scenarios with a wide speed range and a large airspace, and achieve real-time optimal control of the air intake flow field under a wide speed range, solving the problem of poor generalization ability of traditional methods under different operating conditions.

The application discloses a longitudinally foldable water-air dual-purpose propeller, and belongs to the technical field of cross-medium aircraft propulsion, comprising a new-configuration hub, a longitudinal folding mechanism, a limiting structure and a down-bending propeller blade with a preset down-bending angle; the configuration of the propeller enables the down-bending propeller blade to be completely unfolded to form a first working configuration through centrifugal force in air, and the down-bending propeller blade to be passively folded and limited to form a second working configuration through hydrodynamic lift in water; the longitudinally foldable water-air dual-purpose propeller can automatically complete mode switching according to the difference between working media without any active control mechanism, and can maintain high efficient propulsion performance in both media.

The invention belongs to the field of aviation, and discloses a rotor aerodynamic configuration of a light tilting rotorcraft. The light tilting rotorcraft rotor comprises the steps of overall parameter selection, airfoil profile selection, blade torsion angle distribution, blade chord length distribution, blade pneumatic analysis and the like. The designed light tilting rotorcraft rotor has high aerodynamic efficiency, can meet the aerodynamic requirements of different flight states, can meet the task requirements in the vertical take-off and landing stage, the hovering stage and the forward flight stage, meets the performance requirements of the light tilting rotorcraft, and has high practical value.

This invention discloses a plant protection drone for precision seeding, belonging to the field of agricultural drone technology. It includes a central body and four arc-shaped arms that can move relative to the central body. Each arm is equipped with a power unit and rotors. Driven by a deformation drive mechanism, the arms can switch between a cruising state (forming a circular shape) and an operational state (arching inward to form a three-dimensional structure). In the cruising state, the rotor planes are coplanar, resulting in high aerodynamic efficiency; in the operational state, the rotor planes are raised and moved away from the seeding device, effectively isolating the downwash airflow from interfering with the seeded material, significantly improving seeding accuracy and uniformity. This invention solves the technical problem of seeding drift caused by rotor wind fields in existing plant protection drones.

The utility model discloses an MIM (metal injection molding) turbocharging blade, which relates to the technical field of turbocharging blades and comprises a connecting seat, a group of blades are fixedly connected to the annular side surface of the connecting seat, two reinforcing ribs are fixedly connected between the group of blades, a group of grooves for turbulent flow are formed in the surface of each reinforcing rib, and a fixing rod is fixedly connected to the lower surface of the connecting seat. A connecting shaft is arranged on the lower surface of the fixing rod, the annular side face of the fixing rod is sleeved with a threaded ring in a threaded mode, the grooves in the surfaces of the blades can disturb airflow, the airflow forms a specific flow state on the surfaces of the blades, and the change of the flow state can increase the turbulence degree of the airflow and promote mixing of boundary layers. When the airflow flows through the blades, the airflow can flow in a mode of being attached to the surfaces of the blades, separation of the airflow on the surfaces of the blades and generation of vortexes are reduced, air resistance is reduced, the aerodynamic efficiency of the blades is improved, and then the turbocharging effect is enhanced.

This utility model discloses a blade, a propeller, and an aircraft, belonging to the field of aircraft technology. The blade includes a connected root and a shaft. The root has a root centerline, and the distance from the end of the blade furthest from the root to the root centerline is a first length. At the first position of the blade, the angle of attack is 18.38°±2.5°; at the second position, the angle of attack is 9.58°±2.5°; and at the third position, the angle of attack is 6.61°±2.5°. The distance from the first position of the blade to the root centerline is 20% to 25% of the first length; the distance from the second position of the blade to the root centerline is 50% to 58% of the first length; and the distance from the third position of the blade to the root centerline is 80% to 95% of the first length. The blade of this utility model, through the design of the angle of attack at multiple key positions of the main body of the propeller shaft, reduces air resistance and improves aerodynamic efficiency. The propeller and aircraft of this invention improve the aerodynamic efficiency of the propeller and the flight efficiency of the aircraft.

The utility model relates to the technical field of fan equipment, and provides a blade, a fan and an air conditioning system. The blade comprises a blade body, the front edge of the blade body forms a front edge curve, the front edge curve comprises a front convex section and a flat section, the front convex section is located on the side, close to the blade tip of the blade body, of the flat section, and the middle of the front convex section protrudes towards the front side of the blade body. The special structures of the front convex section and the flat section in the front edge curve have a good rectification effect on inlet turbulent flow groups, non-uniform flow is limited in a small forward swept area at the top of the blade, acting of the middle area of the blade is basically not affected, and a draught fan still has high aerodynamic efficiency under the condition that the inlet is shielded.

This invention proposes a symmetrically arranged cross-wing unmanned aerial vehicle (UAV) system, relating to the field of UAVs. It includes a fuselage structure, a power module, and a flight control module. The fuselage structure comprises a cylindrical fuselage and four wings symmetrically arranged in a cross pattern around the cylindrical surface of the fuselage; the four wings are arranged in an X-shape or a cross shape. The power module includes motors and propellers. The motors are located at the wingtips, with their output shafts aligned with the fuselage axis and facing the tail of the fuselage. The propellers are connected to the motor output shafts. The flight control module is located inside the fuselage and is used to control the output speed of the four motors. This system combines the advantages of a quadcopter FPV and a fixed-wing UAV, generating lift from the wings while also cruising and sprinting in fixed-wing form. Furthermore, by changing the motor speeds, it can control the pitch, yaw, and roll attitude of the UAV, eliminating the need for separate control surfaces, thus simplifying the structure and reducing costs.

The utility model belongs to the technical field of shape design and control of aircrafts, and relates to an electric tilt-rotor aircraft. Comprising a fuselage, two wings located on the two sides of the fuselage, an empennage, a plurality of supporting rods arranged below the wings and rotors arranged at the two ends of the supporting rods. The rotor wings comprise a plurality of tilting rotor wings and a plurality of fixed rotor wings; the number of the supporting rods is even, and the supporting rods are divided into two sets with the same number and are symmetrically arranged on the two sides of the machine body. A tilting rotor wing is arranged at the front end of each supporting rod; a fixed rotor wing is arranged at the rear end of each supporting rod; the tilting rotor wings are connected with the front ends of the supporting rods through tilting mechanisms, and the tilting mechanisms are used for adjusting the orientation of the tilting rotor wings. The electric tilting rotor aircraft provided by the utility model can realize the functions of vertical take-off and landing, tilting transition and cruise flight.

This utility model provides a sealing cylinder assembly and a blow molding equipment, relating to the field of blow molding equipment technology. The sealing cylinder assembly includes a sealing cylinder and a high-pressure valve group. The sealing cylinder includes a first end face and a receiving groove disposed on the first end face. The high-pressure valve group includes multiple valve cores and a valve cover structure. The valve cover structure includes at least one valve cover that is sealed to the sealing cylinder and covers the receiving groove. The valve cover can divide the receiving groove into at least one valve cavity, and each valve core is disposed in one valve cavity. This utility model can embed the valve cores of the high-pressure valve group into the valve cavities, making the shell of the sealing cylinder part of the shell of the high-pressure valve group, eliminating the need for an additional valve shell. Compared with the prior art, which manufactures and assembles the high-pressure valve group and the sealing cylinder separately, this reduces the number of parts and assembly complexity, lowers manufacturing and assembly costs, improves aesthetics, and helps to shorten the gas flow channel length and reduce gas loss.

The invention discloses a ducted hovercar and a working method thereof, and belongs to the technical field of hovercars. Four wheels of a hovercar body in the ducted hovercar are ducted wheels, and a ducted fan electric propulsion system is mounted in the ducted hovercar; a cockpit is arranged in the middle of the hovercar body, ducted fan electric propulsion systems are installed on the front portion and the rear portion of the cockpit respectively, and an openable and closable drag reduction protection mechanism is installed above the ducted fan electric propulsion systems. The ducted wheels are driven by a tilting control mechanism to move forwards and rotate outwards; the ducted fan electric propulsion system in the middle provides main power in the take-off preparation stage and the descending hovering stage, and the ducted fan electric propulsion systems in the four ducted wheels provide main power in the stable flight stage. The power of the aircraft and automobile wheels are effectively combined, stable conversion between a flying mode and a land mode can be achieved, and the aircraft is more like a flying automobile instead of a vertical take-off and landing aircraft.

The utility model discloses a multifunctional screw conveying device capable of conveying gas in two directions, which comprises a cylinder body, a first main shaft and a second main shaft are arranged in the cylinder body side by side, a symmetrical molded line male screw is mounted on the first main shaft, a symmetrical molded line female screw is mounted on the second main shaft, and the first main shaft and the second main shaft are arranged in parallel. The symmetrical molded line male screw and the symmetrical molded line female screw are meshed with each other in a sealed mode, a first gas transmission port and a second gas transmission port which can be commonly used with each other are formed in the two ends of the cylinder body respectively, any one of the first gas transmission port and the second gas transmission port serves as a gas suction port, and the other one serves as a gas exhaust port. A synchronous linkage structure is arranged between the first main shaft and the second main shaft, one end of one of the first main shaft and the second main shaft is connected with a main shaft of a motor, and the motor is provided with a matched frequency converter. The one-way gas conveying device can solve various problems caused by the fact that an existing one-way gas conveying device needs to achieve two-way gas conveying.

The application provides a three-dimensional flow impeller blade profile for a high-speed turbine vacuum pump and a design method thereof. f ( m ) is determined by a loading law function, f ( m ) is a segmented function composed of a front loading segment, a main loading segment and a rear loading segment, and the function value and the first derivative are continuous at each segmented point. The application finely controls the work distribution in the impeller flow passage through the loading law function, and suppresses the angle area separation and secondary flow loss under high speed. The front loading segment design adopted by the application improves the low attack angle adaptability of the blade leading edge, the slow change design of the rear loading segment reduces the outlet distortion, and the surge margin and blockage margin of the impeller are both expanded. The application is specially adapted to the loading law of the rarefied gas flow with the inlet pressure of the centrifugal vacuum pump being as low as 20 kPa, and avoids the laminar separation problem easily occurring under low Reynolds number in the conventional design. In addition, the application also has the advantages of strong universality and the like.

The invention relates to an outlet guide vane, a power propulsion system and a noise reduction method of the power propulsion system. The outlet guide vane comprises a vane body, and the vane body comprises an acoustic lining part; the acoustic liner part is at least provided with a plurality of acoustic liner areas in the direction from the front edge to the tail edge of the outlet guide vane, and the acoustic liner areas at least comprise the first acoustic liner area and the second acoustic liner area located on the upstream of the first acoustic liner area. Wherein the first acoustic liner region comprises a plurality of first resonant cavities, the second acoustic liner region comprises a plurality of second resonant cavities, and the area of a single first resonant cavity is larger than that of a single second resonant cavity.

The invention discloses a bionic shark fin type tongue opening noise reduction centrifugal fan, and belongs to the technical field of centrifugal fan structure improvement, the bionic shark fin type tongue opening noise reduction centrifugal fan comprises a fan body, a flow guide plate is installed at the air outlet position of an inner tongue opening of the fan body, the flow guide plate is of a shark fin structure, the flow guide plate comprises a main plate, and the main plate is provided with a front edge side, a tail end side and a bottom end side; the transverse projection of the front edge point on the front edge side is arc-shaped; on the cross section of the main plate, the shape of the pipeline close to the air outlet low-speed side is shrunk from the front edge side to the tail end side, and the shape of the pipeline close to the air outlet high-speed side is shrunk and then expanded from the front edge side to the tail end side; the tail end side is sequentially provided with an arc section, a nearly linear section and an S-shaped bent section from top to bottom, and the bottom end side is of a plane structure and is parallel to the air outlet of the fan body in the horizontal direction. The power utilization of the centrifugal fan can be improved, and the noise of the centrifugal fan can be reduced.

The application discloses a kind of wing-body fusion layout unmanned aerial vehicle's aerodynamic shape, it is related to low-altitude economic unmanned aerial vehicle high lift-drag ratio flight technical field, including wing-body part, the rear end of the upper surface of wing-body part is equipped with V-tail, engine is installed between the opposite surface of V-tail, the wing-body part with the V-tail is equipped with control surface part on;The lower surface of wing-body part is equipped with landing gear;The wing-body part includes inner wing and outer wing, the inner wing with the outer wing is symmetrically arranged, the edge of outer wing is equipped with wing tip;The leading edge sweep angle of wing-body part is 20 °, the trailing edge sweep angle of wing-body part is 17 °.The application discloses a kind of wing-body fusion layout unmanned aerial vehicle's aerodynamic shape, has better aerodynamic performance, stronger carrying capacity and lower noise;Appearance is simple, and cruise efficiency is high, suitable for engineering practical application.

The utility model provides a foldable trailing edge flying wing unmanned aerial vehicle, and relates to the technical field of unmanned aerial vehicles, the foldable trailing edge flying wing unmanned aerial vehicle comprises a main wing, the main wing comprises a main wing inner section and a main wing outer section, the wingtip of the main wing outer section is connected with a small wing, and the trailing edge of the main wing outer section is connected with a connecting wing and an empennage; the winglet is connected with the connecting wing through a driving rotating shaft, the connecting wing is connected with the empennage through a driven hinge, and the empennage is connected with the main wing inner section through a driven hinge; and the front parts of the connecting wing and the empennage are connected with the main wing outer section through a locking structure. When the multi-wing unmanned aerial vehicle is used for executing complex maneuvering actions such as emergency avoidance, large-attack-angle climbing and small-radius turning, the winglet, the connecting wing and the empennage are folded under the driving of the wingtip driving rotating shaft, so that a connecting wing layout is formed. The wing surfaces are converted into a three-dimensional structure from the same plane, so that an additional stabilizing plane is added for the flying wing unmanned aerial vehicle, and meanwhile, additional torque is provided for the unmanned aerial vehicle to execute complex maneuvering actions.

The invention discloses an efficient complex curved surface volute design method. The method comprises the steps that a centrifugal impeller, a vaneless diffuser and a volute are cooperatively designed; the method comprises the following steps: selecting initial design parameters of a volute, selecting circular section design of the volute according to a momentum moment conservation principle, performing initial design of the volute according to gas conditions at an outlet of the vaneless diffuser, establishing a flow channel fluid model of the volute according to a three-dimensional model of the volute, and calculating a flow field of the flow channel fluid model. A fluid model of a volute flow channel is established through the three-dimensional model of the volute, the fluid model and the fluid model of the centrifugal impeller are subjected to coupling calculation, and the comprehensive aerodynamic efficiency eta of the centrifugal impeller and the volute is obtained; and judging that the comprehensive aerodynamic efficiency eta meets the design requirement until the design requirement is met. According to the design method, the aerodynamic efficiency between the volute and the centrifugal impeller can reach the optimal matching state, the energy conversion efficiency of a pneumatic system is improved, and energy loss caused by the volute is reduced.

The utility model discloses a distributed power short-distance take-off and landing aircraft which comprises an aircraft body, a left wing, a right wing and an empennage assembly, a plurality of power cabins are arranged on the left wing and the right wing at intervals, the power cabins are arranged below the left wing and the right wing respectively, and propellers are connected with the power cabins and provide power for flying; the size and spacing of the propellers and the included angle between the axis of the propellers and the chord line of the wings are defined according to pneumatic requirements, so that the power lift augmentation efficiency is higher; flaps with large elongation and large chord length are arranged on the rear sides of the wings and can deflect at a large angle, so that the voyage and the loading efficiency of the aircraft are improved while larger lift force is provided for the aircraft and the take-off and landing distance is shortened.

This invention discloses an engine intake mechanism, an engine system, and a vehicle, belonging to the field of engine technology. The engine intake mechanism of this invention makes the inner wall of the airflow guide passage smoother; in other words, there are no geometric abrupt changes in the inner wall of the airflow guide passage. This reduces flow losses in the airflow guide passage, resulting in smaller variations in airflow velocity. Consequently, the airflow pressure and velocity at the turbocharger inlet are more uniform, improving aerodynamic efficiency and thus increasing boost efficiency. The engine system and vehicle of this invention, by applying the aforementioned engine intake mechanism, can improve the engine system's power performance and fuel economy, and enhance the driving experience.

This invention provides a centrifugal compressor and its impeller, wherein the impeller includes a plurality of blades arranged circumferentially, with a flow channel formed between each pair of adjacent blades; each blade is backward-curved, gradually bending away from the impeller's rotation direction from its inlet end to its outlet end; and in the direction from the inlet end to the outlet end, the thickness of each blade first gradually increases and then gradually decreases. The impeller of this invention has higher aerodynamic efficiency, which is beneficial for miniaturizing the centrifugal compressor.

The invention relates to the technical field of electrical products, and discloses a centrifugal wind wheel, a centrifugal fan and a device with the centrifugal fan, the centrifugal wind wheel comprises a plurality of fan blades arranged in the circumferential direction, and the thicknesses of the fan blades are gradually increased and then gradually reduced in the direction away from the center of the centrifugal wind wheel. And an overflowing gap between every two adjacent fan blades is gradually increased and then gradually reduced. The direction far away from the center of the centrifugal wind wheel is actually the wind outlet direction, the overflowing gaps between every two adjacent fan blades are gradually increased and then gradually decreased in the wind outlet direction, the overflowing gaps are increased so that wind can smoothly enter the overflowing gaps, the overflowing gaps are decreased so that the airflow speed can be increased, and therefore airflow can be accelerated when flowing through the overflowing gaps; vortex at the inlet of the fan blade can be eliminated, efficiency can be improved, and noise can be reduced.