A high-efficiency lift-augmenting flow control device suitable for large thickness airfoils

Abstract

The application discloses a high-efficiency lift-increasing flow control device suitable for a large-thickness airfoil, wherein a gas flow injection member is arranged on a pressure surface and located upstream of a free flow stagnation point, and adopts an inwardly inclined discharge angle of 0-5 degrees; a gas flow recovery member is arranged at the rear of a suction surface. A circulating driving member sucks low-momentum boundary layer fluid at a trailing edge, discharges the pressurized fluid from the injection member, and forms a zero-mass closed loop. In a positive angle of attack working condition, the injected gas exchanges momentum with the flow upstream of the stagnation point, further pushes the stagnation point position to the pressure surface, and expands the range of the negative pressure area at the front edge of the suction surface; meanwhile, the inwardly inclined discharge angle utilizes the wall adhesion effect of the large-curvature front edge to make the injected gas stably flow along the front edge, and forms a concentrated and strong negative pressure concentration area. The device can greatly increase the maximum lift coefficient, delay the stall angle of attack, and has a simple structure and no exposed moving parts, thereby providing a high-efficiency lift-increasing solution for a short-takeoff-and-landing aircraft.

Description

Technical Field

[0001] This application relates to the field of aircraft aerodynamic performance enhancement technology, and more specifically, to a high-efficiency lift enhancement device and its control method that optimizes parameters for the aerodynamic characteristics of thick airfoils and utilizes the wall adhesion effect to achieve flow control in the leading edge region. Background Technology

[0002] In general aviation, short-haul regional transportation, agricultural operations, and high-altitude long-endurance unmanned aerial vehicles (UAVs), aircraft widely adopt thick airfoils with a maximum relative thickness between 12% and 30%. These airfoils offer two significant advantages: first, the thicker airfoil profile provides ample internal structural space, facilitating the placement of fuel, landing gear, and various onboard systems; second, the thick airfoil exhibits smoother stall characteristics and better lift retention at low speeds, making it suitable for the aerodynamic requirements of takeoff and landing.

[0003] However, under high angle-of-attack conditions during takeoff and landing, the suction surface (upper surface) of a thick airfoil is highly susceptible to large-scale flow separation. This is because the surface curvature of a thick airfoil varies significantly. As the angle of attack increases, the adverse pressure gradient behind the suction surface intensifies sharply. Low-energy fluids within the boundary layer cannot overcome this gradient and detach from the airfoil, forming a large-area separation zone. Once flow separation occurs, the airfoil's lift coefficient drops sharply, while its drag coefficient increases dramatically, severely restricting the aircraft's takeoff and landing performance and high angle-of-attack maneuverability.

[0004] To address these issues, conventional methods include installing mechanical lift-enhancing devices such as leading-edge slats and trailing-edge flaps on the wings. However, these mechanical devices are complex in structure, have considerable weight, and require sophisticated drive and transmission mechanisms, significantly increasing manufacturing and maintenance costs, while also generating additional aerodynamic noise.

[0005] In the field of active flow control, various techniques exist for improving airfoil aerodynamic performance using fluid injection or suction. Among these, leading-edge rotating cylinder control is an effective method that has been experimentally verified. Experimental studies conducted by Saad Ahmed et al. on the NACA0024 airfoil using leading-edge rotating cylinder control showed that, with a cylindrical surface velocity ratio Uc / U = 4, the airfoil's maximum lift coefficient could be increased from 0.85 to 1.63, and the stall angle of attack could be delayed by approximately 160%. This experimental result demonstrates that applying active flow control to the leading-edge region of thick airfoils has significant lift-enhancing potential. However, the leading-edge rotating cylinder scheme requires the installation of a rotatable cylinder and its drive mechanism at the leading edge, resulting in a complex structure. Furthermore, rotating the cylinder during cruise increases additional drag, which is detrimental to the aircraft's cruise efficiency.

[0006] Another known flow control scheme involves creating airflow inlets and suction outlets on the airfoil surface to form a closed-loop flow control system. However, existing schemes typically place the airflow inlet at the front of the suction face, where the free flow stagnation point is located on the pressure face under positive angle-of-attack conditions. In this configuration, the injected airflow flows directly backward along the suction face, undergoing strong shear mixing with the mainstream over a long chordal distance, resulting in significant energy dissipation. Simultaneously, the injected airflow cannot alter the location of the free flow stagnation point, limiting its ability to regulate the leading-edge pressure distribution and making it difficult to fully utilize the enhanced wall adhesion effect of the large curvature radius at the leading edge of a thick airfoil. Furthermore, existing schemes lack specific optimization for the injection angle of thick airfoils. When the injected airflow flows around the large curvature leading edge, an inappropriate injection angle can easily lead to premature separation or unstable wall adhesion.

[0007] Therefore, there is an urgent need for a flow control scheme specifically optimized for the aerodynamic characteristics of thick airfoils. In particular, by changing the relative positional relationship between the injection component and the stagnation point on the leading edge of the airfoil, and optimizing the discharge angle of the injected airflow, the leading edge pressure distribution can be regulated by utilizing the pre-interaction between the injected airflow and the free flow upstream of the stagnation point under positive angle of attack conditions. This would fully leverage the amplifying effect of the large curvature leading edge on the wall adhesion effect, and achieve excellent low-speed high-lift performance while maintaining structural simplicity. Summary of the Invention

[0008] (a) Purpose of the invention

[0009] This application aims to provide a flow control device specifically designed for optimizing the aerodynamic characteristics of thick airfoils. By placing the airflow injection component on the pressure surface and upstream of the free flow stagnation point, and precisely configuring its chordal position and discharge angle, the device utilizes the momentum exchange between the injected gas and the high-energy incoming flow to shift the stagnation point position under positive angle-of-attack conditions. Combined with the enhanced wall adhesion effect of the large curvature leading edge, it achieves significant lift enhancement and stall delay effects over a wide range of large angles of attack. Furthermore, the device has a simple structure and is easy to implement in engineering.

[0010] (II) Technical Solution

[0011] To achieve the above objectives, this application provides the following technical solution:

[0012] A high-efficiency lift-enhancing flow control device suitable for thick airfoils, wherein the maximum relative thickness of the airfoil is in the range of 12% to 30%, comprising:

[0013] The airfoil body has a leading edge endpoint, a trailing edge endpoint, a suction surface, and a pressure surface. Under positive angle of attack conditions, the leading edge region of the airfoil body has a free flow stagnation point, which is located on the pressure surface.

[0014] The airflow injection component is located on the pressure surface of the airfoil body, and under positive angle of attack conditions, it is located upstream of the free flow stagnation point, that is, on the pressure surface arc segment between the leading edge endpoint and the stagnation point;

[0015] An airflow recovery component is provided in the trailing edge region of the suction surface of the airfoil body;

[0016] A circulating drive component is built into the airfoil body. Its air intake port is connected to the airflow recovery component, and its exhaust port is connected to the airflow injection component. When the circulating drive component is running, it extracts the low momentum boundary layer fluid from the rear section of the suction surface from the airflow recovery component, pressurizes it, and discharges it from the airflow injection component. The mass flow rate of the discharged gas is equal to the mass flow rate of the extracted gas.

[0017] Under positive angle of attack conditions, the pressurized gas discharged from the airflow injection component adheres to the leading edge surface of the airfoil body based on the wall adhesion effect and flows around to the suction surface, forming a negative pressure concentration area in the leading edge region, thereby delaying the airfoil's stall critical angle of attack by at least 100° and significantly increasing the maximum lift coefficient.

[0018] "Flow adhering to the airfoil tip" is key to the Coanda effect. For the jet to stably flow along the leading edge and adhere to the suction surface, the initial direction of the jet must be conducive to enhancing the adhesion effect. For thick airfoils, the leading edge region has a large radius of curvature and a gentle curvature change, making it easier to maintain the wall adhesion effect. The discharge angle of the injected gas directly affects the stability of its flow along the leading edge and adhering to the wall. If the angle between the discharge direction and the local tangent direction is positive (outward deviation from the airfoil), the injected gas will directly detach from the pressure surface, failing to achieve wall adhesion flow around the leading edge, the negative pressure concentration zone cannot be formed, and the control effect is completely lost. If the discharge direction is almost completely tangential (0°), due to the gentle curvature of the leading edge of the thick airfoil, the injected gas has a sufficient pressure gradient towards the wall during the flow, and can still maintain stable adhesion. Therefore, thick airfoils have a lower limit requirement for the injection angle; 0° is sufficient to meet the adhesion requirements. If the inward inclination angle of the discharge direction is too large (greater than 5°), the injected gas points inward at a large angle, which, while enhancing the pressure gradient towards the wall, may cause the injected gas to directly impact the pressure surface wall after ejection, resulting in momentum loss and local flow turbulence. Simultaneously, an excessively large inclination angle causes the injected gas to undergo a more abrupt directional change when turning around the leading edge, increasing energy dissipation and reducing both the velocity and the intensity of the negative pressure zone upon reaching the suction surface. Through fluid dynamics analysis and numerical simulation optimization for thick airfoils such as NACA0025, an inclination angle range of 0° to 5° achieves the optimal balance between the pressure gradient towards the wall and momentum maintenance. Preferably, for the NACA0025 airfoil, an inclination angle of 2° to 4° yields the best wall adhesion stability and the intensity of the leading-edge negative pressure concentration zone.

[0019] Within this angular range, the injected gas acquires a moderate normal velocity component pointing towards the wall (or remains tangential) when leaving the injection port, utilizing the geometric advantages of the large curvature leading edge to achieve stable adhesion flow around the gas, forming a concentrated and intense negative pressure zone.

[0020] In a further preferred embodiment, the circulating drive component includes at least one of a miniature compressor, an electric booster rotor, or a positive displacement air pump, the rated output capacity of which meets the requirements for providing the required gas circulation mass flow rate during takeoff and landing.

[0021] A further preferred embodiment also includes a control unit, which can adjust the operating power of the cyclic drive component according to the current airfoil angle of attack and flight phase commands, so as to minimize the total energy consumption of the system while keeping the drag coefficient non-positive.

[0022] This application also provides a lift enhancement system for a short takeoff and landing aircraft, comprising the high-efficiency lift enhancement flow control device described in any of the above claims.

[0023] This application also provides a low-speed aircraft that includes the aforementioned short takeoff and landing aircraft lift enhancement system.

[0024] This application also provides a flow control method for airfoils with large thickness, applicable to airfoils with a maximum relative thickness in the range of 12% to 30%, comprising:

[0025] On the pressure surface of the airfoil, and at a position upstream of the free flow stagnation point under positive angle of attack conditions, pressurized gas is discharged in a direction with an inward inclination angle of 0° to 5° with the local tangent direction of the pressure surface;

[0026] By utilizing the wall adhesion effect in the leading edge region of the airfoil, the pressurized gas flows stably around the leading edge to the suction surface, and a concentrated negative pressure zone is generated in the leading edge region.

[0027] Meanwhile, at the trailing edge of the airfoil suction surface, low momentum boundary layer fluid near the wall is extracted, and the mass flow rate of the discharged gas is kept equal to the mass flow rate of the extracted gas.

[0028] During takeoff and landing, the intensity of the negative pressure zone is controlled by controlling the mass flow rate of the gas circulation, thereby achieving increased lift, reduced drag, or thrust generation.

[0029] (III) Beneficial Effects

[0030] Compared with existing technologies, this application has the following significant advantages under positive angle of attack conditions:

[0031] (1) Parameter optimization for thick airfoils achieves a breakthrough in lift performance: By arranging the airflow injection component on the pressure surface and upstream of the stagnation point (between the leading edge endpoint and the stagnation point), and using an inward discharge angle of 0° to 5°, this application fully releases the potential for enhancing the wall adhesion effect of the large curvature leading edge. The appropriate inward angle provides the necessary wall pressure gradient for the injected gas, ensuring its stable adhesion on the large curvature leading edge. Numerical simulation data show that for the NACA0025 airfoil, when the gas circulation mass flow rate is 0.1385 kg / s, the maximum lift coefficient jumps from 0.979 in the uncontrolled state to 4.209, an increase of 330%; when the mass flow rate is 0.2 kg / s, the maximum lift coefficient further increases to 6.453, an increase of up to 559%.

[0032] (2) Significantly delays the stall critical angle of attack and greatly expands the usable flight boundary: This application utilizes the momentum exchange between the injected gas and the incoming flow upstream of the stagnation point to push the location of the incoming flow stagnation point towards the pressure surface, thereby expanding the negative pressure zone at the leading edge of the suction airfoil; at the same time, the optimized inward discharge angle ensures the stability of the injected gas flow around the leading edge and adheres to the wall, forming a concentrated negative pressure zone, which effectively suppresses the flow separation phenomenon that is very easy to occur on the suction surface of a thick airfoil at high angles of attack. For the NACA0025 airfoil, the stall critical angle of attack is delayed from 15° in the uncontrolled state to 38° (mass flow rate 0.1385 kg / s) and even 56° (mass flow rate 0.2 kg / s), a delay of 23° to 41°.

[0033] (3) Significantly improved energy utilization efficiency based on wall adhesion effect: This application utilizes the geometric characteristics of the large curvature radius of the leading edge of the thick airfoil and precisely controls the discharge angle of the injected gas (3° to 8° inward inclination) to enable the injected gas to flow stably around the leading edge to the suction surface based on the wall adhesion effect. The appropriate inward inclination angle enhances the pressure gradient driving effect between the injected gas and the leading edge surface, allowing it to maintain high kinetic energy during the flow. In this process, the kinetic energy of the injected gas is efficiently converted into high flow velocity and low static pressure in the leading edge region, forming a concentrated negative pressure zone. This negative pressure zone acts on the entire airfoil suction surface in the form of a pressure gradient, and the energy utilization efficiency is much higher than that of the traditional method of directly injecting airflow into the suction surface.

[0034] (4) Simple structure and strong engineering feasibility: This application integrates the cyclic drive component entirely within the airfoil body, eliminating the need for an external air source and maintaining the aerodynamic complexity of the aircraft. Compared to solutions requiring movable parts (such as rotating cylinders, movable flaps, etc.) to be installed on the airfoil surface, the device in this application has no exposed moving parts, resulting in higher reliability and lower maintenance requirements. The optimized small-sized opening and specific injection angle have limited impact on the structural strength and internal space layout of the airfoil body, demonstrating good engineering adaptability and modification feasibility.

[0035] (5) Excellent drag control potential: While generating a significant increase in lift, the projection component of the negative pressure concentration area at the leading edge in the direction of the incoming flow can generate considerable leading edge suction, effectively offsetting the pressure drag at the rear of the airfoil. With appropriate adjustment of the gas circulation mass flow rate, the drag coefficient of the airfoil can be reduced over a wide angle of attack range, further improving the aerodynamic efficiency of the aircraft.

[0036] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0037] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0038] Figure 1 This is a schematic diagram of the structural arrangement of the device in this application on a thick airfoil (NACA0025).

[0039] Figure 2 This is a schematic diagram of the working principle of the device in this application, showing the momentum exchange between the injected gas and the free flow upstream of the stagnation point, the flow trajectory around the leading edge and the negative pressure concentration area at the leading edge under positive angle of attack conditions.

[0040] Figure 3 The lift coefficients of the device in this application, the comparative configuration (the configuration where the airflow inlet is located on the suction surface), and the uncontrolled airfoil are shown as curves of change with angle of attack under different gas circulation mass flow rates.

[0041] Figure 4 The drag coefficients of the device in this application, the comparative configuration, and the uncontrolled airfoil vary with angle of attack under different gas circulation mass flow rates.

[0042] Figure 5 The jet flow characteristics at the injection component are compared between the device of this application and the comparative configuration under different gas circulation mass flow rates.

[0043] Figure 6 The suction momentum characteristic values ​​at the recovery component are compared between the device of this application and the comparative configuration under different gas circulation mass flow rates.

[0044] Figure 7 The Mach number distribution and surface streamlines of the device in this application are compared with those of the comparative configuration under the condition of a mass flow rate of 0.1385 kg / s and an angle of attack of 36°. (a) is the comparative configuration (conventional CFJ airfoil), and (b) is the airfoil of this invention.

[0045] Figure 8The Mach number distribution and surface streamlines of the device of this application are compared with those of the comparative configuration under the condition of mass flow rate of 0.2 kg / s and angle of attack of 38°. (a) is the comparative configuration (conventional CFJ airfoil), and (b) is the airfoil of this invention.

[0046] Figure 9 The pressure coefficient distribution cloud diagrams of the device of this application and the comparative configuration are compared at a mass flow rate of 0.099 kg / s and an angle of attack of 22°. (a) is the comparative configuration (conventional CFJ airfoil), and (b) is the airfoil of this invention. Detailed Implementation

[0047] This application addresses the technical problem of suction surface flow separation and limited lift coefficient in thick airfoils under high angle-of-attack conditions during takeoff and landing. Existing solutions, such as leading-edge rotating cylinder control technology, can achieve certain results, but they require the installation of a rotating cylinder and its drive mechanism on the airfoil's leading edge, resulting in complex structure, increased weight, and additional drag introduced during cruise. Furthermore, traditional airflow injection schemes place the injection port in front of the suction face, causing the injected airflow to flow directly backward along the suction face, resulting in long-distance strong shear mixing with the mainstream and significant energy dissipation. Under positive angle-of-attack conditions, they cannot change the location of the incoming flow stagnation point, limiting their ability to control the leading-edge pressure distribution. Simultaneously, existing solutions lack specific optimization for the injection angle of thick airfoils, failing to fully utilize the enhanced wall adhesion effect of the large radius of curvature at the leading edge of thick airfoils.

[0048] The innovative mechanism of this application lies in the following: Under positive angle-of-attack conditions, the airflow injection component is moved from the traditional suction surface to the pressure surface and located upstream of the free flow stagnation point (i.e., between the leading edge endpoint and the stagnation point), with an inward discharge angle of 3° to 8°. In the flow around the airfoil at a positive angle of attack, the stagnation point is the position where the free flow first contacts the airfoil surface and its velocity drops to zero, located on the pressure surface; the region upstream of the stagnation point is the area where the incoming flow has not yet been impeded by the airfoil and still maintains high kinetic energy. When the pressurized gas is discharged from this region at a moderate inward angle, it first encounters the high-kinetic-energy free flow and undergoes momentum exchange, further pushing the actual stagnation point of the incoming flow towards the pressure surface, thereby expanding the negative pressure zone at the leading edge of the suction surface. At the same time, the inward discharge angle provides the necessary wall pressure gradient for the injected gas, allowing it to adhere tightly to the leading edge surface and flow stably under the wall adhesion effect. Its kinetic energy is converted into high velocity and low static pressure of the leading edge flow, forming a concentrated and strong negative pressure zone in the leading edge region of the airfoil. This negative pressure zone acts directly on the entire suction surface through a pressure gradient, resulting in a much stronger entrainment and acceleration effect on the mainstream compared to traditional methods. Furthermore, the airflow recovery component located at the rear of the suction surface continuously removes low-momentum boundary layer fluid near the wall, reducing the boundary layer thickness and further suppressing flow separation.

[0049] This application ultimately achieves significant lift coefficient enhancement, substantial delay of stall critical angle of attack, and effective reduction of drag coefficient with a simple structural configuration under positive angle of attack conditions, providing a lift enhancement solution for short takeoff and landing aircraft that combines high efficiency and high reliability.

[0050] The technical solution of this application will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only for explaining this application and do not constitute a limitation on the scope of protection of this application. This application is mainly designed to meet the lift enhancement requirements of aircraft at positive angles of attack (e.g., takeoff, climb, and landing phases).

[0051] This embodiment uses the NACA0025 airfoil as the application example. This airfoil has a maximum relative thickness of 25% and a large radius of curvature in the leading edge region, making it a typical representative of thick, low-speed airfoils. The airfoil chord length c = 1.125m. The free-flow Mach number Ma = 0.1, the flight altitude is 10km, corresponding to a static pressure of 26499.9Pa and a static temperature of 223.252K.

[0052] like Figure 1 As shown, the device of this application includes a NACA0025 airfoil body, on which an airflow injection component located on the pressure surface and an airflow recovery component located behind the suction surface are provided. Under positive angle of attack conditions, the free flow stagnation point is located on the pressure surface, and the airflow injection component is located upstream of the stagnation point, that is, on the pressure surface arc segment between the leading edge endpoint and the stagnation point.

[0053] In this embodiment, the distance between the center of the opening of the airflow injection component and the stagnation point of the free flow is 2% of the chord length. In the flow around the positive angle of attack of the airfoil, the free flow, upon approaching the airfoil, first drops to zero velocity at the stagnation point located on the pressure surface and bifurcates into upper and lower flows. The region upstream of the stagnation point is where the incoming flow is not yet impeded by the airfoil, and the incoming flow still maintains high kinetic energy. By placing the injection component here, the exhaust gas, after being ejected, first encounters the high-kinetic-energy free flow and undergoes momentum exchange. The high momentum of the injected gas can further push the actual stagnation point position of the incoming flow towards the pressure surface. The downward shift of the stagnation point position brings two direct effects: first, the streamline curvature of the leading edge of the suction front increases, the airflow acceleration effect is enhanced, and the negative pressure zone expands; second, the flow path of the injected gas around the leading edge obtains more sufficient space for the development of the wall adhesion effect, and the wall adhesion stability is enhanced.

[0054] If the injection component is too close to the stagnation point, the injected gas will quickly encounter a low-speed, high-pressure zone near the stagnation point after ejection, resulting in insufficient momentum exchange and limited ability to move the stagnation point. If the injection component is too far from the stagnation point, it means that the injection component is extremely close to the leading edge endpoint, and the arc length of the injected gas reaching the leading edge after ejection is too short, failing to obtain sufficient development distance to form a stable wall-attached flow, making separation prone to occur at the abrupt change in curvature at the leading edge. In this embodiment, a position of 2% chord length is selected, which ensures both sufficient momentum exchange distance to effectively move the stagnation point and stability of the flow development around the stagnation point.

[0055] The inward angle between the discharge direction of the airflow injection component and the local tangent direction of the pressure surface is 3°. This angle is preferably in the range of 0° to 5°, and more preferably 2° to 4°.

[0056] For thick airfoils, the leading edge region has a large radius of curvature and a gentle curvature change, making it easier to maintain wall adhesion. If the exhaust angle is positive, the injected gas will detach from the airfoil and fail. If the exhaust angle is nearly tangential (0°), the large curvature leading edge can still provide sufficient pressure gradient towards the wall to maintain adhesion. If the exhaust angle is too inward (greater than 5°), the injected gas may directly impact the wall, causing momentum loss. In this embodiment, an inward angle of approximately 3° is selected, achieving an optimal balance between the pressure gradient towards the wall and momentum maintenance. The injected gas acquires a moderate normal velocity component pointing towards the wall when leaving the injection port, utilizing the geometric advantages of the large curvature leading edge to achieve stable adhesion flow around the airfoil, forming a concentrated and strong negative pressure zone.

[0057] The normal opening height of the airflow injection component is set to 0.00256c. A smaller relative opening height helps increase the exhaust velocity of the injected gas, thereby enhancing the peak intensity of the leading-edge negative pressure concentration zone while reducing the impact on the airfoil's main structure. The opening center of the airflow recovery component is located on the suction surface at a chordal distance of approximately 0.773c from the leading-edge endpoint. This location corresponds to the high-incidence area of ​​flow separation behind the suction surface at high angles of attack in thick airfoils. Its normal opening height is set to 0.01022c, approximately four times the opening height of the injection component, to accommodate the characteristics of low-momentum boundary layer fluid velocity and high volumetric flow rate.

[0058] The circulating drive component, in this embodiment, employs a miniature compression mechanism built into the airfoil body. It is connected to the outlet of the airflow recovery component and the inlet of the airflow injection component via internal airflow pipes. This component draws in low-momentum gas from the boundary layer from the recovery component, pressurizes it, and discharges it from the injection component, maintaining the discharge mass flow rate equal to the suction mass flow rate, forming a zero-mass-flow closed-loop flow. This closed-loop design allows the device to operate continuously with only internal power input, eliminating the need for an external gas source.

[0059] like Figure 2As shown, under positive angle-of-attack conditions, the pressurized gas discharged from the airflow injection component at an inclination angle of approximately 3° exchanges momentum with the free flow upstream of the stagnation point, further pushing the actual stagnation point of the incoming flow towards the pressure surface. Subsequently, the injected gas, based on the wall adhesion effect, flows stably around the airfoil's leading edge surface to the suction surface, forming a concentrated and intense negative pressure concentration zone in the leading edge region. This negative pressure concentration zone significantly increases the overall circulation of the airfoil, thereby generating a huge increase in lift. Simultaneously, the airflow recovery component continuously removes the near-wall low-momentum boundary layer fluid behind the suction surface, further suppressing flow separation.

[0060] The numerical simulation employed a CFD method to solve the Reynolds-averaged Navier-Stokes equations, with the k-ω SST model selected as the turbulence model. Comparative simulations were conducted on the uncontrolled NACA0025 airfoil, a comparative configuration (a conventional CFJ configuration with the airflow inlet located on the suction surface), and the airfoil of the device described in this application, under three operating conditions: gas circulation mass flow rates of 0.099 kg / s, 0.1385 kg / s, and 0.2 kg / s.

[0061] Lift characteristics analysis: such as Figure 3 As shown, under three mass flow rates, the maximum lift coefficient and stall critical angle of attack of the device in this application are significantly improved and far superior to the comparative configuration.

[0062] At a mass flow rate of 0.099 kg / s, the maximum lift coefficient of the device in this application is increased from 0.979 in the uncontrolled state to 2.866 (an increase of 193%), and the stall critical angle of attack is delayed from 15° to 27° (a delay of 12°).

[0063] At a mass flow rate of 0.1385 kg / s, the maximum lift coefficient of the device in this application is increased from 0.979 to 4.209 (an increase of 330%), and the stall critical angle of attack is delayed from 15° to 38° (a delay of 23°). In contrast, the maximum lift coefficient of the comparative configuration is only increased to 3.760, and the stall critical angle of attack is delayed to 36°. The maximum lift coefficient of the device in this application is 0.449 higher than that of the comparative configuration.

[0064] At a mass flow rate of 0.2 kg / s, the maximum lift coefficient of the device in this application is increased from 0.979 to 6.453 (an increase of 559%), and the stall critical angle of attack is delayed from 15° to 56° (a delay of 41°).

[0065] The above calculation data fully demonstrates that by setting the airflow injection component upstream of the stagnation point and adopting an optimized inward discharge angle, this application effectively shifts the stagnation point position under positive angle of attack conditions, ensuring stable adhesion of the injected gas and achieving a maximum lift coefficient several times that of an uncontrolled airfoil.

[0066] Resistance characteristic analysis: such as Figure 4As shown, the device of this application can significantly reduce the drag coefficient under all test conditions, and even generate negative drag (net thrust) over a wide angle of attack range. With the increase of gas circulation mass flow rate, the absolute value and effective range of the negative drag further expand. This effect stems from the leading-edge suction generated by the projected component of the negative pressure concentration area in the incoming flow direction, effectively counteracting the pressure drag at the rear of the airfoil.

[0067] Comparison of momentum eigenvalues: such as Figure 5 and Figure 6 As shown, under the same gas circulation mass flow rate conditions, the jet momentum coefficient at the injection component and the suction momentum coefficient at the recovery component of the device in this application are both lower than those of the comparative configuration. This means that the device in this application achieves better lift and drag reduction benefits with less jet momentum input, fully demonstrating the significant superiority of this application in terms of energy utilization efficiency. The principle is that this application utilizes upstream injection at the stagnation point, an optimized inward discharge angle, and the wall adhesion effect to transform the energy transfer path from "direct turbulent mixing" to "momentum exchange upstream of the stagnation point pushing the stagnation point—stable flow around to form a negative pressure zone—pressure gradient driving the mainstream," thus greatly improving energy utilization efficiency.

[0068] Comparison of flow field structures: such as Figure 7 and Figure 8 As shown, at a mass flow rate of 0.1385 kg / s and an angle of attack of 36°, and at a mass flow rate of 0.2 kg / s and an angle of attack of 38°, the airfoil of the comparative configuration exhibits significant boundary layer separation at the rear of the suction surface, with clearly identifiable separation vortex structures. In contrast, the airfoil of this application maintains a stable, body-hugging flow at the suction surface, with no obvious separation zone across the entire airfoil surface. This directly verifies that this application, through upstream injection at the stagnation point combined with an optimized inward-tilting discharge angle, can more effectively suppress flow separation at high angles of attack.

[0069] Pressure distribution comparison: such as Figure 9 As shown, at an angle of attack of 22° and a mass flow rate of 0.099 kg / s, the area of ​​the negative pressure concentration zone generated in the leading edge region by the device of this application is significantly larger than that of the comparative configuration, and the negative pressure zone is more concentratedly attached to the leading edge surface. This explains the physical mechanism of the superior lift-increasing and drag-reducing effect of this application from the perspective of pressure distribution: the upstream injection of the stagnation point, combined with the optimized inward discharge angle, causes the stagnation point position to shift downward, increases the curvature of the streamline at the leading edge of the suction front, enhances the acceleration effect, and stabilizes the injected gas to adhere around the flow, thereby forming a more concentrated and stronger leading edge negative pressure zone, which means a larger circulation increment and a stronger leading edge suction recovery.

[0070] This embodiment fully demonstrates that, under positive angle-of-attack conditions, this application, by placing the airflow injection component on the pressure surface and upstream of the free-flow stagnation point, and employing an optimized inward discharge angle, achieves a higher lift coefficient, a lower drag coefficient, and a greater stall angle-of-attack retardation at the same mass flow rate. Furthermore, the jet momentum characteristic value of the injection component is lower than that of the comparative configuration, resulting in higher energy utilization efficiency. This application provides an efficient and reliable lift enhancement technology solution for aircraft with stringent requirements for low-speed, high-lift performance, such as short takeoff and landing (STOL) aircraft and high-altitude long-endurance UAVs.

[0071] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A high-efficiency lift-enhancing flow control device suitable for thick airfoils, wherein the maximum relative thickness of the thick airfoil is in the range of 12% to 30%, characterized in that, include: The airfoil body has a leading edge endpoint, a trailing edge endpoint, a suction surface, and a pressure surface. Under positive angle of attack conditions, the leading edge region of the airfoil body has an incoming flow stagnation point located on the pressure surface. The airflow injection component is located on the pressure surface of the airfoil body, and under positive angle of attack conditions, it is located upstream of the free flow stagnation point and on the pressure surface arc segment between the leading edge endpoint and the stagnation point; An airflow recovery component is provided in the trailing edge region of the suction surface of the airfoil body; A circulating drive component is built inside the airfoil body. Its air intake port is connected to the airflow recovery component, and its exhaust port is connected to the airflow injection component. When the circulating drive component is running, it extracts the low momentum boundary layer fluid from the rear section of the suction surface from the airflow recovery component, pressurizes it, and discharges it from the airflow injection component. The mass flow rate of the discharged gas is equal to the mass flow rate of the extracted gas. The discharge direction of the airflow injection component forms an angle pointing inward between the local tangent direction of the pressure surface at the opening and the airfoil, and the value of the angle is 0° to 5°. Under positive angle of attack conditions, the pressurized gas discharged from the airflow injection component adheres to the leading edge surface of the airfoil body based on the wall adhesion effect and flows around to the suction surface, forming a negative pressure concentration area in the leading edge region, which can delay the airfoil's stall critical angle of attack and increase the maximum lift coefficient.

2. The high-efficiency lift-enhancing flow control device according to claim 1, characterized in that, The airfoil body is NACA0025, NACA0024, or NACA0021.

3. The high-efficiency lifting flow control device according to claim 1, characterized in that, The angle between the discharge direction of the airflow injection component and the local tangent direction of the pressure surface is 2° to 4°.

4. The high-efficiency lift-enhancing flow control device according to claim 1, characterized in that, The circulating drive component includes at least one of a micro-compressor, an electric booster rotor, or a positive displacement air pump, and its rated output capacity meets the requirements for providing the required gas circulation mass flow rate during takeoff and landing.

5. The high-efficiency lift-enhancing flow control device according to claim 1, characterized in that, It also includes a control unit, which adjusts the operating power of the cyclic drive component based at least on the current airfoil angle of attack and flight phase instructions, so as to minimize the total energy consumption of the system while keeping the drag coefficient non-positive.

6. A lift enhancement system for a short takeoff and landing (STOVL) aircraft, characterized in that, It includes the high-efficiency lift flow control device as described in any one of claims 1 to 5.

7. A low-speed aircraft, characterized in that, It includes the short takeoff and landing aircraft lift enhancement system as described in claim 6.

8. A flow control method for thick airfoils, applied to airfoils with a maximum relative thickness in the range of 12% to 30%, characterized in that, include: On the pressure surface of the airfoil, and at a position upstream of the free flow stagnation point under positive angle of attack conditions, pressurized gas is discharged in a direction with an inward inclination angle of 0° to 5° with the local tangent direction of the pressure surface; By utilizing the wall adhesion effect in the leading edge region of the airfoil, the pressurized gas flows stably around the leading edge to the suction surface, and a concentrated negative pressure zone is generated in the leading edge region. Meanwhile, at the trailing edge of the airfoil suction surface, low momentum boundary layer fluid near the wall is extracted, and the mass flow rate of the discharged gas is kept equal to the mass flow rate of the extracted gas. During takeoff and landing, the intensity of the negative pressure zone is controlled by controlling the mass flow rate of the gas circulation, thereby achieving increased lift, reduced drag, or thrust generation.

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