Open fan full range operating characteristic expansion method based on skeleton characteristics

Abstract

The application is an open fan full-range working characteristic expansion method based on skeleton characteristics, belonging to the field of open rotor engine; the method introduces a skeleton characteristic representation system with loss coefficient as the core to solve the problem that the efficiency in the representation of traditional propeller characteristics has singular points in the autorotation state, leading to the collapse of cross-condition numerical simulation calculation. By defining the work coefficient, pressure coefficient and loss coefficient, and based on the blade element theory to determine the ridgeback point and its existence condition, the ridgeback characteristics describing the characteristic change law of ridgeback point and the non-ridgeback characteristics describing the deviation law of non-ridgeback point are constructed. Finally, by combining the ridgeback characteristics and the non-ridgeback characteristics, the known local working condition characteristic data is continuously and smoothly expanded to the full working range including braking, autorotation and windmill state. The application fundamentally eliminates the numerical singular points in the characteristic curve, realizes the stable simulation and high-performance expansion of the open fan in the full working condition.

Description

Technical Field

[0001] This invention belongs to the field of open rotor engines, specifically relating to a method for extending the full-range operating characteristics of an open fan based on its frame characteristics. Background Technology

[0002] Open-fan propellers, as an advanced propulsion system between traditional propellers and turbofan engines, combine the low fuel consumption of turboprop engines with the high flight speed potential of turbofan engines, making them a key development direction for next-generation high-bypass propulsion systems. Since the 1970s, research institutions in the United States, Europe, and other countries have demonstrated through extensive wind tunnel tests and prototype verification that open-fan propellers can maintain a propulsion efficiency of over 80% at a cruise Mach number of 0.8, achieving fuel savings of 15%–40% compared to traditional turbofan engines. In recent years, with increasing global pressure to reduce aviation emissions and the need to upgrade narrow-body passenger aircraft, open-fan technology has once again become a focus of attention for aviation giants such as Boeing and Airbus.

[0003] Currently, the aerodynamic characteristics of open-type fans still follow the traditional propeller representation method, that is, using the advance ratio and pitch angle as independent variables, and the thrust coefficient and power coefficient as dependent variables, and further deriving the propulsion efficiency. This method is based on blade element momentum theory and has clear physical meaning and engineering applicability in normal forward propulsion conditions.

[0004] However, as the operating range of open fans expands to regions with high pitch ratios (such as braking, rotation, and windmill states), the traditional efficiency definition suffers from a mathematical singularity problem: at and near the rotation point, the efficiency tends to infinity or is indeterminate, causing numerical simulations to crash when switching between operating conditions, which severely limits the performance analysis of all operating conditions and the design of control systems.

[0005] Furthermore, traditional characteristic curves exhibit strong nonlinearity under non-design conditions, with sparse data that is difficult to extrapolate, posing significant challenges to the matching optimization of open fans, the design of stability control systems, and fault safety analysis.

[0006] Therefore, there is an urgent need for a method for representing and extending the characteristics of open fans that can eliminate mathematical singularities, maintain continuity across all operating conditions, and facilitate engineering expansion. Summary of the Invention

[0007] The technical problem to be solved: To overcome the shortcomings of existing technologies, this invention provides a method for extending the full-range operating characteristics of open fans based on skeleton characteristics. It proposes a "skeleton characteristic" representation method, using the loss coefficient as the core parameter to replace traditional propeller efficiency, eliminating the first type of singularity in the efficiency definition, and achieving a continuous and smooth representation of characteristics across the entire operating range from "forward state" to "windmill state". Simultaneously, it introduces ridge points and non-ridge characteristics to construct open fan skeleton characteristics similar to compressor characteristic curves, facilitating characteristic extension, data fitting, and engineering applications.

[0008] The technical solution of this invention is: a method for extending the full-range operating characteristics of an open fan based on frame characteristics, the specific steps of which are as follows: Step 1: Obtain conventional operating characteristic data of the target open fan at at least one set pitch angle, wherein the conventional operating characteristic data includes at least the pitch ratio. Tensile coefficient Power coefficient With efficiency ; Step 2: Based on the aforementioned traditional operating characteristic data, calculate and construct the frame characteristics of the open fan. The frame characteristics include at least the work coefficient characterizing the work-performing capacity. Pressure coefficient characterizing ideal isentropic work and the loss coefficient characterizing energy loss With advance ratio and propeller pitch angle The changing relationship; Step 3: Based on the calculated frame characteristics of the open fan, determine the ridge point in the frame characteristics of the open fan under each set pitch angle. The ridge point is the operating point with the minimum loss coefficient under a given pitch angle. Based on the ridge point, fit the relationship between the non-ridge point and the power coefficient offset.

[0009] Step 4: Based on the skeleton characteristics, by combining the spine characteristics and non-spine characteristics, the known operating characteristics of the open fan are extended from the design conditions to the full operating range including braking state, self-rotation state and windmill state, forming a continuous and non-singular full-range operating characteristic map.

[0010] A further technical solution of the present invention is: in step 2, the core parameters of the skeleton characteristics are defined as follows: Flow coefficient: ; Work coefficient: ; Pressure coefficient: ; Loss coefficient: ; In the formula, For flight speed, Physical rotational speed The diameter of the propeller. The input shaft power is the work done. The circumferential velocity at the tip of the propeller blades. For the speed of sound, Mach number, This is for the propeller shaft power.

[0011] A further technical solution of the present invention is: in step 3, the method for determining the spinal point includes: Based on the blade element theory, the relationship between the airfoil lift coefficient and the angle of attack is analyzed; Based on the condition that the loss coefficient is minimized at the spine point, the following is derived and solved: The existence condition of the spine point is to solve the following expression:

[0012] In the formula, This refers to the intake angle; This is the lift angle; This refers to the lift-to-drag ratio of the airfoil. Under the same flight conditions and similar aerodynamics, the airfoil lift-to-drag ratio... and , Irrelevant.

[0013] By combining traditional operating characteristic data, the approach ratio corresponding to the existence conditions at each pitch angle is determined. As the advance ratio of the spinal point.

[0014] A further technical solution of the present invention is: in step 3, the construction of the spinal characteristics includes: Plotting the advance ratio of the spine point pitch angle The curve of change; Plotting the spinal work coefficient pitch angle The curve of change; Plotting the spine point loss coefficient pitch angle The curve showing the change.

[0015] A further technical solution of the present invention is: in step 4, the method for constructing and expanding non-dorsal characteristics includes: For any given pitch angle Define the work coefficient offset of the spine point as ; The variation of the non-spine point loss coefficient was fitted using a quadratic polynomial. offset of the work coefficient of the spine point The changing relationship; Using logarithmic or polynomial functions to fit the advance ratio offset of the work coefficient of the spine point The relationship between changes in other relevant parameters; By changing This generates a complete non-back characteristic curve that deviates from the back point at that pitch angle. A further technical solution of the present invention is: the fitting relationship between the change in the loss coefficient and the offset of the work coefficient is:

[0016] In the formula, These are the fitting constants; The fitting relationship between the advance ratio and the power coefficient offset is as follows:

[0017] In the formula, , is the fitting constant.

[0018] A further technical solution of the present invention is: in step 4, a continuous and singular-free full-range operating characteristic spectrum is formed, specifically manifested as: the loss coefficient within the entire operating range... All values ​​are continuous and finite, thus avoiding the inefficiencies of traditional methods. The problem of singularities where values ​​tend to infinity near the state of rotation.

[0019] A further technical solution of the present invention is: the method further includes a characteristic conversion step, used to convert existing traditional propeller characteristic data into skeleton characteristic data, the specific process of which is as follows: a) Determine the approach ratio based on the given flight conditions. ; b) Determine different pitch angles The position of the lower back point is used to calculate the advance ratio of the back point. ; c) Calculate the work coefficient for each spinal point. Pressure coefficient and loss coefficient Thus, the spinal characteristics are obtained; d) Based on the spine characteristics, calculate the approach ratio of non-spine points for different pitch angles. and loss coefficient This yields non-dorsal characteristics; e) Combine back characteristics with non-back characteristics to complete the characteristic expansion towards a high advance ratio. A further technical solution of the present invention is that the full-range operating characteristic map generated by the method is used for at least one of the following aspects: aerodynamic design and performance optimization of open fans, engine / fan matching analysis, control law design of aircraft propulsion systems, and safety analysis and simulation under fault conditions, wherein the fault conditions include windmill conditions.

[0020] A system for extending the full-range operating characteristics of an open fan based on its frame characteristics, comprising: The data acquisition module is used to acquire conventional operating characteristic data of the target open fan at at least one set pitch angle, wherein the conventional operating characteristic data includes at least the pitch ratio. Tensile coefficient Power coefficient With efficiency ; The spine point determination module is connected to the data acquisition module and is used to determine the spine point in the open fan frame characteristics at each set pitch angle based on the traditional working characteristic data. The spine point is the operating point with the smallest loss coefficient at a given pitch angle. The skeleton characteristic construction module, connected to the spine point determination module, is used to calculate and construct the skeleton characteristics of the open fan based on the traditional operating characteristic data and the spine point. The skeleton characteristics include at least the power coefficient. Pressure coefficient and loss coefficient With advance ratio and propeller pitch angle The changing relationship; The full-condition extension module is connected to the skeleton characteristic construction module. Based on the skeleton characteristics, it extends the known operating characteristics of the open fan to the full operating range, including braking state, rotation state and windmill state, by combining spine characteristics and non-spine characteristics, and generates a continuous and singularity-free full-range operating characteristic map. Beneficial effects The beneficial effects of this invention are as follows: 1. This invention completely eliminates the numerical calculation collapse or divergence problem caused by the denominator approaching zero near the rotation state (efficiency singularity) by introducing a loss coefficient to replace the traditional efficiency as the core performance parameter. This makes it possible to perform full-condition, continuous dynamic simulation of the split-type fan from the forward state to the fan-wheel state, providing a stable and reliable mathematical model foundation for control law design, fault safety analysis, and real-time performance monitoring.

[0021] 2. The "skeleton characteristics" constructed in this invention (centered on the work coefficient, pressure coefficient, and loss coefficient) are smooth and continuous functions across the entire operating range. Combined with the extended framework of "spine characteristics" and "non-spine characteristics," it can accurately extrapolate and predict the characteristics of non-design conditions such as braking, rotation, and windmills based on limited experimental or high-fidelity simulation data (usually concentrated near the design point). This fills the data gap in the high advance ratio region of traditional characteristic maps, forming a complete and unified full-range operating characteristic database.

[0022] 3. The high-precision extension of characteristics achieved by this method can, to some extent, reduce the number of high-cost and high-risk wind tunnel tests or detailed CFD calculations required to obtain full-condition data, which helps to shorten the development cycle of open fans and even the entire propulsion system and reduce development costs.

[0023] In summary, this invention not only overcomes the key theoretical bottlenecks in the analysis of open fan characteristics, but also provides a set of efficient and practical engineering tools, which plays an important supporting role in accelerating the research and development and application of advanced propulsion technologies such as open rotor engines. Attached Figure Description

[0024] Figure 1 The diagram shows the operating characteristics of a certain type of conventional propeller published by NACA. Figure 2 A schematic diagram of a traditional propeller blade; Figure 3 This is a schematic diagram of the force analysis of a traditional propeller blade element; Figure 4 The operating characteristic curve of the propeller of an open fan; Figure 5 This is a schematic diagram showing the relationship between the power coefficient of the open fan of the present invention and the advance ratio and blade pitch. Figure 6 This is a schematic diagram showing the relationship between the pressure coefficient of the open fan of the present invention and the advance ratio and blade pitch. Figure 7 This is a schematic diagram showing the relationship between the loss coefficient of the open fan of the present invention and the feed ratio and pitch. Figure 8 This is a schematic diagram illustrating the frame characteristics of the open fan of the present invention; Figure 9 This is a schematic diagram illustrating the force analysis and velocity synthesis of the open fan blade profile of the present invention; Figure 10 This is a schematic diagram showing the relationship between the lift coefficient of the open fan blade and the angle of attack of the present invention; Figure 11 This is a schematic diagram illustrating the relationship between the ridge point advance ratio and the propeller pitch angle in an embodiment of the present invention. Figure 12This is a schematic diagram illustrating the relationship between the back point work coefficient and the propeller pitch angle in an embodiment of the present invention. Figure 13 This is a schematic diagram illustrating the relationship between the spine point loss coefficient and the pitch angle in an embodiment of the present invention. Figure 14 This is a schematic diagram illustrating the relationship between the change in non-spine point loss and the offset of the work coefficient in an embodiment of the present invention. Figure 15 This is a schematic diagram illustrating the relationship between the non-spine point advance ratio and the work coefficient in an embodiment of the present invention; Figure 16 This is a schematic diagram comparing the data of a certain type of open fan processed using the skeleton characteristics of the present invention with the original data. Detailed Implementation

[0025] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0026] Existing research has attempted to extend the characteristic curves by adding the Mach number dimension, employing higher-order fitting, or introducing empirical corrections (such as the airfoil optimization and CFD verification mentioned in CN120633293A), or by considering aerodynamic disturbance corrections under specific installation conditions (such as the angle of attack correction for wing-nacelle configurations in CN119622922B). However, none of these approaches have fundamentally solved the singularity problem and the challenge of continuity across all operating conditions in the characteristic representation. The following provides a detailed explanation: Typical operating conditions and general characteristics of open fans: 1. Traditional characteristic representation method for open fans Currently, the characteristics of open-type fans designed domestically adopt the traditional propeller characteristic representation method, that is, using power coefficient and thrust coefficient. Figure 1 The diagram shows the operating characteristics of a certain type of conventional propeller published by NACA.

[0027] The traditional method of representing the operating characteristics of propellers is derived from blade element theory. In blade element theory, the cross-section of the propeller, that is, the interface perpendicular to the span, is called the airfoil or blade element. The shape and size of the blade element have a direct impact on the propeller's operating performance.

[0028] A propeller consists of multiple blades, the radius of which is... The polygons of leaf element and leaf element velocity at the location of the blade are as follows: Figure 2 As shown in the figure. The angle of inclination between the blade element chord and the propeller's plane of rotation. Defined as the propeller blade element, the pitch angle is also known as the blade pitch.

[0029] The force situation of a leaf element can be obtained from its velocity polygon, such as... Figure 3As shown. The traditional method for representing the working characteristics of a propeller can be derived through force analysis of the propeller blade elements.

[0030] Let the blade element radius of the propeller be... r The width of the leaf element is b The radial increment is dr Its area is:

[0031] According to dynamic theory, the aerodynamic force acting on this leaf element is:

[0032]

[0033] In the formula, , , For the corresponding aerodynamic coefficients, air density, The velocity is the combined velocity of the airflow.

[0034] Bundle dR Projecting the force onto the axis of rotation and the plane of rotation, the tensile force acting on the leaf element can be obtained. and ,Right now:

[0035]

[0036] In the formula, To prevent the rise angle, .

[0037] The rotational torque and absorbed power of the leaf element are:

[0038]

[0039] In the formula, The rotational speed is 1000 rpm. Applying the above differential formula along the tip of the propeller ( ) to the root of the paddle ( Integrating, we obtain the number of blades as follows: The thrust and power of the propeller:

[0040]

[0041] Define the corresponding tensile coefficient and power coefficient The above formula can be expressed as:

[0042]

[0043] propeller efficiency Represented as:

[0044]

[0045] In the formula, The similarity criterion number is called the advance ratio. This refers to flight speed.

[0046] For traditional low-speed propellers, their thrust coefficient and power coefficient With advance ratio and propeller pitch angle hair Changes occur, that is, corresponding to Figure 1 The method for representing working characteristics.

[0047] Compared to traditional low-speed propellers, open-type fans extend the range of flight speeds, allowing them to operate at higher Mach numbers. However, the shock wave losses at high Mach numbers affect the operating characteristics of open-type fans. Therefore, the operating characteristics of open-type fans are currently typically expressed by adding a Mach number dimension to the traditional low-speed propeller operating characteristics, which is represented by the thrust coefficient. and power coefficient With advance ratio Pitch angle and flight Mach number The functional relationship.

[0048] 2. Analysis of the working status of open fans: Given a specific pitch, a more complete relationship between propeller power coefficient, thrust coefficient, and efficiency and the advance ratio is as follows: Figure 4 As shown.

[0049] As can be seen from the figure, the propeller's operating characteristics have the following two features: Given a fixed pitch and rotational speed, as the advance ratio increases, the propeller's thrust coefficient and power coefficient gradually decrease from their maximum values ​​at rest. When the advance ratio exceeds a certain value, both the propeller's thrust coefficient and power coefficient become negative.

[0050] The propeller efficiency initially increases with the increase of the forward ratio. However, once the maximum efficiency value is reached, further increases in the forward ratio actually decrease the efficiency.

[0051] Figure 4In the diagram, the points where the propeller thrust coefficient, power coefficient, and efficiency intersect the horizontal axis are marked as points A through D, in ascending order of the advance ratio. Based on the order of these four points, the six operating states of the propeller are defined as follows: Static tension state, corresponding to Figure 4 Point A, i.e., the propeller's forward ratio This operating state is equivalent to the maximum static thrust generated by the propeller on the ground, with the corresponding power coefficient at its maximum, but the effective power is zero.

[0052] Forward state, corresponding to Figure 4 In the AC interval, given a propeller pitch and rotational speed, thrust and power coefficient gradually decrease as the propeller advance ratio increases (flight speed increases). In the AB interval, propeller efficiency increases with increasing advance ratio. When the advance ratio increases to a certain value (point B), propeller efficiency reaches its maximum. In the subsequent BC interval, efficiency rapidly decreases with increasing advance ratio until it reaches zero at point C. For a given propeller pitch, the point of maximum efficiency corresponds to the propeller's optimal operating state.

[0053] The state of zero tension corresponds to Figure 4 Point C. When the propeller advance ratio reaches a certain value, the propeller's thrust coefficient is zero, and its efficiency is zero. In this operating state, the propeller generates neither thrust nor drag, but simply flies freely, cutting through the air. At this time, the propeller's power is greater than zero, and its power is only used to overcome the rotational drag torque.

[0054] Braking state, corresponding to Figure 4 In the CD range, the propeller's power coefficient is greater than zero, while its thrust coefficient and efficiency drop into negative territory. Under these conditions, the propeller is in a braking state, generating drag instead of thrust, much like a mixer in operation.

[0055] The rotation state corresponds to Figure 4 Point D. In this operating state, the propeller rotates not because it absorbs power from the engine, but because it is driven by the aerodynamic forces acting on it. In this operating state, the engine still needs to output a small amount of power to overcome various frictional forces and its own resistance, but the engine shaft output power is zero.

[0056] The windmill state corresponds to Figure 4 The interval after point D. In this operating state, the propeller not only does not require engine output power for rotation, but the propeller itself can also obtain energy from the high-speed airflow and drive the engine rotor to rotate.

[0057] To address the problems of existing technologies, this invention proposes a method for extending the full-range operating characteristics of open fans based on skeleton characteristics. The specific steps are as follows: Step 1: Obtain conventional operating characteristic data of the target open fan at at least one set pitch angle, wherein the conventional operating characteristic data includes at least the pitch ratio. Tensile coefficient Power coefficient With efficiency ; Step 2: Based on the aforementioned traditional operating characteristic data, calculate and construct the frame characteristics of the open fan. The frame characteristics include at least the work coefficient characterizing the work-performing capacity. Pressure coefficient characterizing ideal isentropic work and the loss coefficient characterizing energy loss With advance ratio and propeller pitch angle The changing relationship; Step 3: Based on the calculated frame characteristics of the open fan, determine the ridge point in the frame characteristics of the open fan under each set pitch angle. The ridge point is the operating point with the minimum loss coefficient under a given pitch angle. Based on the ridge point, fit the relationship between the non-ridge point and the power coefficient offset.

[0058] Step 4: Based on the skeleton characteristics, by combining the spine characteristics and non-spine characteristics, the known operating characteristics of the open fan are extended from the design conditions to the full operating range including braking state, self-rotation state and windmill state, forming a continuous and non-singular full-range operating characteristic map.

[0059] The above technical solution will be further analyzed below with reference to the accompanying drawings and examples: In one embodiment, the specific process of a method for extending the full-range operating characteristics of an open fan based on skeleton characteristics is as follows: 1. Parameter definition of open fan frame characteristics: Reference Figure 4 The given propeller operating characteristic curves show that during the transition from the forward state to the windmill state, and vice versa, the efficiency inevitably crosses the singularity at point D, causing the numerical simulation of the corresponding transition process to crash. The reason for this is that the propeller efficiency is defined as a ratio, resulting in a first-type singularity. This first-type singularity can be eliminated by redefining the propeller operating characteristics. Based on the above analysis, and referring to the representation method of compressor frame characteristics, the following representation method for the frame characteristics of an open fan is introduced.

[0060] Flow coefficient:

[0061] Work coefficient:

[0062] Pressure (isoentropic work) coefficient:

[0063] Loss coefficient:

[0064] In the formula, For flight speed, Physical rotational speed The diameter of the propeller. The input shaft power is the work done. The circumferential velocity at the tip of the propeller blades. For the speed of sound, Mach number, This is for the propeller shaft power.

[0065] Reference Figure 5 The relationship between the power coefficient of an open fan and the advance ratio and blade pitch is given. (Refer to...) Figure 6 The relationship between the pressure coefficient of an open fan and the advance ratio and pitch is given. Specifically, under static thrust conditions, we have: ， In the state of zero tension, we have: ， .

[0066] Reference Figure 7 The relationship between the power loss coefficient of an open-type fan and the advance ratio and pitch is presented. Because the definition uses the difference between the power coefficient and the pressure coefficient, the power loss coefficient of the open-type fan is a finite value under all operating conditions, avoiding the singularity of propeller efficiency and the infinity of values ​​on either side of the singularity. In other words, by adopting the definition of the power loss coefficient, the first type of singularity present in the traditional definition of propeller efficiency is eliminated.

[0067] At a given pitch angle Under these conditions, the relationships between the power coefficient, pressure coefficient, and loss coefficient in the open fan frame characteristics and the feed ratio are as follows: Figure 8 As shown. Compare the methods for representing the frame characteristics of open fans ( Figure 8 ) and traditional methods of representing propeller characteristics ( Figure 4 The advantages of using frame characteristics to describe the characteristics of open fans are as follows: Compared to efficiency loss coefficient Under static tension, the loss can be described as a function of physical rotation speed. The changes.

[0068] The efficiency representation has a singularity near the self-rotation state, while the loss coefficient is continuous in all operating states.

[0069] Using the skeleton properties can extend known propeller properties, and can also extend propeller properties in the forward state to the braking state and windmill state.

[0070] 2. Representation methods for skeleton characteristics: Reference Figure 8 The characteristics of the open fan frame show that the loss coefficient has a minimum value at a certain approach ratio. This minimum loss coefficient point is defined as the pitch angle. The spine point of an open-type fan is typically located to the right of its highest efficiency point. By plotting the power coefficient, pressure coefficient, and loss coefficient of the open-type fan's spine point as a function of the pitch angle, the spine characteristics of the open-type fan can be obtained.

[0071] Points on either side of the minimum loss point are defined as non-ridge points. The loss coefficient of a non-ridge point changes with the degree of deviation from the ridge point; that is, the farther the deviation from the ridge point, the greater the loss. The distance of the non-ridge point from the ridge point is still expressed as the pitch ratio. In the open fan frame characteristics, the pitch ratio corresponds to the flow coefficient in the compressor frame characteristics. The relationship between the work coefficient and loss coefficient of the non-ridge point and the pitch angle and pitch ratio is defined as the non-ridge characteristics.

[0072] The spine characteristics and non-spine characteristics together constitute the method for representing the skeleton characteristics of an open fan.

[0073] 3. Conditions for the existence of the spinal point: In describing the characteristics of an open fan frame, the ridge point is a crucial definition. It defines the point of minimum loss under a given pitch angle. Therefore, determining the existence condition of the ridge point for each pitch angle is the primary issue in describing the characteristics of an open fan frame. Here, the existence condition of the ridge point is presented by analyzing the lift characteristics of the airfoil.

[0074] Figure 9 The force analysis and velocity synthesis of an open fan blade profile are presented. (See figure.) For flight speed, For circumferential velocity, To induce velocity, The relative velocity of the three components is the resultant velocity. Indicates lift; This represents the component of lift in the direction of flight speed, i.e., the thrust of an open fan; This represents the component of lift in the direction of circumferential velocity, i.e., the circumferential drag of an open fan. The angle between the chord line and the leaf shape is the angle of attack. As the approach ratio increases from zero, the angle of attack changes from positive to negative. At a large positive angle of attack, stall occurs on the suction surface of the airfoil, corresponding to... Figure 10 To the right of the maximum lift coefficient of the mid-blade type; when the negative angle of attack is large, stall occurs on the pressure surface of the blade, corresponding to... Figure 10 The leftmost point where the lift coefficient of the mid-blade is maximized. The loss coefficient is larger during blade element stall. When the positive angle of attack is appropriate, airflow separation does not occur, and blade loss is smaller. The spine point is located precisely at... Figure 10 The operating point with the least loss within a certain angle of attack range to the left of the maximum lift coefficient of the mid-blade type.

[0075] According to the lift theory of airfoils, the effective power of an airfoil is:

[0076] In the formula, Indicates effective power.

[0077] The blade absorption power (blade element torque power) is:

[0078] In the formula, Indicates the absorbed power. Indicates the blade profile torque. Indicates rotational speed.

[0079] The commonly used aerodynamic efficiency of airfoils is expressed as:

[0080] In the formula, θ 0 represents the intake angle, and γ represents the lift-drag angle.

[0081] The blade loss coefficient used in the characteristics of open fan frames is defined as follows:

[0082] In the formula, Represent a constant, in In ratio operations, it is simplified, therefore in The difference must be expressed in the calculation. Under the same flight conditions and similar aerodynamics, this is a constant. and , Irrelevant.

[0083] Will right Differentiating, we get:

[0084] make:

[0085] The conditions for the existence of minimum loss at the spine point are as follows:

[0086] Because of the lift angle at the spine point It is always positive, therefore:

[0087] Therefore, the existence condition for the minimum loss at the spine point is:

[0088] This condition can be obtained by considering the relationship between the lift-to-drag ratio and angle of attack of the open fan blade profile. Clearly, the spine point is located to the left of the point of maximum lift on the lift curve. Therefore, the position of the spine point in the open fan frame characteristics at a given pitch can be determined based on this condition.

[0089] 4. Representation and expansion of spinal characteristics: The spine characteristics of an open-type fan consist of three curves: Back point advance ratio (flow coefficient) pitch angle The changing relationship.

[0090] Back point work coefficient pitch angle The changing relationship.

[0091] Back point loss coefficient pitch angle The changing relationship.

[0092] First, we analyze the relationship between the advance ratio at the spine point and the pitch angle. At a given pitch angle, there exists a unique spine point. Since the angle of attack of the spine point varies very little across different pitch angles, we can approximate the angle of attack of the spine point as... It remains unchanged. Thus, the relative airflow angle at the ridge point... Then, with the pitch angle The relative airflow angle continues to increase. The larger the ratio, the greater the advance distance. The larger the [spinal point advance ratio], the greater the [advance ratio]. With pitch angle Increases with the increase, such as Figure 11 As shown.

[0093] Reference Figure 12 The relationship between the spine point power coefficient of an open fan and the pitch angle is given. Increase, circumferential drag component Increasing the size of the spine increases the absorption power at the dorsal point, such as Figure 12 As shown; airfoil lift axial tensile component The reduction in power at the spine point decreases, ultimately leading to increased losses at the spine point, such as... Figure 13 As shown.

[0094] For spinal characteristics outside the experimental data range, the variation trend of spinal characteristic parameters analyzed above can be combined with existing data and fitted curves to expand the range.

[0095] 5. Representation and extension of non-dorsal characteristics: Non-back characteristics are studied at a certain pitch angle. Below, approach ratio J Deviation from the spine point advance ratio At that time, the advance ratio offset of work coefficient Change relationship and loss coefficient offset of work coefficient The changing relationship.

[0096] Based on the above analysis, with the lead-in ratio The increase of the loss coefficient First decrease, then increase; advance ratio at the spine point At that time, the spinal point loss coefficient Minimum. A quadratic polynomial is used to fit the change in loss at non-spine points. Offset of spinal work coefficient The relationships of change are as follows:

[0097] In the formula, Let be a constant. This relationship can be expressed as: Figure 14 The curve. This relationship will change accordingly for different pitch angles.

[0098] Power coefficient Work coefficient at the back Nearby, especially when At this time, the approach ratio decreases as the power factor increases. The non-spine point approach ratio is defined as follows. Relative spinal work coefficient Change Logarithmic curve fitting was used to fit the advance ratio. Variation with coefficient The relationship between the changes is as follows:

[0099] In the formula, , Let be a constant. This relationship can be expressed as: Figure 15 The curve. This relationship will change accordingly for different pitch angles.

[0100] 6. Open Fan Frame Characteristic Conversion and Expansion Process Based on the above representation method of open fan frame characteristics, the propeller characteristics represented by traditional methods can be transformed and extended. The specific process is as follows: According to flight conditions ( 、 、 Determine the advance ratio .

[0101] Determine different pitch angles according to the method in the condition for the existence of the spine point. β Calculate the advance ratio based on the location of the spine point. .

[0102] Calculate different pitch angles based on the spine characteristic representation and extended method. Work coefficient of the spine point and loss coefficient Draw the characteristics of the spine.

[0103] Given pitch angle Select the work coefficient offset Calculate the corresponding approach ratio and change in loss Plot the non-spine characteristics for a given pitch angle.

[0104] Select different pitch angles and repeat the above steps to plot all non-spine characteristics.

[0105] Reference Figure 16 As shown, the data of a certain type of open fan processed using skeleton characteristics is compared with the original data.

[0106] When the propeller efficiency is greater than 70%, the back-calculation error between efficiency and thrust coefficient does not exceed 1%; when the efficiency is between 60% and 70%, the error does not exceed 3%. When the efficiency is below 60%, the back-calculation error gradually increases. The back-calculation error of the thrust coefficient does not exceed 0.1% across the entire operating range. These data indicate that the back-calculation results of the spine characteristic method agree well with the original experimental data, and the obtained back-calculation data has high reliability, demonstrating that this method can reliably characterize the propeller's performance characteristics across the entire operating range.

[0107] 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 method for extending the full-range operating characteristics of an open fan based on skeleton characteristics, characterized in that, The specific steps are as follows: Step 1: Obtain conventional operating characteristic data of the target open fan at at least one set pitch angle, wherein the conventional operating characteristic data includes at least the pitch ratio. Tensile coefficient Power coefficient With efficiency ; Step 2: Based on the aforementioned traditional operating characteristic data, calculate and construct the frame characteristics of the open fan. The frame characteristics include at least the work coefficient characterizing the work-performing capacity. Pressure coefficient characterizing ideal isentropic work and the loss coefficient characterizing energy loss With advance ratio and propeller pitch angle The changing relationship; Step 3: Based on the calculated skeleton characteristics of the open fan, determine the spine point in the skeleton characteristics of the open fan under each set pitch angle. The spine point is the operating point with the minimum loss coefficient under a given pitch angle. Fit the relationship between the non-spine point and the power coefficient offset based on the spine point. Step 4: Based on the skeleton characteristics, by combining the spine characteristics and non-spine characteristics, the known operating characteristics of the open fan are extended from the design conditions to the full operating range including braking state, self-rotation state and windmill state, forming a continuous and non-singular full-range operating characteristic map.

2. The method for extending the full-range operating characteristics of an open fan based on skeleton characteristics according to claim 1, characterized in that: In step 2, the core parameters of the skeleton characteristics are defined as follows: Flow coefficient: ; Work coefficient: ; Pressure coefficient: ; Loss coefficient: ; In the formula, For flight speed, Physical rotational speed The diameter of the propeller. The input shaft power is the work done. The circumferential velocity at the tip of the propeller blades. For the speed of sound, Mach number, This is for the propeller shaft power.

3. The method for extending the full-range operating characteristics of an open fan based on skeleton characteristics according to claim 2, characterized in that: In step 3, the method for determining the spinal point includes: Based on the blade element theory, the relationship between the airfoil lift coefficient and the angle of attack is analyzed; Based on the condition that the loss coefficient is minimized at the spine point, the following is derived and solved: The existence condition of the spine point is to solve the following expression: In the formula, This refers to the intake angle; This is the lift angle; Indicates the lift-to-drag ratio of the airfoil; By combining traditional operating characteristic data, the approach ratio corresponding to the existence conditions at each pitch angle is determined. As the advance ratio of the spinal point.

4. The method for extending the full-range operating characteristics of an open fan based on skeleton characteristics according to claim 3, characterized in that: In step 3, the construction of spinal characteristics includes: Plotting the advance ratio of the spine point pitch angle The curve of change; Plotting the spinal work coefficient pitch angle The curve of change; Plotting the spine point loss coefficient pitch angle The curve showing the change.

5. The method for extending the full-range operating characteristics of an open fan based on skeleton characteristics according to claim 4, characterized in that: In step 4, the methods for constructing and expanding non-dorsal characteristics include: For any given pitch angle Define the work coefficient offset of the spine point as ; The variation of the non-spine point loss coefficient was fitted using a quadratic polynomial. offset of the work coefficient of the spine point The changing relationship; The advance ratio is fitted with a logarithmic or polynomial function to measure the shift in the work coefficient of the spine point. The relationship between changes in other relevant parameters; By changing This generates a complete non-back characteristic curve that deviates from the back point at that pitch angle.

6. The method for extending the full-range operating characteristics of an open fan based on skeleton characteristics according to claim 5, characterized in that: The fitting relationship between the change in the loss coefficient and the offset of the work coefficient is as follows: In the formula, These are the fitting constants; The fitting relationship between the advance ratio and the power coefficient offset is as follows: In the formula, , is the fitting constant.

7. The method for extending the full-range operating characteristics of an open fan based on skeleton characteristics according to claim 6, characterized in that: In step 4, a continuous and singular-free full-range operating characteristic map is formed, specifically manifested as: the loss coefficient across the entire operating range. All values ​​are continuous and finite, thus avoiding the inefficiencies of traditional methods. The problem of singularities where values ​​tend to infinity near the state of rotation.

8. The method for extending the full-range operating characteristics of an open fan based on skeleton characteristics according to claim 7, characterized in that: The method also includes a characteristic conversion step, used to convert existing traditional propeller characteristic data into skeleton characteristic data. The specific process is as follows: a) Determine the approach ratio based on the given flight conditions. ; b) Determine different pitch angles The position of the lower back point is used to calculate the advance ratio of the back point. ; c) Calculate the work coefficient for each spinal point. Pressure coefficient and loss coefficient Thus, the spinal characteristics are obtained; d) Based on the spine characteristics, calculate the approach ratio of non-spine points for different pitch angles. and loss coefficient This yields non-dorsal characteristics; e) Combine back characteristics with non-back characteristics to complete the characteristic expansion towards a high advance ratio.

9. The method for extending the full-range operating characteristics of an open fan based on skeleton characteristics according to claim 8, characterized in that: The full-range operating characteristic map generated by the method is used for at least one of the following aspects: aerodynamic design and performance optimization of open fans, engine / fan matching analysis, control law design of aircraft propulsion systems, and safety analysis and simulation under fault conditions, including windmill conditions.

10. A system for extending the full-range operating characteristics of an open fan based on skeleton characteristics, used to execute the method for extending the full-range operating characteristics of an open fan based on skeleton characteristics as described in any one of claims 1-9; characterized in that, include: The data acquisition module is used to acquire conventional operating characteristic data of the target open fan at at least one set pitch angle, wherein the conventional operating characteristic data includes at least the pitch ratio. Tensile coefficient Power coefficient With efficiency ; The spine point determination module is connected to the data acquisition module and is used to determine the spine point in the open fan frame characteristics at each set pitch angle based on the traditional working characteristic data. The spine point is the operating point with the smallest loss coefficient at a given pitch angle. The skeleton characteristic construction module, connected to the spine point determination module, is used to calculate and construct the skeleton characteristics of the open fan based on the traditional operating characteristic data and the spine point. The skeleton characteristics include at least the power coefficient. Pressure coefficient and loss coefficient With advance ratio and propeller pitch angle The changing relationship; The full-condition extension module is connected to the skeleton characteristic construction module. Based on the skeleton characteristics, it extends the known operating characteristics of the open fan to the full operating range, including braking state, rotation state and windmill state, by combining spine characteristics and non-spine characteristics, and generates a continuous and singularity-free full-range operating characteristic map.

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