Test piece design method for turbofan engine supercharging stage surge

Abstract

The invention relates to a test piece design method for booster stage surge of a large-bypass-ratio double-rotor turbofan engine. The test piece design method comprises the following steps: acquiring a full-size fan booster stage streamline; determining a streamline lower limit; determining a target streamline; the streamline lower limit is compared with the target streamline, and the streamline adopted for fan topping of the large-bypass-ratio turbofan engine is determined; and according to the determined streamline, each part of the test piece is redesigned to form a new engine, so that surge can be realized only by adjusting the angle of the VBV, and the test result can truly and reasonably reflect the performance and surge margin of the booster stage.

Description

Technical Field

[0001] The present invention relates to the technical field of aeroengines, and a test piece design method for surging suppression of a booster stage of a high bypass ratio dual-rotor turbofan engine, which is mainly used for experimental verification of the surge margin of the booster stage. Background Art

[0002] A turbofan engine, abbreviated as a fan engine, refers to a turbojet engine in which the outlet air flow of a fan (or a low-pressure compressor) enters two ducts, namely an inner duct and an outer duct respectively. The fan (or the low-pressure compressor) of the turbofan engine compresses both the outer duct air and the inner duct air. The compressor that is coaxial with the fan of a high bypass ratio turbofan engine and compresses the inner duct air is called a booster stage.

[0003] Surge and stall are two typical aerodynamic unstable flow states in a compressor, which are phenomena seriously endangering the safe operation of the engine. The consequences brought about by surge and stall include engine flameout, structural failure, overheating or inability to recover thrust.

[0004] The characteristics of surge are that the pressure ratio of the engine compression component fluctuates greatly, the flow rate decreases significantly or reverse flow occurs. Surge will cause the air flow in the compression system to be interrupted and reverse, and it cannot be stably matched with the downstream components, thus entering an unstable state, which will further lead to damage of engine components, a significant increase in exhaust temperature or flameout and shutdown. The surge margin is a physical quantity characterizing the relative distance between the operating point of the compression component and the surge boundary. A smaller surge margin means that the operating point of the compression component is closer to the surge boundary. When the surge margin is 0 or negative, it means that the compression component will surge and cannot work properly.

[0005] Stall is manifested as the flow separation phenomenon occurring on one or more compressor blades, manifested as various forms of pressure disturbances, and will cause small or persistent fluctuations in the engine pressure and flow rate, resulting in deterioration of compression performance.

[0006] In order to maintain the aerodynamic stability of the engine within the entire flight envelope and ensure the comfort and safety of civil aviation, it is necessary to conduct surging suppression tests on the compression components of the engine, especially newly developed engines. How to conduct surging suppression tests on the booster stage components in the whole engine environment and ensure that the test results truly and reasonably reflect the performance and surge margin of the booster stage is particularly important.

[0007] During component testing of the booster stage, the backpressure valve on the exhaust volute or exhaust tower of the test bench is generally adjusted to reduce the flow rate of the booster stage, achieving the purpose of forcing surge. However, on the whole engine, the booster stage cannot be forced to surge through the backpressure valve. Instead, the bleed air volume of the VBV (variable bleed valve in the intermediate casing, which can increase the surge margin of the fan core / booster stage at partial speeds, and can also bleed air from the booster stage core and discharge foreign objects) is adjusted, or the area of the core nozzle is enlarged (the nozzle is a component that allows the gas / air to continue to expand and accelerate, converting the pressure energy into kinetic energy and spraying out at high speed. For a twin-duct turbofan engine, it is further divided into an "outer duct nozzle" and a "core nozzle") to raise the operating line of the booster stage.

[0008] At present, the bypass ratio of advanced civil turbofan engines is as high as 10 or more, that is, the flow rate of the fan is very large and the power consumption is very large. When the same core engine reaches a certain relative corrected speed, the low-pressure rotor speed is relatively low, that is, the operating line of the booster stage is relatively low. It is very difficult to achieve the purpose of forcing the booster stage to surge only by changing the bleed air volume of the VBV, or even by superimposing and enlarging the area of the core nozzle. Moreover, when the low-pressure rotor speed of a high-bypass ratio twin-rotor turbofan engine is relatively high, there will be risks of over-limiting the high-pressure rotor speed and the turbine inlet temperature, and it is impossible to conduct tests on the ground test bench.

[0009] Therefore, a method is needed that can achieve forced surge only by adjusting the angle of the VBV, and the test results can truly and reasonably reflect the performance and surge margin of the booster stage. Summary of the Invention

[0010] The summary of the invention is provided to introduce some concepts that will be further described in the following detailed description in a simplified form. The summary of the invention is not intended to identify the key features or essential features of the claimed subject matter; nor is it intended to be used to determine or limit the scope of the claimed subject matter.

[0011] The present invention provides a method. By topping the fan to reduce the power of the fan while retaining a part of the outer duct, the performance of the fan core is ensured not to be affected by topping. Since the air flow rate in the outer duct of the fan is greatly reduced and the low-pressure shaft load is reduced, the risks of over-limiting the high-pressure rotor speed and the turbine inlet temperature can be avoided. At the same time, since the mass of the fan blades is reduced, the load on the fan disk is also reduced, and the safety risk of the test is reduced. The operating line of the booster stage on the whole engine is raised, and forced surge can be achieved only by adjusting the angle of the VBV, and the test results can truly and reasonably reflect the performance and surge margin of the booster stage. It is ensured that the engine can record the complete characteristics of the booster stage within the full flight envelope at the ground state, including the speed characteristics and the surge boundary.

[0012] A design method for a test piece for surging prevention in the booster stage of a high-bypass-ratio dual-rotor turbofan engine according to the present invention includes: obtaining the streamline of the full-scale fan booster stage; determining the lower limit of the streamline; determining the target streamline; comparing the lower limit of the streamline with the target streamline to determine the streamline adopted for the fan tip cutting of the high-bypass-ratio turbofan engine; and redesigning each component of the test piece according to the determined streamline. Among them:

[0013] Obtaining the streamline of the full-scale fan booster stage includes: setting the initial bypass ratio and obtaining a set of streamlines according to the design results of the fan booster stage.

[0014] Determining the lower limit of the streamline includes: setting the bypass ratio and setting the initial value of the bypass ratio to 1.0;

[0015] Taking the streamline corresponding to the set bypass ratio as the casing, cutting the tops of the fan blades and OGV blades, and only retaining the part below the streamline; carrying out CFD calculations. When calculating the core / outer flow characteristics, keep the back pressure of the outer flow / core flow at the same speed consistent with that of the full-scale fan booster stage; and judging whether the streamline can simulate the function of the fan outer flow. If the streamline cannot simulate the function of the fan outer flow, or the core flow characteristics of the fan are inconsistent with the original core flow characteristics of the fan, then return to the step of setting the bypass ratio, increase the bypass ratio by 0.5, and repeat the above steps until the streamline can simulate the function of the fan outer flow and the core flow characteristics of the fan are not affected, and determine the current streamline as the lower limit of the streamline.

[0016] Determining the target streamline includes: setting the bypass ratio and setting the initial value of the bypass ratio to 0.5;

[0017] Taking the streamline corresponding to the set bypass ratio as the casing, cutting the tops of the fan blades and OGV blades, and only retaining the part below the streamline; carrying out CFD calculations, and carrying out overall engine performance calculations based on the calculation results to determine the operating line of the fan core / booster stage. When calculating the core / outer flow characteristics, keep the back pressure of the outer flow / core flow at the same speed consistent with that of the full-scale fan booster stage, including by giving the characteristics of each component, calculating the flow rate and pressure ratio of each component of the engine under certain rotational speed and inlet atmospheric conditions, and obtaining the operating line of the fan core / booster stage by calculating the flow rate and pressure ratio under the same inlet atmospheric conditions at different rotational speeds. The VBV bleed is not considered in the calculation process; and judging whether all operating lines are higher than the surge boundary line. If the operating line is lower than the surge boundary line at any rotational speed, then return to the step of setting the bypass ratio, reduce the bypass ratio by 0.5, and repeat the above steps until the operating line of the fan core /

[0018] booster stage is higher than the surge boundary line at all rotational speeds, and determine the current streamline as the target streamline.

[0019] Comparing the lower limit of the streamline with the target streamline to determine the streamline adopted for the fan tip cutting of a high-bypass ratio turbofan engine includes: when the target streamline is higher than the lower limit of the streamline, the target streamline is adopted; when the target streamline is lower than the lower limit of the streamline, the lower limit of the streamline is adopted.

[0020] Redesigning each component of the test piece according to the determined streamline includes: redesigning the fan,

[0021] the OGV blades and the nacelle to form a new engine.

[0022] These and other features and advantages will become apparent by reading the following detailed description and referring to the associated drawings. It should be understood that the foregoing general description and the following detailed description are illustrative only and do not limit the various aspects claimed. Brief Description of the Drawings

[0023] The present invention will be described in more detail below by reference to specific embodiments shown in the accompanying drawings.

[0024] Figure 1 is a flowchart of the test piece design method of the present invention;

[0025] Figure 2 is a schematic diagram of the flow path of a high-bypass ratio turbofan engine;

[0026] Figure 3 is a schematic diagram of the design result of the fan booster stage;

[0027] Figure 4 is a schematic diagram of the tip cutting range;

[0028] Figure 5 is a schematic diagram of the limit streamline of the fan rotor suction surface;

[0029] Figure 6 is a schematic diagram of the flow rate - efficiency characteristic. Detailed Description of the Embodiments

[0030] The present invention will be described in more detail below by reference to specific embodiments shown in the accompanying drawings. By reading the detailed description of the following specific embodiments, various advantages and benefits of the present invention will become clear to those of ordinary skill in the art. However, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. The following embodiments are provided to enable a more thorough understanding of the present invention. Unless otherwise specified, the technical terms or scientific terms used in this application should have the ordinary meaning understood by those skilled in the art to which this application belongs.

[0031] The present invention truncates the fan, retaining a part of the bypass duct, thereby significantly reducing the input power of the fan. The minimum bypass ratio should be such that the remaining bypass duct (including the bypass nozzle) can simulate the bypass duct of the fan, ensuring that the characteristics of the fan core are not affected, and further ensuring the verification effect of the matching between the fan core and the booster stage. The maximum bypass ratio should be such that when the VBV is fully closed within the full rotational speed range, choking can be achieved through the VBV, and the rotational speed of the low-pressure rotor can reach the highest rotational speed of the entire envelope.

[0032] The following explains the test piece design method of the present invention with reference to the accompanying drawings.

[0033] Figure 1 is the flow chart of the test piece design method of the present invention.

[0034] First, in step S10, the full-scale fan booster stage streamline is obtained.

[0035] The flow path of a high bypass ratio turbofan engine is as Figure 2 shown, where 1 is the fan. After the air flow passes through the fan, it is divided into two bypass ducts. The bypass duct is discharged through the OGV vane 3 and the bypass nozzle 7, and the core flow passes through the booster stage 2 into the core engine 5 and is discharged through the low-pressure turbine 6 and the core nozzle 8. Assume the initial bypass ratio is A. According to the design results of the fan booster stage components (including the bypass nozzle), a set of streamlines is obtained, as Figure 3 shown.

[0036] Next, in step S20, the Figure 4 shown streamline lower limit 9 is determined. The steps S20 for determining the streamline lower limit include the following sub-steps:

[0037] · In step S21, the bypass ratio is set, and the initial bypass ratio A is set to 1.0;

[0038] · In step S22, the streamline corresponding to this bypass ratio is used as the casing, and the fan blade 1 and the OGV vane 3 are truncated, only retaining the part below the streamline;

[0039] · In step S23, CFD calculations are carried out: when calculating the core / bypass duct characteristics, the back pressure of the bypass duct / core flow at the same rotational speed is kept consistent with that of the full-scale fan booster stage;

[0040] · In step S24, it is judged whether the streamline can simulate the function of the fan bypass duct: If the flow field is similar as Figure 5 shown, ( Figure 5 shows the limit streamline diagram of the suction surface of the fan rotor, where (a) is that of the full-scale fan,

[0041] (b) is for the tip-cut fan. The remaining outer annulus (including the outer annulus nozzle) can simulate the function of the fan outer annulus, and the mass flow - pressure ratio characteristic of the fan inner annulus is not affected. Determine that this streamline is the lower limit streamline 9. If the streamline cannot simulate the function of the fan outer annulus, or the characteristics of the fan inner annulus are inconsistent with the original fan inner annulus characteristics, then increase the bypass ratio by 0.5, and the process returns to step S21, repeating each sub-step of the above process until the streamline can simulate the function of the fan outer annulus and the characteristics of the fan inner annulus are not affected.

[0042] Next, in step S30, determine Figure 4 the target streamline 10 as shown. The steps to determine the target streamline include the following sub-steps:

[0043] · In step S31, set the bypass ratio, and the initial bypass ratio A is 0.5;

[0044] · In step S32, use the streamline corresponding to this bypass ratio as the casing, and perform tip-cut on the fan blade 1 and the OGV blade 3, only retaining the part below the streamline.

[0045] · In step S33, conduct CFD calculations. When calculating the inner annulus / outer annulus characteristics, keep the back pressure of the outer annulus / inner annulus at the same rotational speed consistent with that of the full-scale fan booster stage. Based on the calculation results of the tip-cut fan booster stage, conduct overall engine performance calculations to determine the working line of the fan inner annulus / booster stage (VBV fully closed). That is, based on the thermodynamic cycle calculation software of the whole engine, by specifying the characteristics of each component (such as the fan inner annulus / booster stage), at a certain rotational speed and inlet atmospheric conditions, calculate the mass flow and pressure ratio of each component of the engine. By calculating the mass flow and pressure ratio at different rotational speeds under the same inlet atmospheric conditions, obtain the working line of the fan inner annulus / booster stage. The calculation process does not consider VBV bleeding.

[0046] · In step S34, determine whether all rotational speed working lines are higher than the surge boundary line. If the working line is higher than the surge boundary lines at all rotational speeds, set the current streamline as the target streamline; if the working line is lower than the surge boundary line at any rotational speed, then decrease the bypass ratio by 0.5, return to step S32, and repeat each sub-step of the above process until the working line of the fan inner annulus / booster stage is higher than the surge boundary lines at all rotational speeds ( Figure 6 ).

[0047] After steps S20 and S30 are completed, this method enters step S40 to determine the streamline adopted for the tip-cut of the fan of the high-bypass ratio turbofan engine. The specific method is to compare the lower limit streamline obtained in step S20 with the target streamline obtained in step S30. When the target streamline is higher than the lower limit streamline, adopt the target streamline; when the target streamline is lower than the lower limit streamline, adopt the lower limit streamline.

[0048] Finally, in step S50, according to the streamline determined in step S40, as the streamline inside the engine nacelle, components such as the fan 1, OGV vane 3, and nacelle 4 are redesigned and processed to form a new engine. On this new engine, the performance acquisition of the booster stage over the entire envelope and at all rotational speeds can be achieved only by adjusting the VBV bleed air volume.

[0049] The implementation of the present invention is simple. By cutting the top of the fan and redesigning the bypass duct, the operating line of the booster stage and the achievable low-pressure rotor speed are increased. Surge can be achieved only by adjusting the bleed volume of the VBV, and the performance and surge margin of the booster stage over the entire flight envelope and at all rotational speeds can be obtained. By retaining part of the bypass duct, the characteristics of the fan core are not affected, ensuring the matching between the fan core and the booster stage, so that the test results can truly reflect the performance and surge margin of the booster stage. In addition, since the weight of the fan blades is significantly reduced, it is beneficial to the strength design of the fan blades and the fan disk, improving the reliability of the test piece.

[0050] The above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit them; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the various embodiments of the present application, and they should all be covered by the scope of the claims and the description of the present application.

Claims

1. A design method for a test piece for surging prevention in the booster stage of a high bypass ratio dual-rotor turbofan engine, including: Obtaining the streamline of the full-scale fan booster stage; Determining the lower limit of the streamline; Determining the target streamline; Comparing the lower limit of the streamline with the target streamline to determine the streamline adopted for the fan tip cutting of the high bypass ratio turbofan engine; and Redesigning each component of the test piece according to the determined streamline.

2. The method according to claim 1, wherein, the obtaining of the streamline of the full-scale fan booster stage includes: Setting the initial bypass ratio, and obtaining a set of streamlines according to the design result of the fan booster stage.

3. The method according to claim 1, wherein, the determining of the lower limit of the streamline includes: Setting the bypass ratio; Taking the streamline corresponding to the set bypass ratio as the casing, cutting the tops of the fan blades and OGV blades, and only retaining the part below the streamline; Conducting CFD calculations; and Judging whether the streamline can simulate the function of the fan outer duct. If the streamline cannot simulate the function of the fan outer duct, or the fan inner duct characteristics are inconsistent with the original fan inner duct characteristics, then return to the step of setting the bypass ratio, increasing the bypass ratio, and repeating the above steps until the streamline can simulate the function of the fan outer duct and the fan inner duct characteristics are not affected, and determining the current streamline as the lower limit of the streamline.

4. The method according to claim 3, wherein, in the conducting of the CFD calculations, when calculating the inner duct / outer duct characteristics, keep the back pressure of the outer duct / inner duct at the same rotational speed consistent with that of the full-scale fan booster stage.

5. The method according to claim 3, wherein, the setting of the bypass ratio includes setting the initial value of the bypass ratio to 1.0, and the increasing of the bypass ratio includes increasing the bypass ratio by 0.

5.

6. The method according to claim 1, wherein, the determining of the target streamline includes: Setting the bypass ratio; Taking the streamline corresponding to the set bypass ratio as the casing, cutting the tops of the fan blades and OGV blades, and only retaining the part below the streamline; Conducting CFD calculations, and conducting overall engine performance calculations based on the calculation results to determine the working line of the fan inner duct / booster stage; and Judging whether all the working lines are higher than the surge boundary line. If the working line is lower than the surge boundary line at any rotational speed, then return to the step of setting the bypass ratio, decreasing the bypass ratio, and repeating the above steps until the working line of the fan inner duct / booster stage is higher than the surge boundary line at all rotational speeds, and determining the current streamline as the target streamline.

7. The method according to claim 6, wherein, the setting of the bypass ratio includes setting the initial value of the bypass ratio to 0.5, and the decreasing of the bypass ratio includes decreasing the bypass ratio by 0.

5.

8. The method according to claim 6, wherein, in the conducting of the CFD calculations, when calculating the inner duct / outer duct characteristics, keep the back pressure of the outer duct / inner duct at the same rotational speed consistent with that of the full-scale fan booster stage; and Based on the above results, the overall engine performance calculation to determine the operating line of the fan core / booster stage includes: by specifying the characteristics of each component, calculating the flow rate and pressure ratio of each engine component at a certain rotational speed and inlet atmospheric conditions, and obtaining the operating line of the fan core / booster stage by calculating the flow rate and pressure ratio at the same inlet atmospheric conditions for different rotational speeds. The VBV bleed is not considered in the calculation process.

9. The method according to claim 1, wherein, the streamline used to determine the fan tip cutting of the high bypass ratio turbofan engine by comparing the lower limit of the streamline with the target streamline includes: when the target streamline is higher than the lower limit of the streamline, using the target streamline; and when the target streamline is lower than the lower limit of the streamline, using the lower limit of the streamline.

10. The method according to claim 1, wherein, the redesign of each component of the test piece according to the determined streamline includes: redesigning the fan, OGV blades and nacelle to form a new engine.

Images