A method for determining the flight envelope of a turbofan engine

Abstract

The present application belongs to the field of engine design technology, and specifically relates to a method for determining the flight envelope of an aircraft turbofan engine. The method mainly includes: step S1, obtaining the load spectrum of the power extraction of aircraft accessories within the full envelope range and the comprehensive distortion index allowed by the engine inlet; step S2, determining the speed of the compression component of the turbofan engine when the engine stability margin is weakest; step S3, determining the stable working boundary of the engine after power extraction based on the speed of the compression component when the engine stability margin is weakest. The present application obtains the speed of the critical distortion index of the engine under different altitudes and different speed conditions through pressure distortion tests, thereby determining the flight envelope of the engine under the influence of actual power extraction, greatly improving the engine aerodynamic stability evaluation method, thereby giving the power extraction limit within the envelope range, and avoiding problems such as engine surge.

Description

Technical Field

[0001] The present application belongs to the field of engine design technology, and specifically relates to a method for determining the flight envelope of an aircraft turbofan engine under actual power extraction conditions. Background Art

[0002] During the aircraft engine design process, in addition to achieving high performance and reliability, aircraft serviceability specifications must also be met. This requires sufficient available stability margin throughout the entire flight envelope. Simply put, this involves comprehensively considering various requirements, such as high thrust, low fuel consumption, high reliability, low cost, and stability margin, to find the optimal balance based on the aircraft's operational requirements. Therefore, stability assessments are conducted throughout every stage of the aircraft engine development cycle. This involves studying the impact of various destabilizing factors on engine stability under specified flight conditions to avoid situations where the required stability margin due to each destabilizing factor exceeds the available stability margin. Therefore, the impact of each destabilizing factor on engine stability must be considered throughout the engine design process. With the advancement of technology, aircraft are increasingly demanding in-flight features and power extraction, which in turn has a greater impact on engine performance.

[0003] Currently, the aerodynamic stability assessment of aviation turbofan engines is often performed solely through inlet pressure distortion tests under ground conditions to obtain the engine's critical distortion index, calculate the residual margin of the engine's compression components, and thus evaluate the engine's aerodynamic stability. A few engines consider the impact of partial-state power extraction under ground conditions. However, during the installation and use of aviation turbofan engines, aircraft power extraction always exists, and the power extraction of aircraft accessories is an absolute value that does not change with altitude and indicated speed (such as the generator). However, the thrust generated by the engine (providing power extraction) will vary with changes in altitude and indicated speed. Therefore, the aircraft power extraction is not a fixed proportion of the engine's output power. When the proportion exceeds a certain value, it will have a significant impact on engine performance and aerodynamic stability, and surge may occur, resulting in a flight accident. Summary of the Invention

[0004] To solve the above problems, the present application provides a method for determining the flight envelope of a turbofan engine taking into account the actual power extraction of aircraft accessories, which mainly includes:

[0005] Step S1, obtaining the load spectrum of aircraft accessory power extraction within the full envelope and the comprehensive distortion index allowed for engine inlet;

[0006] Step S2, determining the converted speed of the compression component of the turbofan engine when the engine stability margin is weakest;

[0007] Step S3: Perform aerodynamic stability calculation of the compression component at typical altitude and speed points within the flight envelope, taking into account different aircraft power extraction conditions, to obtain the envelope altitude and speed at the converted speed state when the stability margin is weakest, thereby determining the theoretical calculation boundary of stable operation of the engine after power extraction.

[0008] Preferably, step S3 further comprises:

[0009] Step S31, calculating the stability margin of the compression component corresponding to the indicated airspeed at the left boundary of a certain altitude within the flight envelope;

[0010] Step S32: After increasing the power extraction value, the original left boundary speed limit is increased so that the stability margin of the compression component remains unchanged, and the right-shifted left boundary speed limit value at the altitude is determined;

[0011] Step S33: Calculate the right-shift left boundary airspeed value at all typical altitudes according to the above steps, thereby determining the left boundary of the flight envelope and forming a stable theoretical working boundary.

[0012] Preferably, in step S33, forming a stable working boundary further includes determining the middle boundary and the right boundary of the working boundary as the original flight envelope boundary when there is no power extraction.

[0013] Preferably, after step S3, the method further includes:

[0014] Step S4: Conduct a high-altitude inlet comprehensive distortion test to obtain the critical distortion index for instability at the left boundary of the envelope at different altitudes, both under no power extraction and maximum power extraction conditions. Maintaining the altitude constant, move the indicated airspeed to the right and conduct an inlet distortion test at a specified maximum power extraction until the critical distortion index is greater than or equal to the allowable comprehensive distortion index at the engine inlet, thereby determining the left boundary of the envelope at that altitude. Connect the indicated airspeeds at the left boundary of the tests at each altitude sequentially to form the left boundary of the new flight envelope that accounts for aircraft power extraction. The remaining envelope boundaries remain consistent with the envelope boundaries without considering aircraft power extraction.

[0015] Preferably, the compression component comprises a fan.

[0016] This application obtains the indicated speed of the engine and other critical distortion indices through pressure distortion tests at different altitudes and different indicated speed conditions, thereby determining the flight envelope of the engine under the influence of actual power extraction, greatly improving the engine aerodynamic stability assessment method, thereby providing power extraction limits within the envelope range, avoiding problems such as engine surge, and has strong engineering application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Flowchart of the method for determining the flight envelope of a turbofan engine for this application. DETAILED DESCRIPTION

[0018] In order to make the purpose, technical solutions and advantages of the implementation of this application clearer, the technical solutions in the implementation of this application will be described in more detail below in conjunction with the drawings in the implementation of this application. In the drawings, the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions. The described implementation is a part of the implementation of this application, not all of the implementations. The implementation described below with reference to the drawings is exemplary and is intended to be used to explain this application, and should not be understood as a limitation on this application. Based on the implementation in this application, all other implementations obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. The implementation of this application is described in detail below in conjunction with the drawings.

[0019] This application provides a method for determining the flight envelope of a turbofan engine. Figure 1 As shown, it mainly includes:

[0020] Step S1, obtaining the load spectrum of aircraft accessory power extraction within the full envelope and the comprehensive distortion index allowed for engine import;

[0021] Step S2, determining the converted speed of the compression component of the turbofan engine when the engine stability margin is weakest;

[0022] Step S3: Perform aerodynamic stability calculation of the compression component at typical altitude and speed points within the flight envelope, taking into account different aircraft power extraction conditions, to obtain the envelope altitude and speed at the converted speed state when the stability margin is weakest, thereby determining the theoretical calculation boundary of stable operation of the engine after power extraction.

[0023] In order to determine the engine flight envelope under the condition of aircraft power extraction and avoid problems such as engine surge that endanger flight, the present invention systematically considers the influence of aircraft power extraction on aerodynamic stability within the entire envelope. First, flight-engine coordination is carried out to obtain the load spectrum distribution of aircraft accessory power extraction within the envelope and the allowable comprehensive distortion index of the engine inlet. Then, the typical state of the engine and the typical point within the flight envelope are selected for theoretical calculation, and the concept of converted power is introduced to obtain the results of the influence of theoretical power extraction on the aerodynamic stability of the engine. By carrying out the high-altitude platform inlet pressure distortion test, the critical distortion when there is no power extraction and when the maximum power extraction is specified is carried out at the left boundary point of the envelope at different altitudes. Index; keep the altitude unchanged, move the indicated airspeed to the right to carry out the specified maximum power extraction intake distortion test, until the critical distortion index is greater than or equal to the allowable comprehensive distortion index of the engine inlet, so as to determine the left boundary of the envelope under the altitude condition; take this altitude as an example, select the left boundary of the envelope under 5 typical altitude conditions for distortion test, and superimpose the indicated airspeed with the upper boundary shifted to the right at each altitude in turn, and finally determine the stable operating boundary of the engine with specified maximum power extraction, so as to obtain the engine flight use envelope under the condition of considering the aircraft power extraction, and establish a method for determining the envelope considering the power extraction; at the same time, the power extraction limit under the condition of specified inlet comprehensive distortion index under different altitudes and indicated airspeeds can also be obtained.

[0024] First, flight and engine coordination is conducted to obtain the load spectrum of aircraft accessory power extraction within the full envelope, including typical common power extraction values ​​(such as aircraft maneuvering control surface adjustment, radar operation, etc.) and maximum power extraction values ​​(all aircraft accessories are simultaneously turned on). The allowable comprehensive distortion index range of the engine inlet is also coordinated.

[0025] Afterwards, for the test of turbofan engine fan and other compression components, the speed at which the engine stability margin is weakest is determined and used as the speed state for subsequent tests;

[0026] Subsequently, theoretical calculation and evaluation of the engine aerodynamic stability under power extraction conditions were carried out. Within the full envelope, the aircraft power extraction value (with multiple power devices turned on) should vary according to the flight status. However, when the aircraft extracts at a constant physical power, its power conversion coefficient will change according to the different flight envelope states.

[0027] The converted power is the product of the extracted physical power and the power conversion factor:

[0028]

[0029] The power conversion factor is a function of the engine inlet total pressure P and total temperature T. The closer to the upper left corner of the envelope, the larger the power conversion factor. Calculations show that as the converted power increases, the fan margin loss increases, and the relationship is essentially linear.

[0030] Since at the same altitude of the envelope, as the physical power extraction increases, the original engine's safe operating speed limit will inevitably shift to the right, so the original no-power extraction envelope limit can be used for the middle and right limits of the original flight envelope; the research is mainly conducted on the left limit of the envelope; according to the method of evaluating the residual margin at the typical state point of the envelope, the fan margin corresponding to different power extractions (no power extraction-specified maximum power extraction) is calculated at each altitude of the envelope. During the calculation process, the engine state is selected as the speed corresponding to the weakest margin in the test results of the fan and other compression components; at the same altitude, according to the fan margin, the right-shifted speed of the working point is calculated, and the right-shifted speed of the upper limit of each altitude is superimposed to finally determine the stable operating limit of the power extraction engine. Thus, the theoretical flight operating envelope of the engine under the condition of considering the aircraft power extraction is obtained;

[0031] In an optional embodiment, this step mainly includes:

[0032] Step S31, calculating the fan margin corresponding to the left boundary speed gauge at a certain altitude (for example, a speed gauge of 300 corresponds to a fan margin of 0.5%);

[0033] Step S32: After the extraction power is increased, the fan margin is reduced. To ensure that the fan margin remains the same as in step S31, the speedometer needs to be increased, that is, the speedometer is moved right until the fan margin remains the same.

[0034] Step S33: Calculate the rightward speed values ​​at all altitudes to form a stable working boundary.

[0035] Finally, a high-altitude intake comprehensive distortion test is carried out. The test process is shown in Table 1. The critical distortion index of instability under no power extraction and maximum power extraction states is obtained at the left boundary point of the envelope at different altitudes. Keeping the altitude unchanged, the indicated speed is moved to the right to carry out the intake distortion test with the specified maximum power extraction until the critical distortion index is greater than or equal to the comprehensive distortion index allowed at the engine inlet, thereby determining the left boundary of the envelope under the altitude condition. Taking this altitude as an example, the left boundary of the envelope under 5 typical altitude conditions is selected for distortion tests in turn, and the indicated speed with the upper boundary shifted to the right at each altitude is superimposed in turn to finally determine the stable operating boundary of the engine with the specified maximum power extraction (V b1n -V b5n ), thereby obtaining the engine flight envelope under the conditions of aircraft power extraction; at the same time, the power extraction limit at different altitudes and indicated speeds under the conditions of specified inlet comprehensive distortion index can also be obtained.

[0036] Table 1 High altitude intake pressure distortion test point plan

[0037]

[0038] This application proposes a method for determining the operating envelope of a turbofan engine, taking power extraction into account within the full flight envelope. By conducting pressure distortion tests at different altitudes and indicated airspeeds during high-altitude inlet airflow, the indicated airspeed at the critical distortion index of the engine is obtained, thereby determining the flight envelope of the engine under the influence of actual power extraction. This significantly improves the engine's aerodynamic stability assessment method, thereby providing power extraction limits within the envelope and avoiding problems such as engine surge. This method has strong prospects for engineering application. This application is the first to propose a method for conducting comprehensive inlet pressure distortion tests under high-altitude conditions, and has been successfully applied to a series of engineering models.

[0039] Although the present application has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications or improvements may be made based on the present application. Therefore, such modifications or improvements, which do not depart from the spirit of the present application, are within the scope of protection claimed in the present application.

Claims

1. A method for determining the flight envelope of a turbofan engine taking into account aircraft power extraction, characterized in that: include: Step S1, obtaining the load spectrum of aircraft accessory power extraction within the full envelope and the comprehensive distortion index allowed for engine import; Step S2, determining the converted speed of the compression component of the turbofan engine when the engine stability margin is weakest; Step S3: performing aerodynamic stability calculations on the compression components at typical altitude and speed points within the flight envelope, taking into account different aircraft power extraction conditions, to obtain the envelope altitude and speed at the converted speed state when the stability margin is weakest, thereby determining the theoretical calculation boundary for stable operation of the engine after power extraction; Step S4: Conduct a high-altitude intake comprehensive distortion test to obtain the critical distortion index of instability under no power extraction and maximum power extraction conditions at the left boundary points of the envelope at different altitudes. Maintaining the altitude constant, move the indicated airspeed to the right and conduct an intake distortion test with a specified maximum power extraction until the critical distortion index is greater than or equal to the allowable comprehensive distortion index at the engine inlet, thereby determining the left boundary of the envelope under the altitude condition. Connect the indicated airspeeds at the left boundaries verified by the tests at each altitude in sequence to form the left boundary of the new flight envelope after considering the aircraft power extraction. The remaining envelope boundaries remain consistent with the envelope boundaries without considering the aircraft power extraction. Wherein, step S3 further includes: Step S31, calculating the stability margin of the compression component corresponding to the indicated airspeed at the left boundary of a certain altitude within the flight envelope; Step S32: After increasing the power extraction value, the original left boundary speed limit is increased so that the stability margin of the compression component remains unchanged, and the right-shifted left boundary speed limit value at the altitude is determined; Step S33: Calculate the right-shift left boundary indicated airspeed values ​​at all typical altitudes according to the above steps, thereby determining the left boundary of the flight envelope and forming a stable theoretical operating boundary; In step S33, forming a stable working boundary further includes determining the middle boundary and the right boundary of the working boundary as the original flight envelope boundary when there is no power extraction.

2. The method for determining the flight envelope of a turbofan engine according to claim 1, wherein: In step S33, forming a stable working boundary further includes determining the middle boundary and the right boundary of the working boundary as the original flight envelope boundary when there is no power extraction.

3. The method for determining the flight envelope of a turbofan engine according to claim 1, wherein: The compression component includes a fan.

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