A method for fan pressure ratio correction of a turbofan engine

Abstract

This invention discloses a fan pressure ratio correction method for turbofan engines, relating to the field of aero-engine design. Within a fan pressure ratio correction threshold range, different fan pressure ratio correction coefficients are selected from low to high. FPC To adjust the plane 13 Measured average total pressure P T13 The corresponding theoretical net installation thrust is calculated. FNIN1 calc and theoretical total flow W1 cale To find the pressure ratio of each fan FPR Reduce residual error RERR smallest FPC min This invention corrects the fan pressure ratio by multiplying the scalar form of the fan pressure coefficient (FPC) by the measured fan pressure ratio (FPR), resulting in the corrected fan pressure ratio. This minimizes the error between the calculated value and the value obtained from the ground test bench.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of aero-engine design. More particularly, the present application relates to a method for correcting fan pressure ratio of a turbofan engine. BACKGROUND

[0002] Thrust Flight Test Demonstration (IFTD) is a very complex process, as there are many difficulties due to the inability to directly measure the thrust in flight. Therefore, a series of indirect measurements are required, and then the engine thrust is obtained by analyzing and calculating according to these information. In order to ensure the correctness of the calculation, all measurements must be strictly implemented in accordance with the predetermined method. In the existing method, the gas path analysis method is particularly prominent, but this method only considers the characteristics of the gas flowing through the engine.

[0003] Fan pressure ratio refers to the ratio of total pressure at the fan outlet to that at the inlet, which is an important parameter to measure the degree of air compression by the fan, reflecting the ability of the fan to do work on air per unit time. The inclination, curvature, number of blades, and blade tip clearance will affect the fan pressure ratio. The greater the blade inclination, the greater the pressure difference between the upper and lower surfaces of the blade, and the greater the wind pressure at the same speed, but too large may cause backflow phenomenon and reduce performance; the greater the blade curvature within a certain range, the greater the gas kinetic energy, and the greater the wind pressure. The higher the speed, the stronger the fan's ability to compress air, and the pressure ratio will also increase accordingly. The larger the air density, the higher the pressure ratio generated by the fan under the same conditions. The larger the fan diameter, the stronger its ability to compress air, and the pressure ratio will also increase accordingly. The installation position of the fan and the surrounding obstacles will affect its air intake and exhaust efficiency, and thus affect the pressure ratio.

[0004] Fan pressure ratio directly affects the thrust and fuel efficiency of the turbofan engine. Higher pressure ratio can increase the engine thrust, but it will also increase fuel consumption. Fan pressure ratio determines the flow state of air in the fan, including flow velocity, pressure distribution, etc., which in turn affects the aerodynamic performance of the entire engine. Different flight conditions and mission requirements have different requirements for fan pressure ratio. For example, in high altitude areas or high speed flight, higher pressure ratio is needed to ensure the performance of the engine.

[0005] Fan pressure ratio is one of the key parameters to measure the performance of the turbofan engine. By reasonably designing and adjusting the fan pressure ratio, the thrust, fuel efficiency and adaptability of the engine can be optimized to meet the needs of different flight missions. At the same time, fan pressure ratio is also an important basis for engine design and optimization, which has important significance for improving the overall performance and reliability of the engine. SUMMARY

[0006] It is an object of the present application to solve at least the above problems and / or disadvantages and to provide at least the advantages described later.

[0007] To achieve these objectives and other advantages of the present invention, a method for correcting the fan pressure ratio of a turbofan engine is provided, comprising:

[0008] Within the fan pressure ratio correction threshold range, different fan pressure ratio correction coefficients are selected from low to high. FPC To adjust the plane 13 Measured average total pressure P T13 The corresponding theoretical net installation thrust is calculated. FNIN1 calc and theoretical total flow W1 cale To find out the pressure ratio of each fan FPR Reduce residual error RERR smallest FPC min This completes the correction of the fan pressure ratio;

[0009] Wherein, the plane 13 It refers to the plane behind the fan.

[0010] Preferably, it includes:

[0011] S1. Obtain the measured net installation thrust through ground testing. FNIN 1 meas Actual total flow W 1 meas , P T13 ;

[0012] S2, Settings FPC The initial value is obtained, and the plane is calculated using the following formula. 13 The average total pressure required to minimize residual error P* T13 :

[0013] P* T13 = FPC × P T13

[0014] S3, based on P* T13 The engine parameters obtained from ground tests and the nozzle coefficients from model tests are used to calculate the thrust, in order to obtain the theoretical net thrust for installation. FNIN 1 calc Theoretical total flow W 1 calc ;

[0015] S4, Calculate the plane based on the following formula 13 residual errorRERR :

[0016]

[0017] In the above formula, Δ FNIN 1 is FNIN 1 calc the installation net thrust difference of FNIN 1 meas , ΔW 1 is W 1 calc the total flow difference of W 1 meas ;

[0018] S5, the residual error minimum value of RERR 1 RERR min is judged, if RERR < RERR min , the stepwise iterative judgment is performed on FPC 1 , otherwise, FPC 1 is assigned to FPC 1 min , RERR 1 is assigned to RERR 1 min , and the stepwise iterative judgment is performed on FPC 1 again;

[0019] S6, if the iteration does not exceed the threshold value, the stepwise adjustment is performed on FPC 1 , and returns to S1, otherwise, the fan pressure ratio correction is completed.

[0020] Preferably, in S3, the FNIN 1 calc is obtained by the following formula:

[0021]

[0022] In the above formula, F N,calc is the standard net thrust given by the engine design party, is the internal scouring resistance of the engine.

[0023] Preferably, in S3, the W 1 calc is obtained by the following formula:

[0024]

[0025] In the above formula, W 0,ref is the reference flow obtained by the calibrated ground bench test, t2,calc P is the total pressure at the inlet of the air duct obtained by the model test, and Tt2,calc Tt is the total temperature at the inlet of the nozzle obtained from the model test, P t2,ref P is the total pressure at the inlet of the nozzle obtained from the ground test bench, T t2,ref Tt is the total temperature at the inlet of the nozzle obtained from the ground test bench.

[0026] The present application at least includes the following advantages: the error function designed in the method considers the deviation in the thrust and flow calculation, the error function aims to minimize the error by using the information obtained from the engine test bench and applying a correction factor, i.e. fan pressure correction coefficient (FPC), different from the prior art which only relies on a single coefficient linear correction, the present application searches in the interval of 0.90-1.10 with a step of 0.001, minimizes the composite residual error containing both thrust error and flow error, and thus reduces the uncertainty of fan pressure ratio correction to within 0.3% for the first time.

[0027] Further, in order to minimize the error between the calculated value and the value obtained from the ground test bench, the present application adopts the fan pressure coefficient (FPC) in the form of a scalar to multiply the measured fan pressure ratio (FPR), i.e. the corrected fan pressure ratio.

[0028] Other advantages, objects and features of the present application will be apparent to those skilled in the art from the following description, and will be appreciated when the application is read in conjunction with the drawings. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 The flow chart of the application of the fan pressure ratio correction method of the present application;

[0030] Figure 2 The flow chart of the thrust calculation using the pressure ratio correction of the present application;

[0031] Figure 3 The flow chart of the calculation of FPC of the present application;

[0032] Figure 4 The structural diagram of the low-pressure turbofan engine with a booster stage divided by sections in the prior art;

[0033] Figure 5 The comparison chart of the results of the method of the present application and the relative power plant performance model calculation under the condition of flight altitude of 42000ft and flight speed of 0.85Ma. DETAILED DESCRIPTION

[0034] The present application will be further described in detail below with reference to the drawings, so that those skilled in the art can implement the present application according to the description and the drawings.

[0035] A fan pressure ratio correction method of a turbofan engine, the general idea as shown in Figure 1 , comprising:

[0036] Step one, the data input provided by two test methods.

[0037] Ground test: on the one hand, it provides engine parameters for thrust calculation. It should be noted that in the thrust calculation model of the turbofan engine (whether on the ground test bench or in flight), the "engine parameters" that must be actually input can be summarized into 6 categories and about 20 items. The following commonly used symbols and physical meanings are given according to the categories:

[0038] 1. Parameters related to fan / compressor performance: N1, N2 (or N1K, N2K) representing physical or converted speed; FPR representing fan pressure ratio, which is P*T13 / Pt2 after correction by the present application; OPR representing total pressure ratio; BPR representing bypass ratio; η_fan, η_LPC, η_HPC representing isentropic efficiency.

[0039] 2. Parameters related to combustion and turbine: T3, T4, T45, T5 representing total temperature at each cross section; WF or QF representing fuel flow or corrected fuel flow; η_burn representing combustion efficiency; π_burn representing combustion chamber total pressure recovery coefficient.

[0040] 3. Parameters related to nozzle / tailpipe: A8, A9 (or Ag) representing throat / outlet geometric area; CF_core, CF_fan, CFG_core, CFG_fan representing flow coefficient and thrust coefficient given by model test; NPR_core, NPR_fan representing nozzle pressure ratio.

[0041] 4. Parameters related to inlet and nacelle: Pt2, Tt representing incoming total pressure and total temperature; M0 (or Ma) representing flight Mach number; Re_throat representing throat Reynolds number (Re>2×10 6 in model test); FRAM, FSCR representing ram drag and scouring drag given by CFD or wind tunnel.

[0042] 5. Parameters related to environment / flight conditions: H representing altitude; p0 representing total pressure; T0 representing total temperature; ρ0 representing air density; g0 representing local gravitational acceleration (g0 needs to be corrected only in hypersonic missions).

[0043] 6. Parameters related to auxiliary calibration factors: FPC representing fan pressure ratio correction coefficient (optimized within the range of 0.90-1.10); RERRmin representing residual convergence threshold (0.005-0.010 in engineering).

[0044] Another aspect provides a measured net installed thrust obtained by testing the ground test device FNIN1 meas , measured total flow W1 meas .

[0045] Model test: provide the nozzle coefficient for thrust calculation, the nozzle coefficient mainly involves the nozzle / tail nozzle, such as the throat / outlet geometric area characterized by A8, A9 (or Ag), while the flow coefficient and thrust coefficient given by the model test are characterized by CF_core, CF_fan, CFG_core, CFG_fan, and the nozzle pressure ratio is characterized by NPR_core, NPR_fan.

[0046] Step two, obtain the fan pressure correction coefficient FPC

[0047] In this step, a high-bypass-ratio split-fan turbofan engine is taken as an example Figure 4 The cross-sectional number corresponding to the structural characteristics of the high-bypass-ratio split-fan turbofan engine is given in this step, wherein WaⅠ is the inner channel flow, and WaⅡ is the outer channel flow. It should be noted that the engine in which the inner and outer channel flows are separated and discharged into the atmosphere is called a split-fan turbofan engine. The thrust of such an engine is generated by the inner and outer channels. The ratio of the air flow through the outer channel and the inner channel is called the bypass ratio or flow ratio. The bypass ratio is an important cycle parameter affecting the performance of the turbofan engine), and the fan pressure correction coefficient FPC is obtained as follows: in the threshold interval, different FPC are selected from low to high to adjust the plane 13 of the measured average total pressure P T13 to calculate the theoretical net installed thrust FNIN1 calc and the theoretical total flow W1 cale , find the FPR ( fan pressure ratio , abbreviated as FPR ) that minimizes the residual error residual error ( RERR , abbreviated as FPC min , and the correction curve is obtained FPC , and the specific processing flow is shown in Figure 2 - Figure 3 , including:

[0048] S1, calculate the theoretical net installed thrust FNIN1 calc and the theoretical total flow W1 based on the data (i.e. engine parameters, nozzle coefficients) provided by the two test methodscale ;

[0049] Specifically, calculate the theoretical net installed thrust. FNIN1 calc and theoretical total flow W1 cale The overall process mainly includes:

[0050] S10. The measured net installed thrust of the power unit (i.e., the engine) is directly measured in a ground bench test. FNIN1 meas Actual total flow W1 meas ;

[0051] S11. Collect engine performance data (i.e., tail nozzle coefficient).

[0052] S12. Based on the data from ground tests and model experiments, the theoretical net installation thrust is calculated using equation (1). FNIN1 calc Calculation:

[0053]

[0054] F N,calc This refers to the standard net thrust provided by the engine designer in the traditional sense. For more detailed calculation and derivation formulas regarding internal scouring resistance, please refer to relevant literature.

[0055] The theoretical total flow rate is calculated using equation (2). W1 cale Calculation:

[0056] (2)

[0057] In the above formula, W 0,ref The reference flow rate was obtained from the calibrated ground test bench. Acquisition conditions: standard atmosphere ( P 0 = 101325 Pa, T 0=288.15K), corresponding to a certain reference power state of the engine (such as maximum takeoff or cruise); P t2,calc T represents the total pressure at the intake outlet obtained from the model test; t2,calc P represents the total temperature at the intake outlet obtained from the model test. t2,ref T represents the total intake outlet pressure under the corresponding conditions obtained from the ground test bench; t2,ref The total temperature at the intake outlet of the corresponding state obtained from the ground test bench.

[0058] S2, select the lowest value in the threshold interval of fan pressure correction coefficient FPC as the initial value of FPC, in the case of known FPC, calculate the plane 13 the average total pressure required under the minimum residual error P* T13 :

[0059] P* T13 FPC P T13

[0060] Calculate the residual error of the plane 13 RERR :

[0061]

[0062] In the above formula, Δ FNIN 1 is the installation net thrust difference of FNIN 1 calc and FNIN 1 meas ; ΔW 1 is the total flow difference of W 1 calc and W 1 meas ;

[0063] S5, judge the residual error of RERR and the predetermined minimum value RERR min If RERR < RERR min , stepwise iteration is performed on FPC , otherwise, assign FPC to the predetermined minimum value of fan pressure correction coefficient FPC min Assign RERR to RERR min , and then stepwise iteration is performed on FPC ;

[0064] S6, if the iteration does not exceed the threshold, stepwise adjustment is performed on FPC , and return to S1, otherwise, the fan pressure ratio correction is completed.

[0065] Embodiment:

[0066] ​​​In the flight test for determining thrust during flight, the test power unit is set to a specific converted speed (N1K) (corrected fan speed). By adjusting the thrust of the non-test engine and the flight configuration, the test engine is kept at a specified test altitude and Mach number for stable straight-line flight. After the test engine is stable, the test engine performance data is collected.

[0067] Specifically, during flight tests, the outer bypass nozzle became blocked, and the flow outside the nozzle exhibited a distinct Mach disk structure, while the inner bypass nozzle remained unblocked. Therefore, the flow rates of the inner and outer bypass nozzles needed to be calculated using different flow functions. Figure 3 The thrust calculation process for an outer bypass duct using pressure ratio correction (in) Figure 3 In the middle, P T13 Representing a plane 13 The measured average total pressure (Ma represents the Mach number of the flight speed, T represents the flight temperature, and v represents the flight speed) is used to calculate the thrust of the inner bypass duct, which is similar to that of the outer bypass duct.

[0068] This embodiment selects four representative flight test points (the four flight test points are: the converted engine speeds at 89%, 92%, 95%, and 98%, respectively) to calculate the thrust during flight. The flight altitude at each test point is set to 42,000 ft, the flight speed to 0.85 Mach, and the converted engine speeds to be 89%, 92%, 95%, and 98%, respectively. The thrust calculation results after pressure ratio correction according to this invention (e.g., ...) are used. Figure 5 (As shown in the black box in the middle), further compared with the calculation results of the relative power unit performance model (such as... Figure 5 Compare the two (shown by the red circle in the middle) using... Figure 5 The comparison results show that the deviation between the thrust calculation value after pressure ratio correction using the present invention and the calculation value of the relative power plant performance model does not exceed 2.3%, that is, the calculation results of the present invention can meet the engineering requirements.

[0069] The above solution is merely an illustration of a preferred example and is not limited thereto. When implementing this invention, appropriate substitutions and / or modifications can be made according to the user's needs.

[0070] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention. Other modifications can be readily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A method of fan pressure ratio correction for a turbofan engine, characterized in that, In the fan pressure ratio correction threshold interval, by selecting different fan pressure ratio correction coefficients from low to high FPC to adjust the measured average total pressure of the plane 13 P T13 , the corresponding theoretical net installation thrust FNIN1 calc and the theoretical total flow W1 cale are calculated to find the minimum residual error RERR FPC min at each fan pressure ratio FPR , complete the correction of the fan pressure ratio;​​ The plane 13 is a plane where the rear side of the fan is located. characterized in that it comprises S1, obtain measured net installation thrust by ground test FNIN 1 meas , measured total flow W 1 meas , P T13 ; S2, set FPC the initial value, and the average total pressure required under the minimized residual error is calculated by the following equation 13 P* T13 :​ P* T13 = FPC × P T13 S3、based on P* T13 , engine parameters obtained from ground tests, nozzle coefficients during model tests to calculate thrust to obtain theoretical installed net thrust FNIN 1 calc , theoretical total flow W 1 calc ; S4, calculating the residual error of the plane based on the following formula 13 RERR :​ In the above formula, Δ FNIN 1 is FNIN 1 calc the difference in the net thrust of the installation, FNIN 1 meas the difference in the total flow of the installation, ΔW 1 is W 1 calc the difference in the total flow of the installation, W 1 meas the difference in the total flow of the installation, S5, will RERR The minimum residual error between the target and the target value RERR min Make a judgment, if RERR < RERR min Then for FPC Perform iterative checks step by step; otherwise, FPC Assign to FPC min ,Will RERR Assign to RERR min And then FPC Perform iterative judgment in steps; S6, if the iteration has not exceeded the threshold, then the step adjustment is made to FPC S1, otherwise the fan pressure ratio correction is complete. In S3, the FNIN 1 calc By the following formula: In the above formula, F N,calc Standard net thrust given to engine design team, Engine internal washdown drag.

2. The method of fan pressure ratio correction of a turbofan engine as in claim 1, wherein, In S3, the W 1 calc By the following formula: In the above formula, W 0,ref P is the reference flow obtained from the calibrated ground bench test t2,calc T is the total pressure at the inlet duct exit obtained from the model test t2,calc P is the total temperature at the inlet duct exit obtained from the model test t2,ref T is the total pressure at the inlet duct exit obtained from the ground bench for the corresponding condition t2,ref P is the total temperature at the inlet duct exit obtained from the ground bench for the corresponding condition.

Images