A method for reconstructing boundary conditions of compressor pulsating back pressure considering hydrogen-doped combustion characteristics

Abstract

The application discloses a method for reconstructing pulsating back pressure boundary conditions of a compressor by considering combustion characteristics of a combustion chamber and according to the combustion characteristics, and belongs to the field of aero-engine design.The method comprises the following steps: obtaining pressure pulsation characteristics of the combustion chamber under different hydrogen mixing ratios in a normal pressure environment; establishing an amplitude correction model and a frequency correction model based on a thermoacoustic principle, and mapping the normal pressure data to a high pressure working condition; and constructing an unsteady back pressure boundary function with spatial modal characteristics.The application fully considers the influence of a high temperature and high pressure environment at the outlet of the compressor on the amplitude and frequency of pressure pulsation, and provides a theoretical basis for safe design of a hydrogen mixing / pure hydrogen engine.

Description

Technical Field

[0001] This invention belongs to the field of aero-engine and gas turbine design, and specifically relates to a method for reconstructing compressor pulsating back pressure boundary conditions considering hydrogen-infused combustion characteristics. Background Technology

[0002] Traditional compressor back pressure boundary conditions typically employ steady or simplified harmonic back pressure boundary conditions. However, in hydrogen fuel cell engines, the extremely fast flame propagation speed of hydrogen (laminar flame speed is approximately 8 times that of methane) and extremely high heat release rate lead to intense thermoacoustic coupling pulsations. The amplitude and frequency characteristics of these pulsations differ fundamentally from those of conventional hydrocarbon fuels, and existing back pressure boundary conditions cannot accurately reflect the pulsation characteristics of hydrogen fuel.

[0003] High-pressure full-scale combustion chamber experiments are extremely costly, and most existing ground tests are conducted at atmospheric pressure. Currently, there is no mature theoretical framework to establish a quantitative correlation between atmospheric pressure test data and high-pressure operating conditions, and a lack of a physical mapping mechanism from atmospheric pressure combustion data to the high-pressure compressor boundary. This makes it impossible to accurately construct the high-pressure compressor outlet back pressure boundary conditions during the design phase, making it difficult to apply ground test results to the high-pressure compressor, and consequently, difficult to accurately predict the impact of hydrogen fuel pulsation on the stability of the upstream compressor. Summary of the Invention

[0004] In view of this, the present invention provides a method for reconstructing the compressor pulsating back pressure boundary conditions by considering the hydrogen-infused combustion characteristics of the combustion chamber. The method needs to solve the following key problems: (1) establishing a physical scaling model from atmospheric pressure test data to high pressure operating conditions; (2) reconstructing the compressor back pressure pulsating boundary conditions with spatial modal characteristics. The core is to consider the hydrogen-infused combustion characteristics of the combustion chamber, construct the compressor high-pressure pulsating back pressure boundary using the physical scaling law based on thermoacoustics and combustion dynamics principles, and reconstruct the compressor back pressure pulsating boundary conditions by combining the spatial modal characteristics of the combustion chamber pressure.

[0005] The derivation of the amplitude scaling correction model: The generation mechanism of pressure pulsations in the combustion chamber can be described by the Rayleigh criterion. When the heat release rate fluctuation is in phase with the pressure fluctuation, acoustic energy is continuously injected into the system, and the pulsation amplitude increases. On an acoustic scale, the intrinsic amplitude of the acoustic modes increases linearly with the medium density, and the pressure pulsation amplitude is proportional to the average pressure in the combustion chamber. Therefore... This is a first-order approximation under the linear acoustic assumption.

[0006] The derivation of the frequency scaling correction model is as follows: the dominant frequency of combustion pulsation is determined by the acoustic modes of the combustion chamber, and the frequency of the acoustic modes is proportional to the local speed of sound. Under the same combustion chamber geometry, the temperature difference between high-pressure and normal-pressure operating conditions leads to different sound velocities. This invention assumes that the change in gas composition is proportional to the heat of relativism. The effect is negligible, and this assumption is reasonable for lean premixed combustion that is primarily air-based.

[0007] The present invention is achieved using the following technical solution: The pressure pulsation signal of the combustion chamber under normal pressure is acquired, and the dominant frequency is extracted by frequency domain analysis (FFT or wavelet transform). and pressure pulsation amplitude ; Based on the average pressure at the outlet of the target engine compressor and average temperature Using amplitude correction and frequency correction models that consider the hydrogen reaction characteristics, the pulsation amplitude under high pressure conditions is calculated. and frequency .

[0008] A further technical solution of the present invention is: employing a correction model for amplitude scaling. The modified model used for frequency scaling ; Based on the parameters determined above, a compressor outlet pulsating pressure distribution function with spatial modal characteristics is constructed. .

[0009] A further technical solution of the present invention is: the specific form of the pulsating pressure distribution function is as follows: In the formula, It is a radial distribution function. This is the initial phase; This reconstructed function is used as the outlet back pressure boundary for unsteady compressor calculations.

[0010] Compared with the prior art, the present invention has at least the following beneficial technical effects: The influence of the high temperature and high pressure environment at the compressor outlet on the amplitude and frequency of pressure pulsation is fully considered. The scaling model is based on the Rayleigh criterion and Damköhler number analysis, and the physical mechanism is clear. This invention introduces a radial distribution function It characterizes the spatial non-uniformity of the pressure field at the combustion chamber outlet, making up for the shortcomings of existing methods that mostly assume that the compressor outlet back pressure is uniformly distributed radially, and making the boundary conditions closer to the actual working conditions. The amplitude scaling and frequency scaling formulas are both based on dimensionless analysis and do not depend on specific combustion chamber configurations. Therefore, they are applicable to different hydrogen doping ratios and different types of combustion chambers, and have good versatility and scalability. The reconstructed pulsation boundary can be directly used to evaluate the stability margin of the compressor under hydrogen-blended combustion pulsation, providing a quantitative basis for determining the safe operating envelope of the engine. This method links atmospheric pressure combustion tests, physical scaling laws, and unsteady CFD calculations to form a complete technical chain of "experimentation, scaling, and simulation," filling the methodological gap between ground test data and high-pressure compressor stability assessment. It enables atmospheric pressure test data to effectively support the high-pressure design process, avoiding expensive full-machine full-pressure tests and saving more than 60% of test costs. Attached Figure Description

[0011] Figure 1 The flowchart of this invention illustrates the complete technical route from obtaining atmospheric pressure test data to reconstructing back pressure pulsations.

[0012] Figure 2 : Schematic diagram of pulsating pressure at the compressor outlet boundary, illustrating the outlet pressure pulsation distribution function of an embodiment.

[0013] Figure 3 The compressor aerodynamic characteristic pulsation diagram shows the changes in compressor flow rate, pressure ratio, and efficiency over time.

[0014] Figure 4 The compressor flow rate and pressure ratio characteristic diagram shows the compressor flow rate and pressure ratio characteristic curves under steady back pressure boundary conditions and the compressor flow rate and pressure ratio characteristics under reconstructed pulsating back pressure boundary conditions. Detailed Implementation

[0015] 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.

[0016] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0017] Taking a certain type of aero-engine compressor as an example, some of its design parameters are shown in Table 1 below.

[0018] Table 1 Design parameters of a certain type of aero-engine compressor Design parameters Parameter value Average export pressure, kPa 2900 Average outlet temperature, K 815 Obtain an atmospheric pressure environment ( The combustion chamber pressure pulsation signals are shown in Table 2 below.

[0019] Table 2. Measured pressure pulsation signals in the combustion chamber under normal pressure. Signal name signal value CPU frequency, Hz 240 Pressure pulsation amplitude, kPa 3 Calculated according to the method of this invention, substituting into the scaling formula, we get: , .Pick The compressor pulsating pressure distribution function is: ,like Figure 2As shown. This function is used as the outlet boundary condition for unsteady compressor calculations. Figure 3 and Figure 4 As shown, compared with the calculation using the direct application of combustion chamber pressure pulsation signal, the compressor exhibits obvious pulsation characteristics when calculated using the reconstruction function.

[0020] Table 3 shows the pressure pulsation signals of the combustion chamber under normal pressure environment obtained by changing the hydrogen doping ratio in the combustion chamber.

[0021] Table 3. Measured pressure pulsation signals of the combustion chamber under normal pressure conditions with different hydrogen doping ratios. Signal name signal value CPU frequency, Hz 400 Pressure pulsation amplitude, kPa 5 Calculated according to the method of this invention, substituting into the scaling formula, we get: , .Pick The compressor pulsating pressure distribution function is: This function is used as the outlet boundary condition for unsteady compressor calculations. Compared to calculations using directly applied combustion chamber pressure pulsation signals, the compressor exhibits significant pulsation characteristics when calculated using the reconstructed function. The pulsating back pressure boundary condition reconstruction method provided by this invention remains applicable under different hydrogen doping ratios.

[0022] The above description is a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the scope of the technology disclosed in the present invention, and these modifications or substitutions should all be covered within the scope of protection of the present invention.

Claims

1. A method for reconstructing compressor pulsating back pressure boundary conditions considering hydrogen-doped combustion characteristics, characterized in that, Includes the following steps: Characteristic signal acquisition and preprocessing: Obtain the combustion chamber pressure pulsation signal under normal pressure, and extract the dominant frequency through frequency domain analysis (FFT or wavelet transform). and pressure pulsation amplitude ; Trans-pressure ratio physical parameter scaling, based on the average pressure at the target engine compressor outlet. and average temperature Using amplitude correction and frequency correction models that consider the hydrogen reaction characteristics, the pulsation amplitude under high pressure conditions is calculated. and frequency ; By reconstructing the pulsating backpressure boundary function and combining it with the determined parameters, a compressor outlet pulsating pressure distribution function with spatial modal characteristics is constructed. .

2. The method according to claim 1, characterized in that, The amplitude scaling adopts the following modified model: .

3. The method according to claim 1, characterized in that, The frequency scaling adopts the following modified model: .

4. The method according to claim 1, characterized in that, The specific form of the compressor outlet pulsating pressure distribution function with spatial modal characteristics is as follows: ,in It is a radial distribution function. This is the initial phase.

5. A method for reconstructing compressor pulsating back pressure boundary conditions considering hydrogen-doped combustion characteristics, characterized in that, Includes the method as described in any one of claims 1 to 4.

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