This study conducted atmospheric-pressure laboratory component-level experiments to investigate the performance of the low swirl combustion with liquid kerosene under high bulk flow velocities (above 45m/s) and high inlet temperatures (above 650K) for gas-turbine applications. Effects of the inlet temperature, the temperature rise, the bulk flow velocity and the blockage ratio of the perforated plate on combustion performance are focused. Based on experimental results, the flame stability limits were reported to narrow under the high velocity inlet, the prevaporization and premixing of liquid fuel are key factors that can be facilitated by increasing the inlet temperature and the bulk flow velocity. With the premise of appropriate evaporation and mixing, an increase in the temperature rise would not impair the outlet temperature distribution or pollutant emissions. Indeed, it made the combustion approach the designed ideal states, and reached more uniform distributions of dynamic pressure and temperature and lower emissions of CO and NOx. The potential of liquid-fueled low swirl combustion for gas-turbine conditions was proved by an ultra-low dry basis NOx emission of 4.5ppm at the inlet temperature of 750K and the temperature rise of 400K. Additionally, recommended ranges of four key designed parameters for the combustion are proposed, such as the swirl number above 0.45, the inlet temperature above 750K, and so on.

To enhance aero-engine combustion efficiency, this study investigates the atomization characteristics of selfoscillating sweeping nozzles (SOSN) in crossflow using a Fluent-Basilisk hybrid numerical framework. The synergistic effects of divergence angles (alpha= 30 degrees/60 degrees), fuel pressure drop (Delta P = 0.2/1.5/3 MPa), and crossflow velocity (V = 120 /150 m/s) on spray dynamics are systematically examined. Findings indicate that the 30 degrees nozzle increases jet penetration by approximately 5% over the 60 degrees case. Raising Delta P to 3 MPa expands the spray angle by 64% and increases near-field Sauter Mean Diameter (SMD) by 41%, while a 25% increase in crossflow velocity reduces penetration by 7%. Spatio-temporal analysis further reveals periodic SMD fluctuations with mirrored symmetry. Notably, the SOSN achieves a 43% improvement in spanwise dispersion compared to traditional plain-orifice nozzles. These quantitative insights clarify the spray modulation mechanisms of sweeping jets, providing a robust physical basis for optimizing fuel injection in high-speed propulsion systems.

To achieve the three-dimensional reconstruction of smoke, this paper combines data calculation and processing by taking photos from multiple angles and utilizing computed tomography imaging technology. The SART algorithm and TV regularization are selected as reconstruction algorithms. Since the semi-convergence phenomenon exists in the separate SART algorithm and the lowest point of error in the calculation process is predictable, which can be used as the entry point for the coupling of the SART algorithm and TV regularization, this paper proposes a method of dynamically adjusting the step size of the gradient descent of the TV regularization to ensure that a lower reconstruction error is maintained during the whole process of the calculation, under the condition that the relaxation factor of the SART algorithm is kept unchanged. Comparative evaluation against established methods demonstrates that the proposed approach achieves a statistically significant improvement in accuracy and noise reduction, coupled with enhanced stability and robustness. Especially, the effect is even more pronounced when there is input noise.

A wave rotor and a combustor constitute a closed loop system as the topping cycle of a gas turbine, which is known for performance enhancement. Development of such a new technology shall take continuous optimization based on observable failures, but it has been trapped for decades by a lack of knowledge on how or why the closed loop system may fail. This work proposes a control model for coupled numerical simulation of the closed loop system to calculate the flow field data in failing processes. Results show that the system exhibits a self-regulation ability within certain limits, but excessive adjustment of the exhaust pressure leads to a failure. A transient failing process is demonstrated with the variation of critical fluid dynamic parameters, and critical phenomena of failure was identified as flame out in the combustor and collapse of the unsteady pressure wave system in the wave rotor. It revealed that the adverse interaction loop between the wave rotor and the combustor caused the failure of the closed loop system. This work shall contribute to understanding how a wave rotor-topped gas turbine may fail, so that similar failures can be avoided with optimized control or design in future.

Bayesian methods are employed for model calibration to enhance the accuracy of combustion chamber predictions in the preliminary design phase. This study integrates the DREAM algorithm with performance parameter estimation methods to develop a calibration model for preliminary combustion chamber design. Indicators such as the total pressure recovery coefficient, outlet temperature distribution factor, and combustion efficiency are employed to calibrate the preliminary combustion chamber design. Ultimately, while preserving the total pressure recovery and combustion efficiency performance, the outlet temperature distribution factor is optimized by 62.2 % in underperforming combustion chambers.

Airblast nozzles are widely applied in advanced aeroengine combustors, and their crucial physical phenomena can be simplified to the disturbance and breakup of an annular liquid jet with swirl air. Therefore, the performance of the nozzle is closely related to the primary breakup process, and the linear instability theory provides a theoretical framework for elucidating the primary breakup process. The research focuses on the swirling airflow interacting with the annular liquid jet and derives the dispersion equation for the annular liquid jet based on the linear instability. Through numerical solutions of this dispersion equation, a detailed parametric analysis is conducted. The parametric study shows several key findings. Increasing air density, axial gas velocities (both inner and outer flows), and the rotational Weber numbers promote breakup efficiency. Reducing the liquid jet thickness also enhances breakup efficiency. These changes result in a decrease in primary breakup length and mean droplet diameter. In the process of the decrease in the liquid jet thickness, the dominant force of primary breakup will be changed from the surface tension of the liquid to the aerodynamic force. The swirl air will make the dominant modes of primary breakup change from the axisymmetric modes to the helical modes.

High-frequency oscillations occur in the centrally staged combustor during operation. To effectively suppress them, real-time monitoring of the combustor exit temperature is critical. However, traditional contact temperature measurement methods are inadequate for accurately capturing temperature variations in the turbulent flow field. Tunable Diode Laser Absorption Spectroscopy (TDLAS) with a high acquisition frequency is employed to measure the temperature of the centrally staged combustor, utilizing a non-contact sensing method. The influence of various combustion parameters on the uniformity of combustion within the chamber and the capability of TDLAS to capture temperature data of the combustion chamber under different acquisition frequencies are studied. The results indicate that the staging ratio causes irregular oscillations in the combustion chamber outlet temperature. At an acquisition frequency of 1 kHz, an increase in the staging ratio raises the average temperature at the outlet and slows down the temperature oscillation when other parameters remain constant. At an acquisition frequency of 10 kHz, more small, high-frequency variations in the centrally staged combustor outlet temperature are observed. When the TDLAS system operates at 10 kHz, it can capture more details of the combustion chamber outlet temperature oscillation under the same working conditions and exhibits stronger noise immunity. However, compared with the acquisition frequency of 1 kHz, it cannot sustain long-term measurement.

Modeling complex fluid flow using machine learning is increasingly recognized as a valuable approach for revealing multiphase fluid phenomena. Bubble dynamics represent a classical two-phase flow problem that plays a crucial role in various engineering domains. In this paper, physics-informed neural networks (PINNs) are applied to facilitate incompressible two-phase bubble motion modeling by integrating governing equations and interface evolution equations. The loss function of PINNs consists of multiple loss terms, including initial and boundary conditions constraints, partial differential equations residuals, and volume fraction constraints. The performance of PINNs is influenced by the competing effects of these loss terms. Therefore, we introduce a heuristic adaptive weights approach to automatically adjust loss weights for each training point, avoiding manual tuning and improving the accuracy of PINNs. We investigate typical bubble motion cases, specifically focusing on bubble rising and breakup, to showcase the capabilities of the proposed method. We explore the impact of weights and present the results in comparison to the baselines. Through the bubble breakup case, we illustrate that our model shows superior performance even with more complex scenarios. Then we further discuss the generalization and robustness of our model, showing their indispensability over traditional solvers in gas-liquid two-phase systems. Specifically, we accelerate computation speed in transfer learning without the need to modify the original model. We also show that our method effectively solves ill-posed problems, such as those without initial data or with incomplete or noisy boundary conditions.

This article investigates the atomization characteristics of a streamlined direct-injection atomizer, which finishes the atomization process by coupling the air swirl with the conventional direct injector. First, we used experimental methods to focus on controlling its structural parameters and the liquid-to-gas flow ratio. We used a phase Doppler interferometer to measure the Sauter mean diameter (SMD) of the droplets and used a high-speed camera to capture the atomization field images. The experimental results showed that, under all test conditions, the overall range of the SMD was from 84 to 100 mu m. It was found that a higher liquid-to-gas flow ratio resulted in a smaller SMD, a larger distance between the liquid and air outlets led to a larger SMD, and an increase in the axial angle of the liquid jet led to a smaller SMD. We found the influence parameters of the atomization characteristics of the streamlined direct-injection atomizer based on the dimensional analysis, namely, pi theorem. In addition, a calculation formula for the SMD was proposed, with multiple linear regression conducted on the sample data from experiment. Based on the findings of this study, the streamlined direct-injection atomizer can be used to dynamically control its spray characteristics according to the requirements of aviation engine combustion chambers.

To obtain a comprehensive understanding of the primary breakup mechanism of dual-layer, rotating conical liquid sheets, the spray field of a dual-orifice, pressure-swirl atomizer is observed using highspeed shadowgraphy. The influences of the pressure drop in the primary and pilot flow channels and of the merger of the dual-layer liquid sheet on spray morphology, spray cone angle, and liquid sheet surface fluctuations are investigated on the basis of an analysis of spray field images. Attention is focused on the mechanisms underlying the behavior of the disturbance waves generated during the merger of the dual-layer liquid sheet. The results of this study reveal that the pressure drops in the primary and pilot flow channels affect the spray pattern, spray cone angle, and liquid sheet surface fluctuations. It is found that the influence of the pressure drop in the primary channel is dominant, and the changes in the liquid sheet surface fluctuations are related to the spray pattern. During liquid sheet merger (after the inner sheet has reached the expected spray cone angle), the spray cone angle of the outer sheet decreases, and only after the sheets are in contact with each other does the amplitude of the surface fluctuations become significantly larger and generate more medium- and high-frequency disturbance waves.

Breaking through the limit of conventional compression and combustion, wave rotor and trapped vortex combustors are able to improve the thermal efficiency of gas turbines. Detailed two-dimensional numerical simulations based on Ansys Fluent were performed to study the flow and combustion characteristics of the wave rotor–trapped vortex combustor system. The calculated pressure characteristics agree with the experimental results giving a relative error for average pressure of 0.189% at Port 2 and of 0.672% at Port 4. The flow stratification characteristics and the periodic fluctuations were found to benefit the zonal organized combustion in the trapped vortex combustor. For the six cases of different rotor speeds, as the rotor speed increased, the oxygen mass fraction at the combustor inlet rose and then fell. The proportion of exhaust gas recirculation fell at first and then rose, and the combustion mode became unstable with the dominant frequencies of the fluctuations increasing.

为了全面加深对旋转锥形液膜一次破碎机理的认识,采用高速阴影法对离心喷嘴的喷雾场进行了试验拍摄,并基于喷雾场形态特征详细描述了7种喷雾形态随压降的变化过程,分析了液膜表面波动与液膜穿孔的关系以及导致液膜破碎的机理,重点关注了波动、穿孔和湍流这三种锥形喷雾形态,并对其表面波动特征随压降的变化规律进行了研究.研究表明:液膜的表面波动和液膜穿孔均是由初始速度波动引起的液体聚集从而形成波峰和波谷导致的,在三种锥形喷雾形态中这两种特征一直存在;随着压降增大,在波动锥形喷雾形态中液膜表面波动的波长、振幅和频率均逐渐变大,在穿孔锥形和湍流锥形喷雾形态中液膜表面波动的波长和振幅逐渐减小,频率逐渐增大,且在湍流锥形喷雾形态中,频率组成随压降增大越加混乱.

针对燃烧室初步设计阶段输入参数存在混合不确定性的特点,提出一种概率盒框架下的全局灵敏度分析方法.简单介绍了航空发动机燃烧效率的一维计算方法;在随机和认知混合不确定性的概率盒表征基础上,使用Sobol指标的上下限表征概率盒中随机与认知混合不确定性对响应的贡献程度;最后基于双层嵌套蒙特卡洛/非嵌入式多项式混沌展开(Monte Carlo Simulation/Non-intrusive Polynomial Chaos Expansion,MCS/NIPCE)方法对概率盒灵敏度指标进行求解,筛选出重要变量和次要变量,实现模型的降维.通过某航空发动机燃烧效率的全局灵敏度分析对所提出的方法进行了验证.研究结果表明,Sobol指标的上下限可以显著表征概率盒灵敏度指标,在保证计算精度的前提下,双层MCS/NIPCE方法的计算效率要远远高于传统双层蒙特卡洛(Monte Carlo Simulation,MCS/MCS)方法,可获得考虑随机和认知混合不确定性情况下燃烧效率输入参数的重要性排序.

为了探究极端降雨条件下发动机入口吞雨量,基于欧拉多相流模型,针对不同涵道比发动机,选取不同降雨强度、攻角及飞行阶段进行计算,分析不同条件对于发动机入口吞雨量的影响,并将计算所得结果与国军标中对于吞水的试验条件进行对比.计算结果表明,发动机入口吞雨量会随着降雨强度和飞行速度的增大而增大,但攻角变化对其影响较小.当降雨强度低于709.2mm/h时,发动机入口吞雨量始终低于国军标吞水试验条件中的入口流量最大值5％,能够保证飞行安全.但当降雨强度达到1872mm/h时,爬升阶段的吞雨量高于5％,可能存在安全隐患.

Uncertainties are widely present in the design and simulation of aero-engine combustion systems. Common non-probabilistic convex models are only capable of processing independent or correlated uncertainty variables, while conventional precise probabilistic sensitivity analysis based on ideal conditions also fails due to the presence of uncertainties. Given the above-described problem, an imprecise p-box sensitivity analysis method is proposed in this study in accordance with a multi-dimensional parallelepiped model, comprising independent and correlated variables in a unified framework to effectively address complex hybrid uncertainty problems where the two variables co-exist. The concepts of the correlation angle and correlation coefficient of any two parameters are defined. A multi-dimensional parallelepiped model is built as the uncertainty domain based on the marginal intervals and correlation characteristics of all parameters. The correlated variables in the initial parameter space are converted into independent variables in the affine space by introducing an affine coordinate system. Significant and minor variables are filtered out through imprecise sensitivity analysis using pinching methods based on p-box characterization. The feasibility and accuracy of the method are verified based on the analysis of the numerical example and the outlet temperature distribution factor. As indicated by the results, the coupling between the variables can be significantly characterized using a multi-dimensional parallelepiped model, and a notable difference exists in the sensitivity ranking compared with considering only the independence of the variables, in which input parameters (e.g., inlet and outlet pressure, density, and reference flow rate) are highly sensitive to changes in the outlet temperature distribution factor. Furthermore, the structural parameters of the flame cylinder exert a secondary effect.

为研究自然风下露天试车台航空发动机推力修正的方法,针对典型结构露天试车台开展航空发动机在不同自然风风速(0～5m/s),风向(0～90°)下试车流场的数值仿真研究.研究发现,自然风条件明显影响露天试车发动机进气道周围回流区的分布,以往基于测量二次气流的室内试车台推力修正方法无法用于露天试车台,因此推导出基于发动机内流参数的进气附加阻力计算和测量方法,并结合仿真结果分析不同自然风对露天试车台各阻力修正量的影响.结果表明,对于进气附加阻力,随着风速增大逐渐成正比例增加,最大占总推力1.09％;对于台架迎风阻力,当风向角小于45°时与进气方向风速之间满足近似二次曲线关系,最大占总推力0.18％;无风时由于发动机排气射流对台架周围气流速度的影响,仍有台架迎风阻力.

Primary breakup during atomization is governed by complex mechanisms and is not well understood. Detailed numerical simulations using the volume-of-fluid method augmented with adaptive mesh refinement techniques were performed to study the formation and disintegration of liquid sheets produced from a dual-orifice pressure-swirl atomizer. The calculated atomization characteristics agree with the experimental results given a maximum relative error for the spray cone angle of 4.9% and maximum relative error for the Sauter mean diameter of 7.4%. For the five considered cases, changes in the pressure drop over a certain range do not affect the final spray angle size, but larger pressure drops will cause the liquid sheet to open faster while delaying the merger of the liquid sheets. The perturbation wave that causes the primary breakup of the dual-layer liquid sheets consists of two parts: the initial perturbation wave and the perturbation wave originating from the merger of the dual-layer liquid sheets, which dominates their primary breakup but whose generation is delayed by an increased pressure drop. The axial position when the disturbance wave first grows to its maximum amplitude matches well with the liquid sheet breakup length with a maximum error of 11.9%. Research on the merger of liquid sheets helps to further study the mechanisms of dual-layer liquid sheet primary breakup and guide the understanding of atomization in dual-orifice pressure-swirl atomizers.

Integral three-dimensional printing of aeroengine fuel nozzles is an emerging trend. However, the large relative roughness of the internal flow paths created by this processing method is problematic. To study the influence of the rough surface morphology on atomization performance in geometrically sensitive areas of centrifugal nozzles, this paper describes numerical simulations of the atomization process of five nozzle models with rough orifice sections. The simulation framework considers a coupled internal and external flow in stages. The macroscopic morphology of the numerically calculated spray field is found to be consistent with experimental results, with maximum errors in the Sauter mean diameter, spray angle, and flow rate of just 8.7%, 3.7%, and 6.1%, respectively. The numerical results show that the nozzle's rough surface morphology in geometrically sensitive areas has a non-negligible impact on the liquid film velocity fluctuations, primary breakup, and secondary atomization characteristics. Indeed, the effect on primary breakup is large, with the maximum difference between the five rough-surface models reaching 22.9%. The effect on secondary atomization is small, with a maximum difference of just 5.7% except in the number of droplets, which has a maximum difference of 22.1%. Among the five rough-surface models, the atomization characteristics of the smooth model differ greatly from those of the real model, whereas a power-function model best reflects the real surface morphology. This study provides new ideas for nozzle performance prediction and optimization, and provides a reference for engineering applications of three-dimensional printed centrifugal nozzles.

A wave rotor optimizes the use of energy resources by enhancing thermodynamic cycles, and further optimization of wave rotor geometry is emerging as an attractive research area. Among the geometric features, the stagger angle of channels lacks sufficient study in spite of its important effects. To address this question, this work developed and applied the velocity triangle models to modify the basic geometry of wave rotors for different stagger angles, and investigated the flow fields with two-dimensional numerical methods. Results showed that: (1) different stagger angles worked out similar unsteady pressure wave systems and kept nearly constant compression and expansion ratios of the wave rotor; (2) increased stagger angle made the inlet and outlet flows turn toward the axial direction, which was beneficial to compact and light-weighted integration of the wave rotor to a gas turbine; (3) increased stagger angle made the wave rotor consume more shaft power, but even the maximum shaft power was small. This work revealed a critical mechanism how the velocity variation across an unsteady pressure wave produced rim work in a staggered channel, and made a recommendation to comprehensive optimization of wave rotor geometry for better integration in a gas turbine and acceptable shaft power consumption.