Turbofan Engine Research Articles

Impact of circumferential inlet distortion on different types of stall inceptions in a transonic compressor

The application of higher bypass ratios and lower pressure ratios significantly reduces specific fuel consumption with the development of turbofan engines. However, it also increases the risk of flow separation at the intake, leading to severe circumferential non-uniform inlet conditions. This study aimed to present an experimental investigation on instability evolutions of the compressor under circumferential non-uniform inlet conditions. Two stall inceptions regarding the different spatial scales and initial locations were selected to investigate this issue. The experiments were carried out on one tested rig, which the stall inceptions verified with the rotational speeds. At 65% design rotational speed (Ω), the stall inception was the spike, which was triggered by disturbances within serval pitches scale at the tip. Consequently, the spike-type stall inception was sensitive to circumferential distortion and led to a shrunk stall margin of the compressor. With the rotational speed increasing to 88%Ω, the stall inception switched to partial surge, which was induced by the flow blockage in the hub region around the full-annular. The results indicated that the partial surge was insusceptible to the circumferential distortion, which caused an extended stall margin with a lower stalled mass flow rate. In summary, the influence of distortion on the stability of the target compressor was found to be determined by the stall inception.

The Advection Boundary Law in absence of mean flow: Passivity, nonreciprocity and enhanced noise transmission attenuation

Sound attenuation along a waveguide is intensively studied for applications ranging from heating and air-conditioning ventilation systems, to aircraft turbofan engines. In particular, the new generation of Ultra-High-By-Pass-Ratio turbofan requires higher attenuation at low frequencies, in less space for liner treatment. This demands to go beyond the classical acoustic liner concepts and overcome their limitations. In this paper, we discuss an unconventional boundary operator, called Advection Boundary Law, which can be artificially synthesized by electroactive means, such as Electroacoustic Resonators. This boundary condition entails nonreciprocal propagation, meanwhile enhancing noise transmission attenuation with respect to purely locally-reacting boundaries, along one sense of propagation. Because of its artificial nature though, its acoustical passivity limits are yet to be defined. A thorough numerical study is provided to assess the performances of the Advection Boundary Law, in absence of mean flow. An experimental test-bench validates the numerical outcomes in terms of passivity limits, non-reciprocal propagation and enhanced isolation with respect to local impedance operators. Guidelines are outlined to properly implement the Advection Boundary Law for optimal noise transmission attenuation. Moreover, the tools and criteria provided here can also be employed for the design and characterization of other innovative liners.

A novel method for aero-engine time-series forecasting based on multi-resolution transformer

Time-series forecasting is widely studied in the data-driven component-level modeling, fault diagnosis, and performance prediction of aero-engines. The operational data of aero-engines have the characteristics of complexity and nonlinearity. This paper proposes a multi-resolution transformer (MRT) model for the non-steady state process of aero-engines. This transformer-based model can learn temporal patterns of different scales by performing multi-resolution down-sampling and patch-based tokeniczation on the input time-series. On this basis, a two-stage multi-resolution transformer (TSMRT) framework is proposed for the entire processes time-series modeling of aero-engines. The TSMRT framework employs Augmented Dickey-Fuller (ADF) test to classify aero-engine operational data into steady state processes and non-steady state processes, and models the two processes separately using time–frequency feature neural network (TFNN) model and MRT model. The time-series forecasting performance of the MRT model is validated on three publicly available benchmark datasets and an ablation study is conducted on turbofan engine test bench datasets. The results indicate that the TSMRT framework demonstrates superior forecasting performance across steady state, non-steady state, and entire processes. This framework stands out as a novel method for component-level modeling of aero-engines.

A Practical Example of Applying Machine Learning to a Real Turbofan Engine Issue: NEOP

A Practical Example of Applying Machine Learning to a Real Turbofan Engine Issue: NEOP

Performance and Exergy analysis of TurboJet and TurboFan configurations with Rotating Detonation Combustor

Conventional gas turbine is reaching its saturation level and further improvement in the cycle efficiency is possible through redesigning the cycle. One of the effective methods is to introduce a Pressure Gain Combustor (PGC) in place of the conventional deflagration combustor as PGC contributes to a considerable gain in thermal efficiency. Pulsed Detonation Combustor (PDC) and Rotating Detonation Combustor (RDC) are the two most prevalent combustor designs for pressure gain combustion. The major challenges of integrating PGCs to existing conventional cycles are the highly unsteady exhaust flow from PGC, high exhaust temperatures from PGC, potential back flow from combustor to compressor. As turbines are designed for much steadier flows, this unsteady exhaust flow and high temperature exhaust gas from PGC is challenging for the turbine of the cycle and its design. One of the solutions is to have an ejector between the PGC and turbine in order to reduce the flow fluctuations, flow velocity and flow temperature. In this work, different cycle layouts of Turbojet and Turbofan engines working with RDC are described. Low order RDC and ejector models are used in this paper. As the ejector is being used, the compressed air from the compressor is split for RDC, ejector, turbine blade cooling. The different cases for the compressed air split are also examined. The performance parameters of the engines are evaluated for different compressor pressure ratios, fan pressure ratios, bypass ratios. Finally, an exergy analysis is performed on all components.

Assessing the particulate matter emission reduction characteristics of small turbofan engine fueled with 100 % HEFA sustainable aviation fuel

With the continuous increase in global air transportation, the impact of ultrafine particulate matter (PM) emissions from aviation on human health and environmental pollution is becoming increasingly severe. In addition to carbon reduction throughout the lifecycle, Sustainable Aviation Fuels (SAF) also represent a significant pathway for reducing PM emissions. However, due to issues such as airworthiness safety and adaptability, existing research has mostly focused on the emission performance of SAF when blended with traditional fuels at <50 %, leaving the emission characteristics of higher blending ratios to be explored. In this study, using measurement methods recommended by the International Civil Aviation Organization (ICAO), the PM emission reduction characteristics of small turbofan engines fueled with 100 % Hydroprocessed Esters and Fatty Acids (HEFA)-SAF were experimentally evaluated and compared with traditional fuels RP-3 and Diesel, while avoiding the interference of lubricant blending combustion. The results showed that the peak number concentration of particle size distribution (PSD), PM total number, as well as the number and mass concentration of non-volatile particulate matter (nvPM) decreased initially and then increased with rising thrust conditions. HEFA-SAF exhibits PSD with smaller diameters, and the Geometric Mean Diameter (GMD) ranges from 7.7 nm to 20.3 nm under all conditions. Both volatile particulates (vPM) and nvPM from HEFA-SAF are significantly reduced, with nvPM number emission index (EIn) being 92 % and 71 % lower than Diesel and RP-3, respectively. The nvPM mass emission index (EIm) also shows reductions of 96 % and 89 % compared to Diesel and RP-3. Microscopic characterization also indicated that using HEFA-SAF emitted fewer and smaller PMs. This study establishes a foundation for evaluating the effectiveness of 100 % SAF in reducing PM emissions within the aviation sector, and contributes to the airworthiness regulations development related to the use of SAF in a variety of application environments, alongside enhancing environmental protection measures.

Performance Analysis and Aerodynamic Design of Axial Flow Compressors

The main objective of the paper is to analyze theperformance of axial flow compressors and to generate asystematic design approach which enables to designsubsonic flow ones. In order to investigate the validity of this approach, the LP axial flow compressor of the RR SpeyMK511 turbofan engine is taken as an example. The designcalculations were based on thermodynamics, gas dynamics,fluid mechanics and empirical relations. The flow isassumed to be of two-dimensional compressible type withconstant axial and rotor blade velocities with a free-vortexswirl distribution. Design calculations includethermodynamic properties of the working fluid, number ofcompressor performance parameters such as, stagetemperature rise and number, flow and blade angles (bladetwist), velocity triangles and relative inlet Mach number atrotor blades tips as well as blades tip and hub diameters. Arepeated calculation is made to determine these parametersalong compressor stages. The variation of velocity whirlcomponents, air and blade angles, deflection and degree ofreaction from root to tip of the blades were also determined.The twist of the blades along the blade length is setaccording to the recommended values in order to obtainsmooth blade twist profile.

The Electrostatic Induction Characteristics of SiC/SiC Particles in Aero-Engine Exhaust Gases: A Simulated Experiment and Analysis

This study investigates the electrostatic induction characteristics of silicon carbide-fiber-reinforced silicon carbide (SiC/SiC) particles within aero-engine exhaust gases using a dedicated J20 turbojet engine experimental platform. Our comprehensive experiments explored the electrostatic properties of SiC/SiC particles under varying engine operational states—specifically focusing on different thermal conditions, particle mass concentrations, particle sizes, and exhaust gas velocities compared to those of common engine exhaust constituents like carbon (C) and iron (Fe) particles. The results demonstrate that SiC/SiC particles consistently maintain a stable positive charge across varied temperatures, significantly diverging from the behaviors of carbon (C) and iron (Fe) particles. Additionally, our findings reveal that higher mass concentrations of SiC/SiC particles, smaller particle sizes within a certain range, and greater exhaust gas velocities of the aero-engine all lead to increased particle charge and more pronounced electrostatic induction characteristics. This study highlights the potential of electrostatic sensors for the early detection and diagnosis of failures in aero-engines, offering crucial insights into the development of more resilient real-time aero-engine health monitoring systems.

Research on performance seeking control of turbofan engine in minimum hot spot temperature mode

Abstract The uneven temperature distribution at the combustion chamber outlet seriously affects the working life of the engine. In order to reduce the heat spot temperature at the combustion chamber outlet, a performance optimization control method of the engine minimum heat spot temperature pattern is proposed. Firstly, based on CFD method, the temperature distribution characteristics of combustion chamber outlet under different working conditions were obtained, and a component-level model of turbofan engine was established to characterize the heat spot temperature at combustion chamber outlet. Secondly, the high precision and high real-time engine on-board model is established by deep neural network. Compared with the component-level model, the average relative error of each performance parameter is less than 0.3 %, and the real-time performance is improved by 12 times. Finally, based on the feasible sequential quadratic programming algorithm, the performance optimization control of the minimum hot spot temperature model in the typical flight envelope is simulated and verified. The simulation results show that under the condition of ensuring the safe and stable operation of the engine and constant thrust, the heat spot temperature at the combustion chamber outlet decreases by 21 K maximum. Compared with the conventional minimum turbine front temperature optimization mode, the minimum heat spot temperature mode significantly reduces the heat spot temperature at the combustion chamber outlet.

Stand characteristics of the GTM 400 MOD turbojet engine

Miniaturization of turbine jet engines not only enables testing of fuel mixtures but also opens up new possibilities for their use in smaller aircraft. In this work, measurements were carried out in the GTM 400 MOD engine in order to create the stand characteristics of unit thrust and specific fuel consumption. For both parameters, polynomials were determined describing their changes in the range of rotational speeds used. The work is the first stage of research under the rector's grant. Its goal is to create a hybrid turbojet engine powered by aviation kerosene and hydrogen. The reason for the research is to check the possibility of using hydrogen in turbomachinery engines. Hydrogen is one of the fuel additives approved for use by the European Union, which forces the aviation industry to reduce exhaust emissions into the atmosphere. Hydrogen can not only enrich aviation kerosene but also become an alternative fuel.

Numerical Simulation of Workflow for Evaluating Flame Tube Thermocyclic Durability

ABSTRACT This paper explores strategies for extending the operational lifespan of flame tubes in turbofan engines – a critical component for maintaining engine efficiency and reliability, in line with global trends aimed at maximizing the use of laid reserves of aircraft engine performance. Utilizing a combination of advanced computational simulations and empirical research, the study meticulously analyzes the internal processes within the flame tube of the AL-31F turbofan engine. A detailed geometric model and finite element grid were created and adapted to simulate various operating conditions and assess their impact on the flame tube’s performance. Special attention is given to understanding the thermal and mechanical stresses that influence its durability and serviceability. The results, compared against experimental data, validate the simulations and are crucial for identifying critical sections prone to damage, thereby facilitating enhanced decision-making regarding maintenance schedules and overhaul practices. This approach not only aims to minimize downtime and reduce maintenance costs but also extends the service intervals for critical engine components, thereby improving thermocyclic durability based on the damage mechanisms identified.

A New Saturation Control for Uncertain System Using Diffeomorphism Approach: Application to Turbofan Engine

A New Saturation Control for Uncertain System Using Diffeomorphism Approach: Application to Turbofan Engine

Central cone film cooling scheme of turbofan engine based on multi-fidelity simulation

To improve the computational efficiency of multi-fidelity simulation, an improved fully coupled method was proposed, which was applied to the coupled simulation of a 3-D model of an exhaust system and a 0-D model of a turbofan engine. Different from conventional approach, by “truncating” the engine model, the CFD calculation of the exhaust system can be decoupled from the solution of nonlinear equations in the engine model, and an outer iteration equation set was constructed to solve the multi-fidelity model. It was found that the improved fully coupled method has better computational efficiency than traditional methods while maintaining equivalent computational results. Then, the improved fully coupled method was applied to the design of the central cone film cooling system, the influence of cooling gas bleed mechanism, the hole open area ratio of the central cone and hole density, hole direction, hole shape on the infrared characteristics was investigated. The impact of central cone film cooling on the overall performance of the engine was quantitatively evaluated. Combined with various favorable factors, when maintaining the HP rotor speed unchanged, the integrated infrared radiation intensity of the central cone under supersonic cruise conditions is reduced by 93 % compared to the uncooled state, while the engine thrust increases by 0.3 % and fuel consumption rate increases by 0.18 %. The multi-fidelity simulation method proposed in this paper and the conclusions obtained are of great significance for the structural design of low-infrared exhaust systems.

Enhancing aero-engine thrust response: Accounting for combustion delays

In scenarios like aircraft landing, Rapid Thrust Modulation (RTM) is required to achieve high-precision attitude and trajectory manipulations. However, the traditional manipulated variable in aero-engines, specifically the fuel flow, experiences sluggishness in adjusting thrust (Fn) due to combustion delays. In contrast, geometric variable areas, like the nozzle throat area (A8), offer rapid responsiveness but have limited thrust-adjusting capacity. Hence, the proposal of an innovative parallel Valve Position Control (VPC) scheme, combining redundant control inputs, emerges as a groundbreaking solution to enable RTM. In the pursuit of achieving RTM, the non-minimum phase thrust responses are first addressed, which has not been recognized previously to the best of the author's knowledge. This includes the implementation of a new valve position control (VPC) structure, incorporating a dual input Single Output (DISO) system, which is vital for optimizing response time and minimizing the delayed effects in combustion processes. After proper selection of operating conditions, the synthesis process of VPC is outlined by three key requirements, including: 1) realizing the 10 rad/s thrust bandwidth despite the combustion delay; 2) ensuring continuous modulation capability by mid-ranging the A8; 3) decoupling the A8 and thrust during flights. The VPC controller is implemented and compared with the classical Edmond algorithm in a turbofan engine. Results emphasize VPC's robustness in handling combustion delays, meeting specified requirements, and showcasing its potential as an effective RTM solution. Practically, the VPC system's architecture allows for critical rapid thrust changes within a 10 rad/s bandwidth, essential for operations like VSTOL aircraft maneuvers.

Direct-Noise of an Ultrahigh-Bypass-Ratio Turbofan: Periodic-Sector vs Full-Annulus Large-Eddy Simulations

The tonal and broadband noise of an ultrahigh-bypass-ratio fan stage, which has been developed at École Centrale de Lyon, is studied using large-eddy simulations (LES). Wall-modeled LES of a periodic sector and a 360-deg full fan stage have been performed at approach conditions, which is a relevant operating point for aircraft noise certifications. The fan noise is directly obtained from the fully compressible LES, using a well-refined unstructured mesh, and compared with state-of-the-art analytical models. The impact of the periodic boundary conditions, which are often used for high-fidelity simulations of turbofan engines, is assessed. The results from the 360-deg and periodic-sector LES are compared from aerodynamic and acoustic perspectives, including an analysis of the mean and turbulent flow quantities and sound-pressure spectra. Aerodynamic parameters show similar results for both configurations. However, the fan blade loading is slightly reduced in the 360-deg- LES near the blade tip. Acoustically, lower sound power levels at the intake and exhaust sections of the fan stage are obtained in the 360-deg LES, when compared to the periodic sector LES, particularly at low and middle frequencies. This can be associated with lower coherence levels in the fan wakes and smaller spanwise correlation lengths at the trailing edge of the blades. The modal content of the acoustic field has also been analyzed in detail and shows that the periodic sector LES cannot correctly simulate the modal content of the fan noise.

Low-frequency sound attenuation by coiled-up meta-liner with nonuniform cross sections under grazing flow

We report a kind of coiled-up meta-liners with nonuniform cross sections (CMNC), which can efficiently attenuate low-frequency sound waves under grazing flow with a deep subwavelength thickness (e.g., ∼λ/17 at 500 Hz). At a grazing flow Mach number of 0.26, the average transmission loss of the meta-liner is 12.6 dB at 500–1000 Hz, which is twice as much as that of a double-degree-of-freedom acoustic liner of the same size. Physically, the nonuniform cross-sectional distribution and significant cross-sectional area ratio enhances vortex shedding, thus resulting in severe acoustic energy dissipation. The excellent low-frequency acoustic attenuation performance of CMNC is investigated thoroughly with experimental, theoretical, and numerical methods. This work provides an avenue for low-frequency noise reduction in grazing flow scenarios (e.g., in a high bypass ratio turbofan engine).

Effect of alternative biogas-methane fuels use on performance and emissions in turbojet engine

Effect of alternative biogas-methane fuels use on performance and emissions in turbojet engine

High-Fidelity Simulation and Performance Analysis of Twin-Spool Turbofan Engine Based on Multi-dynamics Approach

High-Fidelity Simulation and Performance Analysis of Twin-Spool Turbofan Engine Based on Multi-dynamics Approach

Quantification and kinetics of nitrogen mass gain during high temperature oxidation of titanium in air

Improving the high-temperature oxidation resistance of titanium alloys in air is a prerequisite for extending their use in turbojet engines. A better understanding of the role of atmospheric nitrogen is required for this purpose. Here, we studied the insertion kinetics of nitrogen in titanium at 650 °C in air up to 100 h. Moreover, the nitrogen mass gain, and its ratio over the total mass gain, were quantified as a function of the oxidation duration by using Nuclear Reaction Analysis. It was found that nitrogen inserts into titanium with a parabolic kinetics and a rate constant about 1500 times smaller than oxygen.

Self-tuning speed and flow control of micro turbojet engines based on an improved evolutionary strategy

At present, the controllable parameters of micro turbojet engines in engineering applications are mainly speed-fuel flow (hereinafter referred to as flow) control, in which closed-loop proportional–integral–derivative (PID) control is mostly used to achieve a stable control of engine speed under slow engine conditions. For the optimal adjustment of PID parameters, this paper designs an improved evolutionary strategy for the self-tuning of control parameters in the engine speed and flow control system and formulates an improved PI controller based on a neural network. The simulation experimental results show that the method can realistically achieve stable and fast control of the engine under above slow conditions.