Military Aero Engines Research Articles

Numerical investigation into the effects of aft deck angle on the flow characteristics of a serpentine nozzle

For modern military aero-engine, the serpentine nozzle with aft deck is deployed to meet the requirements of stealth and integrated design. Different from existing studies which emphasize the rectangular nozzles and corresponding infrared radiation impact, the effect of the aft deck angle on flow characteristics of serpentine nozzles with a focus on the internal flow, the shock system, the jet’s evolution, and the performance parameters are systematically investigated in this paper. This study is carried out through three-dimensional numerical simulations, which are validated by the experiment. The results show that the aft deck with different angles has a significant impact on the overall flow characteristics, such as the static pressure and the three-dimensional shock system, as a result of the asymmetry and the contraction/expansion effects on the jet. Specifically, upward-deflected aft decks lead to a re-compression effect and the variation of the internal static pressure value can be up to 7%, whereas for downward-deflected aft decks, the effect on the internal flow can be neglected in under-expansion conditions. In addition, the aft deck angle and the extent of boundary layer separation greatly affect the thrust performance and the vortex evolution, which determines the downstream evolution of the jet cross-section. Effective thrust coefficient is closely tied to the thrust vector angle, with the coefficient reaching its zenith when the thrust vector angle is closest to 0°. This study reinforces understanding of the interrelated problems and may facilitate the development of the optimal aft deck angle for various applications.

A Fault Diagnosis Analysis of Afterburner Failure of Aeroengine Based on Fault Tree

The afterburner is essential for military aeroengines, providing rapid thrust increase during critical maneuvers. However, complex failure mechanisms pose challenges for fault diagnosis and troubleshooting. This study investigates a specific aviation engine’s afterburner engagement principle and typical faults, using fault tree analysis and computational fluid dynamics (CFD). We propose a hybrid diagnostic fault architecture combining traditional observer fault diagnosis with fault trees for online fault diagnosis of critical faults. Simulations and test bench verification confirm the feasibility and effectiveness of our approach, offering valuable insights and guidance for addressing afterburner engagement issues in aviation engines.

Review on Anti-Fatigue Performance of Gradient Microstructures in Metallic Components by Laser Shock Peening

Laser-shock-peening technology is an international research hotspot in the surface-strengthening field, which utilizes the mechanical effects of laser-induced plasma shock waves to effectively improve the fatigue performance of metallic components by introducing the gradient microstructures and compressive residual stress into the surface layer of processed materials. The fatigue failure caused by high-frequency vibrations in aeroengines during service is the most important threat to flight safety, and this case is more prominent for military aeroengines because their service situation is harsher. The present paper focuses on components such as high-temperature components, fan/compressor blade, and thin-walled weldments, and it systematically introduces the researching findings about surface nanocrystallization and compressive residual stress formation mechanism in typical aeronautical metallic materials treated by laser shock peening. The contents mainly involve the characteristics, formation process, fatigue resistance mechanism, thermal stability of residual compressive stress, and nanocrystallization generated by laser shock peening.

Large Eddy Simulation of the Influences of the Pilot-Stage Structure on the Flow Characteristics in a Centrally Staged High-Temperature-Rise Combustor

Centrally staged combustion technique is often used in the military high-temperature-rise combustor. The pilot-stage structure affects the flow characteristics in the centrally staged combustor, which further affects the performance of ignition, combustion, and emission of military aero-engines. In order to increase the flow capacity of the swirler, the swirler with a non-rotating channel structure was designed. In this work, the influences of the pilot-stage structure on the flow characteristics in the centrally staged high-temperature-rise combustor are investigated. The flow fields of combustors with different pilot-stage swirl numbers (0.44, 0.60, and 0.71) are analyzed by large eddy simulation (LES). The results demonstrate that the primary recirculation zone (PRZ) becomes gradually longer and wider as the pilot-stage swirl number increases. In the combustors with three different pilot-stage structures, the precessing vortex core (PVC) was formed near the shear layer at the outlet of the pilot stage. The PVC frequency decreased from 1670 Hz to 1425 Hz and 1400 Hz with the increase of the pilot-stage swirl number from 0.44 to 0.60 and 0.71, respectively, and the breakdown position of the PVC shifted forward. The proper orthogonal decomposition (POD) and dynamic mode decomposition (DMD) methods are used to analyze the dynamic flow fields. It was observed that the corresponding frequency of the main pulsation structure decreased, and the flow instability was aggravated with the increase of the pilot-stage swirl number. The results deepen the understanding of the influences of the pilot-stage structure on the flow characteristics in the centrally staged high-temperature-rise combustor.

Research on Development Status and Trend of Aeroengine in China

The key manufacturing technology of aero-engine is an important index for the future development of aero-engine industry in China. The traditional manufacturing process and production mode can't meet the requirements of high precision, high quality, high efficiency and high reliability of aero-engine. The following three-axis, four-axis, five-axis digital processing is an important foundation for the future development of China aero-engine manufacturing industry. Aero-engine is the most important component of aircraft power supply system, and has experienced the development process of DC engine, brush synchronous engine and three-stage brushless synchronous engine. On the basis of analyzing the performance and characteristics of various engines, this paper analyzes the development direction of new civil and military aero-engines.

Application study on plasma ignition in aeroengine strut–cavity–injector integrated afterburner

To increase the thrust-weight ratio in next-generation military aeroengines, a new integrated afterburner was designed in this study. The integrated structure of a combined strut–cavity–injector was applied to the afterburner. To improve ignition characteristics in the afterburner, a new method using a plasma jet igniter was developed and optimized for application in the integrated afterburner. The effects of traditional spark igniters and plasma jet igniters on ignition processes and ignition characteristics of afterburners were studied and compared with the proposed design. The experimental results show that the strut–cavity–injector combination can achieve stable combustion, and plasma ignition can improve ignition characteristics. Compared with conventional spark ignition, plasma ignition reduced the ignition delay time by 67 ms. Additionally, the ignition delay time was reduced by increasing the inlet velocity and reducing the excess air coefficient. This investigation provides an effective and feasible method to apply plasma ignition in aeroengine afterburners and has potential engineering applications.

A novel low pressure-difference fluctuation electro-hydraulic large flowrate control valve for fuel flowrate control of aeroengine afterburner system

To address the control accuracy of large fuel flowrate during pressure fluctuation, a novel electro-hydraulic fuel metering unit (FMU) is constructed for afterburner fuel system of military aeroengine. Different from the previous FMU, the proposed FMU can achieve the higher precision opening control by a new metering valve with double control chambers (MVDCC), and realize the lower pressure difference fluctuation regulating by a novel two-stage constant pressure difference compensated valve (CPDCV) with dynamic damping orifice and damping piston. The experimental and AMESim simulation results verify the validity and superiority of the novel FMU. Since the temperature-induced variation in fuel properties and device capabilities may degrade or even impair the properties of novel FMU, the discharge flowrate is analyzed by global sensitivity analysis to research the effect proportion of each factor, the temperature effect is explored to ensure the working reliability in long-span temperature variation. Finally, the optimization of structure parameters for novel CPDCV can further reduce pressure difference fluctuation during pressure regulation, and the overshoot, adjust time and the integral of time multiplied by absolute value of error (ITAE) can be reduced by 24%, 30% and 26%, respectively. This paper provides a reference for improving the stability of large flowrate during pressure fluctuation.

Performance evaluation of a novel re-cooled mixed-flow turbofan cycle for aviation power application

A novel re-cooled mixed-flow turbofan cycle (RMTC) is proposed to meet the demand of high thrust-weight ratio for military aero-engine. Through adding a re-cooler during the compression process, the specific thrust can be improved by increasing the outer fan flow temperature and also the turbine cooling air consumption can be reduced by decreasing the inner fan flow temperature. This work conducts the modeling of ideal and actual RMTCs by using a verified original program. The effects of re-cooler location, heat transfer effectiveness, and bypass ratio on the specific thrust and fuel consumption rate are evaluated, and the RMTC performances in the entire flight envelope are discussed to estimate its applicable flight conditions. Based on the parametric analysis, locating the re-cooler after the compressor and increasing the heat transfer effectiveness are beneficial for the increase in specific thrust, while the effect of bypass ratio is related to the heat transfer capacity of re-cooler. The specific thrust improvement of RMTC is more significant at high flight Mach number, and hence, larger aircraft payload can be obtained with the same fuel mass. The assessment results show that the proposed RMTC system exhibits potential application for high-speed military aircraft.

Remaining Life Related Issues Being Pursued at DRDO for Indian Air Force

Abstract Hot section components of an aircraft gas turbine engine are critical to the performance and safety during the operation of military aircraft, where the service spectra are highly random and relatively severe in terms of the loading rates. DMRL, in collaboration with Indian Air Force (IAF), has initiated a project for the estimation of remaining life as well as life extension of military aeroengines of various origins. This is based on extensive laboratory specimen-level material characterization in terms of fatigue and creep, followed by the scale-up of experimental results to actual component. Finite Element Analysis (FEA) is an indispensable engineering tool for evaluation of the mechanical variables that determine crack initiation and growth, apart from material degradation prior to physical failure. DMRL's understanding and experience with FEA applications and damage mechanics concepts in these areas are briefly discussed in this paper.

A Novel Estimation Method on Delta Engine Gas Temperature of a Certain Aero-Engine Based on Flight Data

A novel estimation method on Delta Engine Gas Temperature (DEGT) applicable for condition based maintenance of a certain military aero-engine was proposed in this paper to solve the problem that maintenance technique for national military aero-engine relatively fell behind. The application perspective of this proposed method in the condition monitor of military aero-engine was also discussed. The experiment analysis on a group of actual flight data indicated that the DEGT obtained via the proposed method was matched to the actual degeneration performance of the aero-engine, which could well reflect the condition of the aero-engine.

Implications of Turbine Erosion for an Aero-Engine’s High-Pressure-Turbine Blade’s Low-Cycle-Fatigue Life-Consumption

Abstract Some in-service deterioration in any mechanical device, such as a military aero-engine, is inevitable. As a result of experiencing any deterioration, an aero-engine will seek a different steady operating point thereby resulting in a variation in the high-pressure spool speeds in order to provide the same thrust to keep aircraft’s performance invariant. Any increase in the high-pressure spool speed results in greater low-cycle fatigue damage for the hot-end components and thereby higher engine’s life-cycle costs. Possessing better knowledge (of the impacts of high-pressure turbine’s erosion upon the low-cycle fatigue life-consumption of aero-engine’s hot-end components) helps the users to take wiser management decisions. For a military aircraft’s mission profile, using bespoke computer simulations, the impacts of turbine erosion for high-pressure turbine-blade’s low-cycle fatigue life-consumption have been predicted.

Age-related maintenance versus reliability centred maintenance: a case study on aero-engines

Abstract Reliability Centred Maintenance (RCM) is a procedure carried out as part of the logistic support analysis (LSA) process and is described in the US Department of Defence Military Standards (Mil Std 2173). RCM allows logisticians the opportunity to determine the best maintenance policy for each component within a system. However, the only data that are available to carryout RCM using Mil Std 2173 are of MTBF. This implies that all the necessary mathematical models need to be based on the exponential distribution. This is a serious drawback to the whole concept of RCM as the exponential distribution cannot be used to model items that fail due to wear, or any other mode that is related to their age. In this paper, a new approach to RCM is proposed using the concepts of soft life and hard life to optimise the total maintenance cost. For simplicity, only one mode of failure is considered for each component. However, the model can be readily applied to multiple failure modes. The proposed model is applied to find the optimal maintenance policies in the case of military aero-engines using Monte Carlo simulation. The case study shows a potential benefit from setting soft lives on relatively cheap components that can cause expensive, unplanned engine rejections.

Analysis and modeling of the creep behavior of the thermostable PMR-15 polyimide

To establish the constitutive equations for carbon/PMR-15 composites and to determine the contribution of the matrix to the mechanical response, an analysis of the behavior of the PMR-15 polyimide alone has been performed under thermomechanical loading conditions corresponding to military aeroengine applications. In particular, the creep behavior of the material has been studied for several combinations of stress (0.3 to 0.7 σr), temperature (250 to 300°C), and time (5 and 1300 h). The creep compliance has been modeled in the field where the behavior is linear, using the Bürgers model, together with a retardation time distribution for the viscoelastic region. The viscoelastic behavior is described satisfactorily by the Kohlrausch function, and combined with the Maxwell relation, enables the creep compliance of PMR-15 polyimide to be modeled in the temperature range considered for short loading times. For long times at 250°C and 0.3 σr, the polymer undergoes slow plastic deformation, but nevertheless, conserves its overall viscoelastic properties. There is no equivalence between time and temperature. The master curve, constructed graphically on the basis of linear viscoelastic strains, short times, and a reference temperature of 250°C, deviates quite significantly from the experimental curve at longer times. In the latter case, the creep compliance curve can be correctly fitted to a simple power law. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 1983–1991, 1998

The United Kingdom Engine Technology Demonstrator Program

It is generally accepted that development time scales for civil and military aero-engines can exceed those of the airframe they will power. It is now essential to ensure that relevant engine technologies are conceived and proven ahead of commitment to full-scale engine development if future military and civil propulsion requirements are to be met in an affordable way. The scope and scale of UK demonstrator activity has been greatly expanded in recent years in recognition of this need, principally through increased government funding. This paper discusses the principles underlying technology demonstration including the circumstances pertaining in the UK, concluding that a comprehensive program of technology demonstration conducted in a step-by-step fashion and properly integrated with transition to full-scale engineering development will produce significant financial and operational benefits.