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Based on the transient-performance calculation model of a dual-spool mixed-flow turbofan engine, this article improves the dynamic algorithm of geometric adjustment mechanisms and establishes a transient-performance calculation model suitable for a three-stream adaptive cycle engine (three-stream ACE). Using this model, the transient characteristics of a three-stream ACE were analyzed. The results indicate that the delay in the area of the fan nozzle significantly reduces the surge margin of the front fan during deceleration, while the delay in the angle of the front-fan and aft-fan guide vanes significantly reduces the surge margin of the front fan during acceleration, therefore becoming a limitation of the transient performance of the engine. At the same time, to meet the demand for equal-thrust mode switching, this article also proposes a mode-switching control scheme that solves the problem of engine state oscillation during the mode-conversion process and achieves a smooth conversion with thrust fluctuations within 1%. The research results of this article can guide the optimization design of three-stream ACE transition-state control laws and the design of control system architecture, which has important engineering significance.

Mode transition is an important dynamic process of an adaptive cycle engine (ACE). In order to obtain a smooth mode transition process, the closed-loop controller is designed based on the strong robust augmented linear quadric regulator (ALQR) method, and with the objective of minimizing the thrust fluctuation in the process of mode transition, an open-loop geometrical mechanism control schedules optimization method based on Bézier curves is proposed, so that the closed-loop control and the open-loop control can work in coordination. The simulation results at the subsonic cruise operating point and supersonic cruise operating point show that based on the optimized open-loop geometrical mechanism control schedules and the designed closed-loop ALQR control system, the ACE achieves fast and smooth geometrical mechanisms and engine output transition during the mode transition process with a maximum thrust fluctuation of 2.58%, which is much smaller than that of the traditional linear variation geometric mechanisms with a maximum 4.64% thrust fluctuation, which verifies the effectiveness of the proposed control method.

The operation range of the adaptive cycle engine (ACE) compression system is constrained by both the compression components and the bypass ducts, resulting in intricate matching mechanisms. Conventional analysis methods struggle to adequately evaluate the feasible operating range or the coupled constraints between components. This study employs an integrated hybrid-dimensional approach, combining zero-dimensional bypass analysis with one-dimensional/quasi-two-dimensional component analysis, to systematically investigate the matching effects of a triple-bypass compression system. The influence of key matching parameters, including the compression component operating points, high-pressure (HP) and low-pressure (LP) shaft speeds, and the core-driven fan stage (CDFS) variable inlet guide vane (VIGV) angles, is investigated. Results indicate that compression component matching primarily influences adjacent downstream bypass ratios, while HP/LP shaft speeds and the CDFS VIGV angle predominantly regulate the first and second bypass ratios. The feasible operating envelope is determined by the superimposed effects of these control parameters. To maximize the total bypass ratio, optimal operation requires increasing the front fan stall margin, elevating LP shaft speed, reducing HP shaft speed, and implementing partial CDFS VIGV closure to enhance pre-swirl. These findings provide critical guidance for control logic refinement and design optimization in advanced variable-cycle compression systems.

The adaptive cycle engine (ACE) is considered a crucial candidate for the propulsion systems of next-generation aircraft. Its high thrust and low fuel consumption operating modes make it suitable for various flight missions. However, the complex couplings and novel components in the ACE pose significant challenges to its performance design. This paper presents a systematic literature review on development status and performance deign of ACEs. Firstly, the development of ACE at various periods over the past few decades is presented. Then, four typical ACE configurations are introduced and analyzed based the differences of the core and the low-pressure compression system. After that, an emphasis is placed on the performance optimization method for ACE under various operating conditions, including steady-state, mode transition, acceleration/deceleration, and considering uncertainties. In addition, the numerical zooming technology for non-rotating components, rotating components, as well as intake and exhaust system are summarized in this paper. Through the above summary and analysis, the development trends in ACE performance design are explored.

Centrifugal compressors are widely used in gas turbines, so it’s important to have an efficient performance; also, optimizing this part can affect the whole engine’s performance. Adaptive Cycle Engines (ACEs) are a group of gas turbine engines that can change key aerodynamic parameters such as pressure and bypass ratio through geometric structure adjustment. In the present research, the ACE with a centrifugal compressor as its high-pressure compressor (HPC) is investigated, and the aim is to improve the engine performance through compressor optimization. A three-dimensional surrogate-assisted aerodynamic optimization method is applied to maximize the isentropic efficiency of the centrifugal compressor with a constraint on the total pressure ratio. The optimization results show a 3.4% improvement in the design point efficiency, a 1.4% increment of the choked mass flow rate, and a wider operating range is obtained. Afterward, thermodynamic modeling of the engine performance is used to calculate the engine characteristics before and after the optimization. 3D performance maps of the compressor and fan, calculated by CFD simulation, are used for accurate engine performance modeling. The final results of the engine performance show a reduction of 2.0% in the specific fuel consumption of the improved engine, which is an important achievement in these engines.

This study investigates the adaptive cycle fan (ACF), a key component enabling variable-cycle functionality in next-generation adaptive cycle engines (ACE). Despite its critical importance for whole-engine matching, the full operating-range performance of the ACF and the coupling effects among its parameters have not been systematically examined. This work addresses this gap. Owing to its dual-flowpath architecture and multiple adjustable variables, advanced modeling approaches are required; therefore, a neural-network-based surrogate model is developed to map parameter variations to ACF performance. Based on this model, the full operating-range performance of the ACF is analyzed. The constant-speed performance forms multi-line surfaces with distinct trends across rotational speeds. Core throttling provides wide-range total pressure ratio regulation, while bypass throttling enables broad bypass ratio modulation with relatively stable pressure ratio and efficiency. To interpret the neural network, the SHAP method is employed to quantify parameter sensitivity and multi-parameter coupling effects. Bypass outlet backpressure, core outlet backpressure, and front-fan tip clearance are identified as dominant factors, exhibiting strong coupling effects that must be jointly considered for optimal engine regulation. This study presents the first three-parameter coupling analysis of an ACF and provides guidance on ACE control design, component matching, and adjustable structure design.

In the process of studying the steady-state performance and component matching of adaptive cycle engines with convertible fan system, it was found that the front fan and aft fan stage have a unique matching problem when the mode select valve is closed and engine is operating at higher Mach number conditions. The cause of this matching problem was studied with numeric simulation in this paper. Based on the features of adaptive cycle engines with convertible fan system, the possible methods and their feasibilities of solving this matching problem were also discussed. According to the results, the flow rate adjustment capacity of the aft fan stage directly determines the occurrence and severity of this matching problem. The matching problem can be ameliorated in some extent by either reducing the design second bypass ratio or adjusting the variable geometry mechanisms, but it cannot be completely solved at the aspect of component matching mechanism.

The most remarkable variable cycle characteristic of the variable cycle engine (VCE) is that it keeps airflow almost constant during subsonic cruise throttling by modulating variable geometries, which can efficiently decrease spillage drag and increase installed thrust. One of the most critical challenges for the modulation lies in completely maintaining airflow, as well as avoiding specific fuel consumption (SFC) degradation during throttling. This has resulted in a need to investigate the modulation regulation of the adaptive cycle engine (ACE) which is a new concept for VCE and has greater potential for flexibly modulating airflow and pressure ratio. Thus, the aim of this paper is to study the variable geometries’ modulation schedule of ACE in maintaining airflow during throttling. A configuration of an ACE concept and its modeling study are first put forward. Then, the control schedule is researched via the combination of sensibility analysis and basic working principle instead of optimizing them directly. Results show that when the net thrust decreases from 100% to about 55% during subsonic cruise and to 32% during the supersonic cruise, the demand airflow of the engine is kept almost constant, which greatly improves the installed performance during throttling.

The adaptive cycle engine (ACE) can modulate thermal cycle characteristics by adjusting variable geometry components, enabling rational distribution of bypass flow rates. As a key component of the ACE, the rear variable area bypass injector (RVABI) significantly influences the engine bypass ratio and consequently alters engine performance. RVABIs are typically categorized into three configurations based on their design: Translation Type, Rotary Type, and Hole Type. Previous studies have not fully elucidated the overall operating characteristics, internal flow mechanisms, and applicable scenarios of these different RVABI configurations. To address this problem, this paper first introduces and validates a three-dimensional (3D) simulation methodology for RVABIs. Subsequently, criteria for reasonably evaluating the operating characteristics of different RVABI configurations are defined. Following this, the differences in operating characteristics and internal flow mechanisms among the three RVABI configurations are systematically compared. Finally, the application scenarios for each configuration are identified. This work provides valuable insights to guide the configuration selection and parameter design of RVABIs in practical engineering applications.

In the overall design process of the turbofan engine, it has become crucial to address the challenge of selecting design parameters that not only meet the flight thrust demand but also enhance engine economy. As the demand for stealth performance in future fighter aircraft increases, it becomes imperative to consider infrared stealth indicators during the design process. The adaptive cycle engine possesses an adjustable thermal cycle, necessitating careful attention to the selection of design parameters to fulfill the requirements. Therefore, this paper proposes a multi-objective optimization design method for the adaptive cycle engine that integrates infrared stealth technology. Initially, the parameter cycle model of the adaptive cycle engine is established based on the principles of aerodynamic and thermodynamic calculations. Subsequently, the model incorporates a serpentine two-dimensional (2-D) exhaust system to achieve infrared suppression. Meanwhile, a method for predicting the infrared characteristics is proposed to calculate the infrared radiation intensity of the engine exhaust system. Finally, the sequential quadratic programming algorithm is applied to comprehensively optimize the engine’s performance. The simulation results reveal that the multi-objective optimization design can effectively select appropriate design parameters to im-prove the engine, thereby reducing fuel consumption while meeting thrust requirements. This approach combines the consideration of infrared stealth technology with the optimization of engine performance, thus contributing to the development of advanced adaptive cycle engines.