Bypass Duct Research Articles

Performance analysis of the adaptive cycle engine with cooling air: From propulsion performance, thermodynamic efficiency, exergy and infrared characteristics

The adaptive cycle engine gains significant attention due to its variable thermodynamic cycles and multi-duct characteristics, which are utilized for thermal management to enhance engine performance. This paper explores the features of multi-duct technology in adaptive cycle engines and aims to improve engine flight performance. An analysis is conducted on the impact of duct air bleed on engine propulsion characteristics, thermodynamic cycle properties, and exhaust system infrared radiation characteristics. Initially, a component-level model of the adaptive cycle engine was established, considering CDFS duct, bypass duct, and third duct air cooling devices. This model uses the ducted cold air to cool the temperature of low-pressure turbine exit, center cone wall, and main nozzle expansion section wall. Subsequently, a method for analyzing the infrared radiation of the engine exhaust system was proposed based on the above model, and the performance of engine components and the overall engine was analyzed in terms of energy, exergy, mechanical efficiency, and thermal efficiency. Finally, the numerical simulations of the propulsion performance, thermodynamic efficiency and infrared characteristics of the adaptive cycle engine with cooling air were carried out under conditions of ground takeoff, subsonic cruise, and supersonic cruise. The simulation results show that the cooling air can effectively enhance engine performance and infrared stealth capabilities under various flight conditions. The ducted air extraction measures proposed in the paper could effectively improve the propulsion efficiency and stealth characteristics of the engine, providing important references for the development of more efficient aeroengine.

Synergetic and Performance Characteristics of A High-Speed Pre-Cooled Propulsion Concept

Abstract Pre-cooled air-breathing cycles are promising candidates to power future high-speed flight as well as Single-Stage-To-Orbit vehicles, due to their increased efficiency over contemporary propulsion systems and launch vehicles. These concepts usually feature complex interactions in the synergy of their thermodynamic cycles. In this study, a performance model of such a cycle is developed for its air-breathing mode of operation. One-dimensional thermodynamic modeling is employed within a component-level approach, to evaluate the performance and operation of the cycle under investigation in the range of 1.35 = ≤ 8 = 5 and conditions of up to 26 kilometers altitude. The model is validated quantitatively and qualitatively for both design and off-design conditions. The specific impulse Isp and specific thrust, as predicted by the model, agree within less than 5% for both design and off-design point conditions, while it captures the trend of Isp for the range modeled. Moreover the maximum gross thrust point is predicted correctly at M∞ = 4. The fundamental operating principles and synergetic characteristics of the engine at design and off-design conditions are investigated and reported. A model which does not feature a bypass duct is created and compared for the same inflow conditions and mission profile. It is found that the engine without the bypass duct exhibits reduced specific impulse up to 32% lower at off-design conditions while the overall trend of engine efficiency cannot be properly captured without modeling of the bypass duct, especially at the region of M∞ < 3.5.

Reverse Thrust Aerodynamics of Variable Pitch Fans with Inlet Distortion

Abstract Variable pitch fans can improve the operability of low pressure ratio fan systems by re-pitching the rotor blades. If a variable pitch fan can generate sufficient reverse thrust on landing it also eliminates the need for heavy, cascade-type thrust reversers. However, any reverse thrust generation is impacted by high levels of inlet distortion generated as air is drawn into the exhaust nozzle. This paper uses RANS computations and low-speed rig experiments to explore how a representative inlet distortion from the engine installation affects the aerodynamics and performance of a variable pitch fan operating in reverse thrust mode. The simulations and the experiments show that the distortion from the engine installation leads to a highly three-dimensional flow field with a large recirculation region within the bypass duct. The distortion substantially redistributes the mass flow, thrust and power in the engine. Streamline tracking combined with a power balance analysis reveals highly radial flow within the fan rotor, with almost all the fan power used to drive the recirculating flow in the bypass duct, generating high loss and high total temperature. The recirculation reduces the net mass flow through the engine to around 5% of a uniform inflow case and greatly reduces the effective reverse thrust. With uniform inflow, the net reverse thrust was found to be 35% of the nominal takeoff thrust. With inlet distortion, this was reduced to 20%. This demonstrates the importance of designing and operating variable pitch fan systems to minimise reverse thrust inlet distortion.

Effects of distortion on a BLI fan

Abstract The BLI (boundary layer ingestion) concept for propulsion seeks to improve the energy efficiency of aircraft propulsion. This is achieved by accelerating low momentum flow ingested from boundary layers and wakes developed over the fuselage through the fan. A major challenge that needs to be overcome to realise the benefits is that the fan needs to work efficiently in distorted flow. Understanding the effects of distortion on the aerodynamic performance and the distortion transfer through the fan is therefore essential to future designs. A BLI fan, designed at reduced scale, is used for analytic modelling and experiments in a rig designed for this purpose. The test rig replicates BLI conditions for a fan installed at the aircraft tail cone. An unsteady model that includes all blades and vanes of the fan, as well as the nacelle and the by-pass duct of the test rig is used for CFD (computational fluid dynamics) simulations. Test results are used to confirm that the CFD model is representative of the aerodynamics of the fan. The tests are conducted using varying fan operating conditions but also tests with an added distortion screen. Analysis results are then used to investigate the effects of distortion on the fan efficiency, as well as on the overall efficiency. The fan efficiency is found to be moderately decreased depending on the level of and extent of inlet circumferential distortion. In terms of overall energy efficiency, a net improvement over a similar fan in clean inlet flow is found.

Performance evaluation of multicombustor engine for Mach3+-Level propulsion system

Turbine-based combined cycles are widely considered as a propulsion system for hypersonic vehicles. The inadequate performance of turbine-based engines has resulted in thrust traps, thereby limiting the development of turbine-based combined cycles. To satisfy the performance requirements over a wide speed range, a novel Mach 3+-level multicombustor engine is proposed, and its performance potential is investigated, where an intermediate bypass burner reheats the core airflow to generate more cycle work and the second bypass duct heated by a bypass afterburner provides the main source of the engine thrust at high Mach numbers. Results show that the multicombustor engine extends the flight envelope from Mach 2.5 to 3.5 and increases the thrust by 32% compared with the conventional engine. The application of an intermediate bypass burner reduces the turbine pressure ratio by 43%, thereby reducing the number of turbine stages. The concept of a multicombustor engine is promising for designing the power systems of hypersonic vehicles.

Research on high fidelity modelling and optimum designing of an adaptive cycle engine's starting process

An adaptive cycle engine is an evolutional aero-engine that can achieve low fuel consumption and high efficiency by adjusting the thermodynamic cycle; however, few studies have been conducted on adaptive cycle engine performance at low speeds. A high-fidelity ground starting model of an adaptive cycle engine is established by correcting the low speed characteristics of the components, while considering the effects of rotor inertia, volume, combustion efficiency, and the thermal inertia of the combustor and turbine. By employing a physically enhanced prediction method, three operating states of the compressor at low speeds are obtained: compressor, stirrer, and turbine state. The matching mechanism of the adaptive cycle engine and the detailed influence of the variable geometries on the engine's performance during the starting process are explored. The study shows that the third bypass duct has little effect on the engine starting time, and opening the mode select valve can reduce the starting time. Compared with the initial settings, the starting time decreases by 3.98 s after optimization with the variable geometries. The detailed impact of the variable geometries on the engine's starting performance provides an engineering reference value for the control strategies.

Effect of Bypass Duct on the Thrust Vectoring Performance of Dual Throat Nozzle in a Supersonic Aircraft

Abstract Due to its ability to maximize thrust vectoring performance, the bypass dual throat nozzle (BDTN) has an advantage over other fluidic vectoring controls. In this study, numerical simulation is performed to analyze the flow characteristics and performance parameters of an aircraft engine with three different nozzle configurations. The nozzle of a representative engine, i.e., an F100 engine was selected as a model geometry to test the efficiency obtained by BDTN. The present investigation has shown that implementing a bypass channel on a real geometry nozzle has no significant effects on thrust vectoring performance in vectored mode. Although the real geometry scheme has a higher thrust and a discharge coefficient, the smaller cavity length resulted in lower vectoring angles. Modifying the real geometry nozzle according to the BDTN configuration significantly improved the thrust vectoring performance. However, the V-shaped bypass passage flow in the modified geometry scheme imposed un-necessary total pressure losses in the nozzle. A geometry scheme that utilized an arc-shaped rather than a V-shaped bypass passage is considered in this research and found to present minimize pressure losses. A total increase of 2% and 3.5% is hereby reported, for thrust and discharge coefficients, respectively. A decrease of 6% is reported in the thrust vectoring angle under an improved geometrical scheme. Out of three geometries, the real geometry scheme reported negligible thrust vectoring performance, while modified and improved geometry schemes indicated improved thrust vectoring performance without substantially changing the engine states.

Machine Learning Aided Low-Order Predictions of Fan Stage Broadband Interaction Noise

A fast method for predicting turbofan fan-stage broadband interaction noise is being developed. The downstream propagating acoustic power in the bypass duct due to the response of the fan exit guide vane (FEGV) to fan wake turbulence is computed based on two-dimensional flat-plate cascade analysis and Green’s method. This study focused on using machine learning to define the fan wake parameters used as inputs to the FEGV response and noise calculation. Machine-learning algorithms are being trained using computational fluid dynamics results. This paper describes the accuracy of machine learning given the available rotor wake data. Further, the effect of errors in the learned input data on the acoustic prediction was studied. Based on this study, the method shows great promise.

Investigation of overall performance of turbofan engine with pulse detonation combustor in bypass duct

The performance model was established to study the performance of mixed exhaust turbofan engine with pulse detonation combustor (PDC) in the bypass duct. The effects of the total pressure loss of isolator and bypass circulation parameters on the characteristic of PDC and performance of engine were analyzed. Then, the sensitivity analysis of performance parameters was carried out on the influence of the components parameters. The performance of mixed exhaust turbofan engine with PDC in the bypass duct was compared with that of the conventional afterburner turbofan engine at the same design circulation parameters. The results show that to increase the total pressure loss of isolator is beneficial to the improvement of performance because of the improvement of pressure ratio; when fan pressure ratio is constant, with the increasing of bypass ratio, the specific fuel consumption and specific thrust increase; with the increasing of fan pressure ratio, when bypass ratio is 0.2 to 0.4, specific thrust increases first and then decreases. When bypass ratio is 0.4 to 0.5, specific thrust increases first and then remains constant. When bypass ratio is 0.5 to 0.9, specific thrust increases, but the rate of increase reduces. At different bypass ratio, specific fuel consumption decreases with increasing of fan pressure ratio; the performance of engine is more sensitive to the component parameters that directly affect the flow state parameters of the bypass duct; because of supercharging performance of PDC, PDC in the bypass duct only uses part of air flow to organize combustion that can make specific thrust of turbofan engine with PDC in the bypass duct and conventional afterburner turbofan engine are equivalent. Meanwhile, specific fuel consumption can be reduced by 27.7% at design point and 12.8%-26.8% at off-design points.

Outdoor engine test using acoustic liners combined with Fine-Perforated-Film

Resonant-type liner panels are one the primary countermeasures for the fan noise of aircraft engines, though the noise reduction performances of the liners are known to be tolerated by the flow streaming on the liner surface. Therefore, suppressing the effect of the flow on the liners is greatly important for larger noise reduction. In this study, a liner panel with a special surface structure was manufactured and applied to an outdoor test using a small turbofan engine, DGEN 380. The surface structure consisted of a special thin film, Fine-Perforated-Film (FPF), and a gap. The gap was fixed between the FPF and liner surface. In addition, a typical resonant-type liner and a hard wall were used for comparison, to investigate the effect of the structure. During the test, the samples were installed to the exhaust bypass duct of the DGEN 380 engine. The acoustic pressure was measured with a far field microphone array. Analysis and comparison of the results showed that the new structure suppressed the effect of the grazing flow and caused a larger amount of noise reduction, compared to the typical liner sample.

Body Force Modeling of the Fan Stage of a Windmilling Turbofan

Abstract The determination of the rotational speed and massflow of the fan of a turbofan at windmill is critical in the design of the engine-supporting structure and the sizing of the vertical stabilizer. Given the very high bypass ratio obtained at windmill, the flow in the fan stage and bypass duct is of prime interest. Classical computational fluid dynamics simulations have been shown to predict such flows accurately, but extensive parametric studies can be needed, stressing the need for reduced-cost modeling of the flow in the engine. A body force modeling (BFM) approach for windmilling simulations is examined in the present contribution. The BFM approach replaces turbomachinery rows by source terms, reducing the computational cost (here by a factor 6). A shaft model is coupled to the BFM source terms, to drive the simulation to a power balance of the low-pressure shaft. The overall approach is thus self-contained and can predict both the massflow and the rotational speed in the windmilling regime. Comparisons with engine experimental results show the proposed model can predict the rotational speed within 7%, and the massflow within 5%. Local analysis and comparisons with experimental data and reference blade calculations show that the work exchange, in term of total temperature variation, is predicted within 0.5 K, and the overall total pressure ratio within 1%. However, the losses in the stator are largely underestimated, which explains the discrepancy for the massflow predictions.

Aerothermal characterization of finned surfaces in high-speed flows

Surface Air Cooled Oil Coolers are finned heat exchangers installed in the bypass duct of a turbofan engine that act as an additional cooling source for the engine components, having transonic flow as a heat sink. Characterizing the heat transfer and the aerodynamics of finned surface designs is essential to understanding their impact on overall engine efficiency. In the present study, different models are assessed numerically and experimentally. Two geometries are tested in a high-speed linear wind tunnel where measurements are taken using several sensors and optical techniques. An Inverse Heat Conduction Methodology based on a Levenberg-Marquardt Algorithm is developed to retrieve the heat flux on the fin’s surfaces accurately. A numerical analysis is performed using Reynolds Averaged Navier-Stokes simulations, and the results are compared against the experimental findings. A good agreement is observed between the datasets supporting the accuracy of the numerical methodology. Finally, a multi-objective optimization algorithm is coupled with the solver to explore new geometries that maximize the heat transfer while minimizing the pressure drop across the studied domain. Over 400 profiles were generated and numerically analyzed, allowing for identifying the features that have a more decisive influence on the performance of the fins. Profiles that present improvements of up to 19% are selected and analyzed in further detail. A combined improvement of 7.5% heat transfer enhancement and 9.1% reduction in pressure losses is achieved while maintaining a constant mass flow.

Starting and windmilling simulations using compressor and turbine maps

Starting and windmilling simulations with a normal gas turbine performance program require extended compressor and turbine maps which include sub-idle corrected speeds down to say 5–10% of the design value. During such simulations certain specific phenomena which are insignificant in the normal operating range between idle and full power must be considered. For example, while starting a low bypass ratio mixed flow turbofan, flow reversal in the bypass duct can occur. This paper illustrates a general understanding of what happens from when the starter is activated to when stabilized idle operation is reached. Operating lines in the compressor and turbine maps are predicted depending on starter torque, starter power, burner light-up and starter cut-off speed. It is explained why knowing combustor efficiency precisely is not required for that. Simulating engine starting and windmilling is not a magical art. The laws of physics still apply at these somewhat exotic operating conditions.

The Use of Uncertainty Quantification and Numerical Optimization to Support the Design and Operation Management of Air-Staging Gas Recirculation Strategies in Glass Furnaces

The reduction in energy consumption and the increasingly demanding emissions regulations have become strategic challenges for every industrial sector. In this context, the glass industry would be one of the most affected sectors due to its high energy demand and emissions productions, especially in terms of NOx. For this reason, various emission abatement systems have been developed in this field and one of the most used is the air staging system. It consists in injecting air into the upper part of the regenerative chamber on the exhaust gases side in order to create the conditions for combustion that reduces NOx emissions. In this work, the combined use of CFD with data analysis techniques offers a tool for the design and management of a hybrid air staging system. Surrogate models of the bypass mass flow rate and uniformity index in the regenerative chamber have been obtained starting from DoE based on different simulations by varying the air mass flow rate of the two injectors located in a bypass duct that connects the two regenerative chambers. This model allows a UQ analysis to verify how the uncertainty of the air injectors can affect the bypass mass flow rate. Finally, an optimization procedure has identified the optimal condition for the best bypass mass flow rates and uniformity of the oxygen concentration in the chamber. High values of the mass flow rate of the pros injector and medium-low values for the cons injectors are identified as operating parameters for best conditions.

Fan Noise Reduction by Acoustic Liners Combined with Fine-Perforated-Film: Noise Tests by a Small Turbofan Engine DGEN 380

Resonant-type liner panels are one the primary countermeasures for the fan noise of aircraft engines, though the sound absorption performances of the liners are known to be tolerated by the grazing flow streaming on their surface. Therefore, suppressing the effect of the flow on the liners is greatly important for higher sound absorption efficiency. In this study, liner panels with special surface structures were manufactured and applied to an outdoor test using a small turbofan engine, DGEN 380. A special thin film, Fine-Perforated-Film (FPF), was applied to two liner samples. In the first sample, FPF was applied directly to the surface of a typical liner. In the second sample, a gap was fixed between the FPF and liner surface. In addition, a rigid wall and a typical liner were used for comparison, to investigate the effect of the structures. During the test, the samples were installed to the exhaust bypass duct of the DGEN engine. The acoustic pressure inside the duct and in far field was measured. Analysis and comparison of the results showed that the new structures suppressed the effect of the grazing flow and caused a larger amount of noise reduction, compared to the typical liner sample.

Способ оценки адекватности результатов численного моделирования поля параметров неравномерного потока на входе в вентилятор ТРДД экспериментальным данным

The article substantiates the need to intensify the process of oil cooling in the oil systems of aircraft turbojet engines. Currently, an increase in the thrust of turbojet engines is achieved by increasing the air pressure ratio in the compressor and the gastemperature in front of the turbine. However, an increase in thevalues of theseparameters leads to an increase inthe thermal loadof theengine elements,including rotor supports, which causes an increase in oil temperature. The oil systems of modern turbojet engines still use the same oils as several decades ago.Therefore, the intensification of the oil cooling process, which allows reducing its temperature, is the main way to preserve the lubricating properties.It is proposed to intensify the oilcooling process in the oil system of the bypass turbojet engine byinstalling an air-oil heat exchanger in the bypass duct.A thermal calculation of fuel-oil and air-oil heat exchangers has been carried out, the results of which show large values of the heat transfer coefficient when the oil is cooled by the bypass duct air

Intensification of oil cooling by installing an air-oil heat exchangerin the bypass duct of a bypassturbojet engine

Intensification of oil cooling by installing an air-oil heat exchangerin the bypass duct of a bypassturbojet engine

Development of Translucent Design Philosophy for the Cyclic Pattern Design of Fan Outlet Guide Vanes

Abstract The fan systems of typical high bypass civil engines encounter strong flow distortions originating in the intake and the bypass duct. These flow distortions cause the fan stage operation point to vary from its design intent, thus reducing the fan stage performance and increasing low engine-order fan blade forcing. A cyclic pattern design for the fan Outlet Guide Vanes (OGV) can be effectively used to recover the fan stage performance and to control its system-level aeromechanical behavior. This paper presents the development of an OGV pattern design philosophy using the numerical experimentation technique. Multiple fan-intake unsteady computational fluid dynamic computations are conducted by clocking the circumferential pressure profile at the fan exit. The study revealed that a mild, low-harmonic fan back pressure profile with a suitable clocking position is able to improve the fan rotor efficiency and reduce the first engine order (1EO) fan forcing simultaneously. Such a profile can be generated by designing a cyclic OGV pattern that allows the bifurcation potential fields of controlled intensity and phase to pass through the OGV blade row, thus termed the translucent design philosophy. Further, a sensitivity study is performed to assess the effects of simultaneous distortions upstream and downstream of the fan. The study showed that a correctly clocked intra-stage static pressure profile can consistently improve both the performance and aeromechanical behavior of fan systems having different intake lengths and at different flight conditions. The implementation of the proposed translucent design philosophy in a new OGV pattern design tool is discussed.

Numerical study of the effect of flow nonuniformities on the low-pressure side of a Cooled Cooling Air heat exchanger

The Cooled Cooling Air (CCA) heat exchanger is a precooler that cools the bleed air from the compressor stages and is located inside the bypass duct of the aeroengine. Nonuniform flows enter the core of the heat exchanger because the cold side is the off-take from the fan flow, compromising its aerothermal performance. These aspects has been disregarded in the literature until now. In this study, the aerothermal performance of a CCA heat exchanger with flow nonuniformities on its Low-Pressure (LP) side is investigated. Three-wire meshes were designed using correlations from the literature, showing three off-design cases, namely, Cases 1, 2, and 3. The porous media and dual cell heat exchanger models were used in numerical simulations for the baseline and off-design cases. Experiments were performed at hot and cold conditions to validate the numerical simulations under actual gas turbine operating conditions. It has been found that heat transfer rate increases in Case 1 and 2 by 1.0% and 1.5%, as the flow non-uniformity is symmetric with respect to XZ plane. In contrast, in Case 3, the heat transfer rate reduces by 4.2% because the flow non-uniformity is asymmetric with respect to XZ plane, inducing cross-flows immediately upstream of the heat exchanger core. • Aerothermal performance with flow nonuniformities along LP side was investigated. • The porous media and dual cell heat exchanger models were used. • Experiments were performed under actual gas turbine operating conditions. • The overall heat transfer rates were improved by 1.0% and 1.5% in Cases 1 and 2. • The overall heat transfer rate declined by 4.2% in Case 3.

Recognizing the aeroacoustic information of noise radiated by an unflanged duct based on convolutional neural networks.

Accurately recognizing the aeroacoustic information of noise propagating into and radiating out of an aero-engine duct is of both fundamental and practical interest. The aeroacoustic information includes (1) the acoustic properties of the noise source, such as the frequency (f) and the circumferential and radial mode numbers (m, n), and (2) the flight conditions, including the ambient flow speed (M0) and the jet flow speed (M1). In this study, a data-driven model is developed to predict the aeroacoustic information of a simplified aero-engine duct noise from the far-field sound pressure level directivity. The model is constructed by the integration of one-dimensional convolutional layers and fully connected layers. The training and validation datasets are calculated from the analytical model for noise radiation from a semi-infinite unflanged duct based on the Wiener-Hopf method. For a single-spinning mode source, a regression model is established for f, M0, and M1 prediction, and a classification model is built up for m and n prediction. Additionally, for a multi-spinning mode source, the regression model is used to predict the coefficient of each mode. Results show that the proposed data-driven model can effectively and robustly predict the acoustic characteristics of noise propagation in and radiation out of an aero-engine bypass duct.