High Bypass Ratio Turbofan Engine Research Articles

Design and Numerical Analysis of an Annular Combustion Chamber

Designing a combustion chamber for gas turbines is considered both a science and an art. This study presents a comprehensive methodology for designing an annular combustion chamber tailored to the operating conditions of a CFM-56 engine, a widely used high bypass ratio turbofan engine. The design process involved calculating the basic criteria and dimensions for the casing, liner, diffuser, and swirl, followed by an analysis of the cooling sections of the liner. Numerical simulations using NUMECA software and the HEXPRESS meshing tool were conducted to predict the combustion chamber’s behavior and performance, employing the κ-ε turbulence model and the Flamelet combustion model. Methane was used as the fuel, and simulations were performed for three fuel injection angles: axial, 45°, and 60°. Results demonstrate that the combustion chamber is properly dimensioned and achieves complete combustion for all configurations. The pressure ratio is 0.96, exceeding the minimum design criteria. Additionally, the emissions of unburned hydrocarbons are zero, while nitrogen oxides and carbon monoxide levels are below regulatory limits. These findings validate the proposed design methodology, ensuring efficient and environmentally compliant combustion chamber performance.

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).

Air-Ground Characteristic Test and Analysis on Fan Blade Vibration Stress of Turbofan Engine

Obtaining the vibration stress of fan rotor blades under actual working conditions through flight tests is a necessary means to carry out design verification and optimization improvement of turbofan engine. Taking the high bypass ratio turbofan engine as research object, installed ground and flight tests were carried out. The vibration characteristics and stress distribution of the fan blade were obtained by direct measurement means of strain gauge, and the air-ground characteristics of the test data were compared and analyzed. The results show that under the steady state, the vibration stress level of fan blade in ground test is significantly higher than that in flight test; There is a significant difference in frequency distribution of excitation factors on fan blade in the ground and flight tests.

Development trends and future expectations of jet engine

Nowadays, nearly all large commercial aircraft are powered by gas turbine engines. Having been developed for about 80 years of engines applied on commercial aircraft, from low bypass ratio turbojet engines to high bypass ratio turbofan engines since the first turbojet engine was patented in 1930 by Frank Whittle, gas turbine engines still have a high potential to improve the performance. Currently, motor thermodynamic efficiency can still rise in the following decades; composite materials, for instance, gamma titanium aluminum and polymer matrix composites, are becoming widely used in airliner propulsion due to their lightweight and high-temperature capability. Accordingly, environmental issues related to gas emissions have also become vital due to the continued flourishing of commercial airliners. In this paper, the development of gas turbine engines applied on commercial airliners from low bypass ratio turbojet engine "Nene1" to high bypass ratio turbofan engine "GE9X," and the current advancement of jet engines applied will be discussed in order to gain possible improvement on the performance of jet engines. Current conditions and expectations of jet engines will be discussed with specific examples, focusing on efficiency, materials and manufacturing, and environmental issues. In the paper, the engines mentioned are all related to commercial aircraft.

Nacelle intake flow separation reduction at cruise condition using active flow control

Turbofan engine intakes are designed to provide separation-free flow at the fan face over a wide range of operating conditions. But at some off-design conditions, like at high flight speeds and high angles of attack (AoA), the aero engine intake may encounter flow separation. This boundary layer separation inside the nacelle inlet of an aircraft engine can lead to a large number of undesirable outcomes like reduction in fan efficiency, engine stall and high levels of stress on the fan blades. Active flow control is a promising solution to reduce inlet boundary layer separation and the associated fan-face flow distortion at such off-design conditions. By blowing pressurized air into the intake near the separation point, the boundary layer is energized and separation can be controlled. This study investigates the applicability of lip blowing, an active flow control technique, to control intake separation and flow distortion at the fan-face. First, intake separation was triggered in a 3D CFD model based on the NASA Common Research Model (CRM) using high AoA cases at cruise condition (Mach number 0.85, Mass flow capture ratio ∼0.7) and the features of separated flow were analyzed. Thereafter, active flow control was introduce to the intake in the form of two types of lip blowing, direct and pitched blowing. The efficacy of lip blowing at achieving separation control in an ultra high bypass ratio turbofan engine intake has been established through this study. The present paper also examines the significance of blowing parameters like the type of blowing, blowing pressure ratio, and blowing slot dimension, at different angles of attack to identify the critical control parameters. Our research successfully establishes proof of concept by demonstrating the feasibility of using lip blowing for separation control in aero-intakes, via numerical modelling. Furthermore, this study also provides crucial insights regarding the important variables to be considered for future experimental studies, and also for detailed studies covering a wider range of operating and blowing conditions.

On the effects of a separation bubble on fan noise

A scale model of a fan stage operating at approach condition is investigated using wall-resolved Large Eddy Simulations. The configuration is a state-of-the-art fan stage (rotor + stator) of an Ultra High Bypass Ratio turbofan engine, and the computational cost has been reduced by simulating a radial slice of a periodic sector. At low fan speeds and Reynolds number, a recirculation bubble can be observed on the suction side of the fan blades, near the leading edge. This recirculation bubble causes the boundary layer transition to turbulence and is associated with high levels of wall pressure fluctuations. The noise spectra upstream of the fan blades show high frequency tones, which are related to the noise generation mechanism of the recirculation bubble. It has been found that the size, position and pressure disturbances in the bubble depend on the mass flow rate. Furthermore, the frequencies and amplitudes of the high frequency tones in the noise spectra also depend on the mass flow rate. As the mass flow rate decreases, the size of the bubble increases, the bubble shifts towards downstream locations, and high levels of wall pressure fluctuations can be found along the suction side of the fan blade. The acoustic signature of the bubble shifts towards lower frequencies with the mass flow rate, but its amplitude increases. A coherence analysis and a Dynamic Mode Tracking technique are used to confirm that high frequency tones can be generated by the recirculation bubble in the separation region. The flow features at these frequencies suggest that a vortex shedding mechanism is related to the noise radiated from the recirculation bubble.

Impact of three-dimensional turbulence modelling on rotor/stator interaction broadband noise

An accurate prediction of Fan/Outlet-Guide-Vane (OGV) interaction broadband noise (BBN) is fundamental to correctly characterise the noise footprint of high bypass ratio turbofan engines. A three-dimensional synthetic turbulence BBN prediction methodology, which accounts for cascade effects and the airfoil geometry using a frequency-domain Linearised Navier–Stokes Solver, is presented in this work. The methodology computes the BBN generated by an infinite three-dimensional (3D) linear cascade using a spectral representation in the spanwise direction. The 3D problem is reconstructed analytically using two-dimensional (2D) simulations, including additional source terms coming from the spanwise spatial derivatives, leading to a high computational efficiency compared to a standard 3D approach. The methodology has been applied to assess the impact of oblique gusts on a Fan/OGV and a low-pressure turbine airfoil, and the results are compared to a 2D methodology and a previously proposed quasi-3D (q3D) formulation. Differences of more than 10 dB arise when comparing the 3D results with a purely 2D approach caused by the over-estimation of the turbulent kinetic energy that can produce cut-on acoustic modes. The validity of a q3D correction to mitigate this 2D effect has been assessed, demonstrating differences smaller than 2 dB concerning the 3D formulation, and therefore, its use can be justified for rapid predictions. The 3D methodology removes the unphysical impact of the 2D cascade resonances that appear in the q3D approach. The differences between the 3D and q3D approaches have been assessed in detail using an azimuthal noise decomposition. Even though the acoustic response can be remarkably affected by changes in the spanwise wavenumber, the noise azimuthal decomposition and frequency spectra exhibit a similar shape because the acoustic response is relatively constant within a significant fraction of the spanwise wavenumbers that enable sound radiation.

Influence Factors for Impact Actions and Transient Trajectories of Fan Blades after Fan Blade Out in Typical 2-Shaft High Bypass Ratio Turbofan Engine

Influence Factors for Impact Actions and Transient Trajectories of Fan Blades after Fan Blade Out in Typical 2-Shaft High Bypass Ratio Turbofan Engine

Empirical estimation of engine-integration noise for high bypass ra-tio turbofan engines

To investigate the impact of installation on jet noise from modern high-bypass-ratio turbofan engines, a model-scale noise experiment with a jet propulsion system and a fuselage model in scale was conducted in the anechoic wind tunnel of ONERA, CEPRA 19. Two area ratios (an area of the secondary nozzle over an area of the primary nozzle), 5 and 7, and various airframe configurations such as wing positions relative to the tip of the engine nacelle and flap angles, were considered. Based on the analysis of experimental data, an empirical model for the prediction of engine installation noise was proposed. The model comprises two components: one is the interaction be-tween the jet and the pressure side of the wing, and the other is the interaction between the jet and the flap tip. The interaction between the jet and the pressure side of the wing contributes to the noise at the low frequencies (≤ 1.5 kHz), and the interaction between the jet and the flap tip con-tributes to the noise at the high frequencies. The proposed model showed a good agreement with the experimental data.

An acoustic liner design methodology based on a statistical source model

The attenuation of fan tones remains an important aspect of fan noise reduction for high bypass ratio turbofan engines. However, as fan design considerations have evolved, the simultaneous reduction of broadband fan noise levels has gained interest. Advanced manufacturing techniques have also opened new possibilities for the practical implementation of broadband liner concepts. To effectively address these elements, practical acoustic liner design methodologies must provide the capability to efficiently predict the acoustic benefits of novel liner configurations. This paper describes such a methodology to design and evaluate multiple candidate liner configurations using realistic, three dimensional geometries for which minimal source information is available. The development of the design methodology has been guided by a series of studies culminating in the design and flight test of a low drag, broadband inlet liner. The excellent component and system noise benefits obtained in this test demonstrate the effectiveness of the broadband liner design process. They also illustrate the value of the approach in concurrently evaluating multiple liner designs and their application to various locations within the aircraft engine nacelle. Thus, the design methodology may be utilized with increased confidence to investigate novel liner configurations in future design studies.

Prediction of fan acoustic blockage on fan/outlet guide vane broadband interaction noise using frequency domain linearised Navier–Stokes solvers

Fan/Outlet-Guide-Vane (OGV) interaction is a major broadband noise source in high bypass ratio turbofan engines. This paper assesses the acoustic shielding created by the fan rotor on the broadband noise generated by the interaction between the fan and the OGV. With this objective in mind, an efficient methodology to account for broadband noise transmission through a fan rotor using two-dimensional linearised frequency domain Navier–Stokes solvers is presented. The radial variations of the flow are retained using a strip-wise approach, which is key to estimate the fan blockage accurately. The methodology has been applied to the AneCom Aerotest (ACAT1) fan rig that is representative of a modern fan, at the three noise certification points and compared with acoustic measurements, namely, frequency spectra and azimuthal mode decompositions. Overall, good agreement on the impact of the rotor shielding on the upstream noise spectra has been achieved. Rotor shielding produces a decrease in the upstream emitted noise of about 2.5, 7 and 9 dB at Approach, Cutback and Sideline conditions, respectively. Thus, its modelling is of paramount importance for an accurate prediction of the engine’s noise footprint. The predicted sound pressure azimuthal decompositions show an excellent qualitative agreement with the experimental data, demonstrating the suitability of the methodology to predict this phenomenon. It is concluded that fan blockage cannot be predicted with conventional semi-analytical techniques based on flat plate approximations. The supersonic pockets and shock-waves present in the fan play a principal role in the upstream acoustic emission at high-speed operating points, which cannot be retained in flat plate-like methodologies. The simulations show that at Sideline, the broadband noise emitted by the engine core can become dominant, which was not anticipated. This conclusion is indirectly supported by measurements.

Transient Analysis and Safety Assessment of Turbofan Engine Structures during Bird Ingestion

The high bypass ratio turbofan engine’s load-carrying structure transient response during bird ingestion was analyzed in accordance with the engine bird ingestion certification regulations, the principles of structural safety assessment were represented, and the structural safety analysis and assessment method of Turbo-Fan engine during bird ingestion were proposed. A high bypass ratio turbofan engine’s FEM was established and verified the rationality when its’ operation. Large bird ingestion into an engine’s procedure was conducted, the dynamic responses of key components on engine’s load-carrying structures during the bird ingestion were discussed, and the safety assessment consequence was obtained. We draw a conclusion that the relevant analysis/simulation data could be submitted to engine certification administration as key documents, the structural safety analysis and assessment method of turbofan engine due to bird ingestion could be applied as analysis and prediction work in the engine bird ingestion certification.

Aerodynamics of intakes of high bypass ratio (hbpr) turbofan engines

Aerodynamics of intakes of high bypass ratio (hbpr) turbofan engines

Aerodynamics of intakes of high bypass ratio (hbpr) turbofan engines

Aerodynamics of intakes of high bypass ratio (hbpr) turbofan engines

Applications of structural efficiency assessment method on structural-mechanical characteristics integrated design in aero-engines

In the design process of advanced aero-engines, it is necessary to carry out an effective analysis method between structural features and mechanical characteristics for a better structural optimization. Based on the structural composition and functions of aero-engines, the concept and contents of structural efficiency can reflect the relation between structural features and mechanical characteristics. In order to achieve the integrated design of structural and mechanical characteristics, one quantitative analysis method called Structural Efficiency Assessment Method (SEAM) was put forward. The structural efficiency coefficient was obtained by synthesizing the parameters to quantitatively evaluate the aero-engine structure design level. Parameterization method to evaluate structural design quality was realized. After analyzing the structural features of an actual dual-rotor system in typical high bypass ratio turbofan engines, the mechanical characteristics and structural efficiency coefficient were calculated. Structural efficiency coefficient of high-pressure rotor (0.43) is higher than that of low-pressure rotor (0.29), which directly shows the performance of the former is better, there is room for improvement in structural design of the low-pressure rotor. Thus the direction of structural optimization was pointed out. The applications of SEAM shows that the method is operational and effective in the evaluation and improvement of structural design.

Prediction of Crosswind Separation Velocity for Fan and Nacelle Systems Using Body Force Models: Part 1: Fan Body Force Model Generation without Detailed Stage Geometry

Modern aircraft engines must accommodate inflow distortions entering the engines as a consequence of modifying the size, shape, and placement of the engines and/or nacelle to increase propulsive efficiency and reduce aircraft weight and drag. It is important to be able to predict the interactions between the external flow and the fan early in the design process. This is challenging due to computational cost and limited access to detailed fan/engine geometry. In this, the first part of a two part paper, we present a design process that produces a fan gas path and body force model with performance representative of modern high bypass ratio turbofan engines. The target users are those with limited experience in turbomachinery design or limited access to fan geometry. We employ quasi-1D analysis and a series of simplifying assumptions to produce a gas path and the body force model inputs. Using a body force model of the fan enables steady computational fluid dynamics simulations to capture fan–distortion interaction. The approach is verified for the NASA Stage 67 transonic fan. An example of the design process is also included; the model generated is shown to meet the desired fan stagnation pressure ratio and thrust to within 1%.

Numerical analysis of hub cavity leakage

Purpose This paper aims to predict the effect of the hub cavity leakage on the overall performance with numerical simulations in the fan/booster of a high bypass ratio turbofan engine. Design/methodology/approach Simulations are conducted for leakage at the fan, the outlet of guide vane and the three-stage booster, as well as hub leakage (contain cavities and sealing). The results obtained are compared to the corresponding simulations without hub leakage. Findings The rotor/stator interaction locations are evaluated to discover a better location. The results show that the seal tooth structure produces secondary flow and turbulence in the root of blade suction surface, which increases the aerodynamic loss. The sealing clearance should be controlled to shrink the turbulent region and decrease the leakage. Practical implications This work can provide a theoretical guidance and technical support for the compressor design, which avoid many repeated manufactures and reduce waste of resources. Originality/value This work improves the understanding of the impact mechanism of hub cavity leakage on the performance when the clearance size of seal is variable.

The Nonlinear Single Controller of DGEN380 Aero Engine Design

The advanced nonlinear sliding mode control method of DGEN380 aero engine is presented in this paper. This aero engine is a small high bypass ratio turbofan engine by which the nonlinear control approach of the aero engine is invested. And this paper focuses on the power management function of the aero engine control system which includes steady control and transient control. The mathematical model of DGEN380 aero engine is built by a set of nonlinear dynamic equation that is validated by experimental data. The single controller based on sliding mode approach is designed that can keep some certain thrust levels during steady state and maintain repeatable performance during transient operation from one requested thrust level to another. The single controller can offset the impact of the signal noise and harmonic disturbance at a certain power point. And the dynamic performance of the single controller is satisfactory at the transient process. The experiment is conducted by aero engine test bench for the single control.

Investigation of Vibration Characteristics of Titanium Wide-Chord Fan Blade

The vibration characteristics of a wide-chord fan blade affect the safety, reliability, and operability of high-bypass ratio turbofan engines. In this study, the vibration characteristics of a fan blade were investigated using numerical and experimental methods. First, the natural frequencies and mode shapes were obtained and verified. Then, the rotating speed and frequency margins were employed to analyze the stability of the blade. The critical crossings in the Campbell diagram were indicated and evaluated. Next, the strain energy density index and weaklink were used to evaluate the dangerous locations for the high-cycle fatigue characteristics of the blade. Finally, single- and multi-axis random-excitation tests were performed. Results indicated that low-order bending modes were dominant under circumferential- and axial-direction excitations, while the torsional mode response was higher under radial-direction excitation. The weaklinks for different excitation directions exhibited different characteristics. This work presents a comprehensive understanding of the fan-blade vibration and response characteristics.

A mixed-fidelity computational model of aero engine for inlet distortion

This paper presents a mixed-fidelity model to investigate the effect of complex inlet distortion on aero gas turbine engines. The approach is developed by integrating a three-dimensional body force model of multistage compressors and a classical two-dimensional parallel engine model. The internal flow field of a high bypass ratio turbofan engine under different forms of total pressure distortion is simulated by the model. The simulations are discussed in depth to reveal the features of the distorted flow field in the compression components under the whole engine environment. The relationship between the overall performance of the engine and the intensity of inlet total pressure distortion is investigated quantitatively. It is evident that the mixed-fidelity model has the capability to quantitatively evaluate the effect of complex inlet distortion on the performance and the internal flow field of engines with low computational costs.