Search Results (14)

High-performance geared turbofan engines generate significant heat within the planetary power gearbox. This study presents the thermal design of an integrated fan guide vane heat exchanger aimed at recovering gearbox heat losses with minimal pressure loss and converting them into useful propulsive energy via the Junkers–Meredith Effect. Hot gearbox oil is routed through hollow fan static guide vanes, enabling heat transfer to the bypass airflow while simultaneously reducing oil temperature and augmenting thrust. A comprehensive analytical framework is applied, incorporating heat transfer modeling, guide vane geometry reconstruction, lubrication flow sizing, and propulsion performance evaluation for both take-off and cruise flight conditions, using the PW1127G-JM geared turbofan as the reference engine. The results indicate that the proposed system can achieve a thrust increase of up to 6.4% at the end of take-off and deliver a thrust-specific fuel consumption reduction of up to 5.6% during take-off and approximately 2% during cruise. While sufficient heat dissipation is achieved under cruise conditions, take-off operation requires a higher transient oil temperature. Overall, this study demonstrates that integrating heat recovery into existing engine structures offers a promising pathway to enhance propulsion efficiency, reduce fuel consumption, and support more sustainable aircraft engine designs. Full article

High-speed, low-pressure turbines in geared turbofans operate at transonic exit Mach numbers and low Reynolds numbers. Engine-relevant data remain scarce. The SPLEEN C1 linear cascade was investigated at $M_{\mathrm{out}}=0.70–0.95$ and $R{e}_{\mathrm{out}}=\mathrm{65,000}–\mathrm{120,000}$ under steady inlet flow. Experiments were combined with 2D RANS and MISES, including transition modeling and inlet-turbulence decay calibrated to measurements. Results are consistent with conventional LPT behavior: loss decreased with increasing Mach and Reynolds numbers, except when shocks interacted with the blade boundary layer ($M\approx 0.95$). Profile loss dropped by $23\%$ from $M=0.70$ to $0.95$ at $Re=\mathrm{70,000}$, as well as by $19\%$ at $M=0.80$ when open separation is suppressed. Secondary loss decreased by up to $25\%$ at $Re=\mathrm{70,000}$ and showed weak sensitivity to the Reynolds number. A coupled loss model predicted profile loss with a root-mean square error of 4.7%. Secondary-loss modeling reproduced global trends: separating endwall dissipation from mixing kept errors within $\pm 10\%$ for most cases, but accuracy degraded near the shock–boundary layer interaction case and at the highest Reynolds number. Mixing dominated endwall loss (∼75%), with the passage vortex contributing ∼50% (±10%) of the mixing component. Full article

Surface Air-Cooled Oil Coolers (SACOCs) can become a critical component in managing the increasing thermal loads of modern turbofan engines. Installed within the bypass duct, SACOCs utilize high-mass flow bypass air for convective heat rejection, reducing reliance on traditional Fuel-Oil Heat Exchangers. This review explores SACOC design principles, integration challenges, aerodynamic impacts, and performance trade-offs. Emphasis is placed on the balance between thermal efficiency and aerodynamic penalties such as pressure drop and flow distortion. Experimental techniques, including wind tunnel testing, are discussed alongside numerical methods, and Conjugate Heat Transfer modeling. Presented studies mostly demonstrate the impact of fin geometry and placement on both heat transfer and drag. Optimization strategies and Additive Manufacturing techniques are also covered. SACOCs are positioned to play a central role in future propulsion systems, especially in ultra-high bypass ratio and hybrid-electric architectures, where traditional cooling strategies are insufficient. This review highlights current advancements, identifies limitations, and outlines research directions to enhance SACOC efficiency in aerospace applications. Full article

This study investigates the time-resolved aerodynamics in the cavity regions of a full-scale, high-speed, low-pressure turbine stage representative of geared turbofan engines. The turbine stage is tested in the von Karman Institute’s short-duration rotating facility at different purge rates (PR) injected through the upstream hub cavity. Spectra from the shroud and downstream hub cavity show perturbations linked to blade passing frequency and rotor speed. Asynchronous flow structures associated with ingress/egress mechanisms are observed in the rim seal of the purged cavity. At 0% PR, the ingress region extends to the entire rim seal, and pressure fluctuations are maximized. At 1% PR, the instability is suppressed and the cavity is sealed. At 0.5%, the rim-seal instability exhibits multiple peaks in the spectra, each corresponding to a state of the instability. Kelvin–Helmholtz instabilities are identified as trigger mechanisms. A novel technique based on the properties of the cross-power spectral density is developed to determine the speed and wavelength of the rotating structures, achieving higher precision than the commonly used cross-correlation method. Moreover, unlike the standard methodology, this approach allows researchers to calculate the structure characteristics for all the instability states. Spectral analysis at the turbine outlet shows that rim-seal-induced instabilities propagate into regions occupied by secondary flows. A methodology is proposed to quantify the magnitude of the induced fluctuations, showing that the interaction with secondary flows amplifies the instability at the stage outlet. Full article

Aviation accounts for a significant share of global CO₂ emissions, necessitating efficient propulsion technologies to achieve net-zero emissions by 2050. Geared turbofan architectures offer a promising solution by enabling higher bypass ratios and improved fuel efficiency. However, geared turbofans introduce significant aerodynamic and structural challenges, particularly in the low-pressure turbine. Current understanding of high-speed low-pressure turbine behavior under engine-representative conditions is limited, especially regarding unsteady wake interactions, secondary flows, and compressibility effects. To address these gaps, this work presents a novel test case of high-speed low-pressure turbines, the SPLEEN C1. The test case and experimental methodology are depicted. The study includes the commissioning and characterization of a transonic low-density linear cascade capable of testing quasi-3D flows. The rig’s operational stability, periodicity, and inlet flow characterization are assessed in terms of loss and turbulence quantities to ensure an accurate representation of engine conditions. These findings provide a validated experimental platform for studying complex flow interactions in high-speed low-pressure turbines, supporting future turbine design and efficiency advancements. Full article

As aviation demand rises, fossil jet fuel consumption follows, thus increasing focus on sustainable aviation fuels to reduce aircraft greenhouse gas emissions. While advanced technologies and optimized operations play a role, alternative fuels, especially non-drop-in options like Liquefied Natural Gas (LNG) and methanol, offer promising potential for significant emission reductions if used in current aero-engines. LNG, a candidate near-term replacement of fossil jet fuel and methanol, even though a less conventional option in aviation, present advantages. Both fuels showcase the ability to generate the same thrust output by also achieving lower post-combustion temperatures, thereby enhancing component life and reducing emissions. Inversely, requesting equal post-combustion temperature as the baseline kerosene operation of the engine can produce greater thrust output, a much needed result for such fuels with low volumetric energy density, which causes greater take-off thrust demand mainly due to their larger tank requirements. This study uses advanced 0-D engine models coupled with detailed chemistry 1-D burner models and mission analysis tools to assess the aforementioned trends of LNG and methanol used to power a current geared turbofan engine. The aim of this work is to provide insights into the advantages, the limitations and the overall viability of the fuels in question as less polluting aviation fuels, addressing both environmental impact and operational feasibility in future aviation applications. According to findings of this article, when compared with Jet-A, LNG can reduce post-combustion temperature by an average of 1% or increase net-thrust by 3% while lowering $C{O}_2$, $N{O}_x$ and $CO$ emissions by 20%, 46% and 39%, respectively. Adversely, methanol is capable of lessening post-combustion temperature by 3% or enhancing thrust output by 10% while also reducing $C{O}_2$, $N{O}_x$ and $CO$ emissions by an average of 6%, 60% and 38%, respectively. Full article

Runway Safety Assistant Foreseeing Excursions (RUNSAFE) is a complete embedded system solution, that predicts a potential runway overrun of a civil aviation aircraft during takeoff and landing. This work examines the feasibility of such a system, through the algorithms and computations that predict the overruns. The system executes both static and dynamic calculations, with the former being dependent on and the latter independent to the user’s inputs. Their outcomes and the runway’s length are compared in real time to assess if the process will end up in an overrun. All inputs are specifically selected to either be available to the pilots or be retrieved from the existing avionics systems of the cockpit. A performance evaluation is conducted on both static and dynamic calculations, and metrics unveil the accuracy of the predictions and the time needed to converge to a reliable result. The solution is adapted for a Boeing 737-800 aircraft with CFM56-7B engines, but the calculations also apply for similar aircraft equipped with tricycle landing gear and turbofan engines, namely the whole Boeing 737 family, the Airbus A320 family, etc. The system is aligned with current standards and certification specifications, where applicable. Full article

This paper presents a modular, flexible, extendable and fast-computational framework that implements a multidisciplinary, varying fidelity, multi-system approach for the conceptual and preliminary design of novel aero-engines. In its current status, the framework includes modules for multi-point steady-state engine design, aerodynamic design, engine geometry and weight, aircraft mission analysis, Nitrogen Oxide (NOx) emissions, control system design and integrated controller-engine transient-performance analysis. All the modules have been developed in the same software environment, ensuring consistent and transparent modeling while facilitating code maintainability, extendibility and integration at modeling and simulation levels. Any simulation workflow can be defined by appropriately combining the relevant modules. Different types of analysis can be specified such as sensitivity, design of experiment and optimization. Any combination of engine parameters can be selected as design variables, and multi-disciplinary requirements and constraints at different operating points in the flight envelope can be specified. The framework implementation is exemplified through the optimization of an ultra-high bypass ratio geared turbofan engine with a variable area fan nozzle, for which specific aircraft requirements and technology limits apply. Although the optimum design resulted in double-digit fuel-burn benefits compared to current technology engines, it did not meet engine-response requirements, highlighting the need to include transient-performance assessments as early as possible in the preliminary engine design phase. Full article

This paper investigates the impact of thermal management methods on the design point and synthesis exchange rates of an ultra-high bypass ratio geared turbofan engine. In a typical thermal management system, where heat is managed by means of heat exchangers that transfer engine waste heat into oil, air, or fuel. However, the utilization of air–oil and fuel–oil heat exchangers has an adverse impact on engine performance. This paper investigates the impact on and engine’s specific fuel consumption and summarizes it into common exchange rates for different thermal management configurations. The results show that any pressure loss in the bypass duct results in a severe specific fuel consumption penalty (an increase of 1% pressure loss in the bypass duct causes a 2% specific fuel consumption increase at cruise conditions). In addition, quite severe is the impact of extracting air from the gas path, particularly when the bleed location is in the bypass duct or the high-pressure compressor. It is also found that the utilization of a fuel–oil heat exchanger improves the specific fuel consumption at a higher rate than an air–oil heat exchanger. For the performance characteristics of the examined engine, the specific fuel consumption benefit with the former is 1.33%, while for the latter it is 0.38%. Full article

The mesh stiffness of gear pairs used in aerospace applications, such as geared turbofan, has a vital influence on vibration and noise. To compensate for the deficiencies of the conventional method that does not consider slice coupling and structure coupling simultaneously, a comprehensive mathematical model for computing the mesh stiffness of helical gears is established. In this novel model, the effect of structure coupling and slice coupling between neighboring sliced gears are considered. The effect of the axial component of meshing force is also taken into account simultaneously. The results obtained by the comprehensive model are consistent with the finite element method and it proves that the novel mathematical model is sound. The influences of the helical angle and addendum modification coefficient on mesh stiffness are studied. The results show that the mesh stiffness of helical gears would be decreased in multiteeth regions caused by structure coupling. With or without consideration of the axial component, the relative mean values of mesh stiffness become larger with an increasing helical angle. The fluctuation value of mesh stiffness decreases when a positive addendum modification coefficient is adopted. The addendum modification also changes the phase of mesh stiffness. This study is helpful for a vibration analysis of gear transmission systems. Full article

In this work, effective methods for monitoring friction and wear of journal bearings integrated in future UltraFan^® jet engines containing a gearbox are presented. These methods are based on machine learning algorithms applied to Acoustic Emission (AE) signals. The three friction states: dry (boundary), mixed, and fluid friction of journal bearings are classified by pre-processing the AE signals with windowing and high-pass filtering, extracting separation effective features from time, frequency, and time-frequency domain using continuous wavelet transform (CWT) and a Support Vector Machine (SVM) as the classifier. Furthermore, it is shown that journal bearing friction classification is not only possible under variable rotational speed and load, but also under different oil viscosities generated by varying oil inlet temperatures. A method used to identify the location of occurring mixed friction events over the journal bearing circumference is shown in this paper. The time-based AE signal is fused with the phase shift information of an incremental encoder to achieve an AE signal based on the angle domain. The possibility of monitoring the run-in wear of journal bearings is investigated by using the extracted separation effective AE features. Validation was done by tactile roughness measurements of the surface. There is an obvious AE feature change visible with increasing run-in wear. Furthermore, these investigations show also the opportunity to determine the friction intensity. Long-term wear investigations were done by carrying out long-term wear tests under constant rotational speeds, loads, and oil inlet temperatures. Roughness and roundness measurements were done in order to calculate the wear volume for validation. The integrated AE Root Mean Square (RMS) shows a good correlation with the journal bearing wear volume. Full article

In this paper, a turbo-electric propulsion system was analyzed, and its performance was assessed. The aircraft considered here was a single-aisle, medium-range configuration targeting a capacity of 150 Pax. The propulsion concept comprised two boosted geared turbofan engines mounted under-wing. Those main engines were supported by an electrically driven aft-propulsor contributing to the thrust generation and by taking advantage of ingesting the boundary layer of the fuselage for potentially higher levels of propulsive efficiency and allowing for the improved operation of the main engines. The performance assessment as carried out in the context of this paper involved different levels: Firstly, based on the reference aircraft and the detailed description of its major components, the engine performance model for both main engines, as well as for the electrically driven aft-propulsor was set up. The methodology, as introduced, has already been applied in the context of hybrid-electric propulsion and allowed for the aforementioned aircraft sizing, as well as the subsequent gas turbine multi-point synthesis (simulation). A geared turbofan architecture with 2035 technology assumptions was considered for the main engine configuration. The present trade study focused on the design and performance analysis of the aft-propulsor and how it affected the performance of the main engines, due to the electric power generation. In order to allow for a more accurate description of the performance of this particular module, the enhanced streamline curvature method with an underlying and pre-optimized profile database was used to design a propulsor tailored to meet the requirements of the aft propulsor as derived from the cycle synthesis and overall aircraft specification; existing design expertise for novel and highly integrated propulsors could be taken advantage of herein. The resulting performance characteristics from the streamline curvature method were then fed back to the engine performance model in a closely coupled approach in order to have a more accurate description of the module behavior. This direct coupling allowed for enhanced sensitivity studies, monitoring different top-level parameters, such as the thrust/power split between the main engines and the aft propulsor. As a result, different propulsor specifications and fan designs with optimal performance characteristics were achieved, which in return affected the performance of all subsystems considered. Full article

In some cases, the improvement of the bypass ratio (BPR) of turbofans is pursued for military or civilian purposes owing to economic, environmental, and performance reasons, among others. However, high-BPR turbofans suffer from incompatibility of spool speed, complex structure for manufacture, development difficulty, and substantially increasing costs, especially for those with small batch production. To deal with the issues, a novel low-cost concept of high-BPR turbofan with air-driven fan (ADTF) is presented in this research. First, the problems faced by high-BPR turbofans are discussed, and the difficulties of geared turbofan (GTF), which is developed as a solution to the problems, are analyzed. A novel turbofan with potential advantages is proposed, and its basic theory is interpreted. Second, high-BPR ADTF is analyzed at the top level, and the design principle and important primary parameters are discussed. Some important concepts and criteria are proposed, enabling the comparison between ADTF and GTF. Finally, an air-driven fan system, the core part of ADTF, is exploratorily designed, and numerical simulation is performed to demonstrate its feasibility. Full article

By 2050, the evolutionary approach to aero engine research may no longer provide meaningful returns on investment, whereas more radical approaches to improving thermal efficiency and reducing emissions might still prove cost effective. One such radical concept is the addition of a secondary power cycle that utilizes the otherwise largely wasted residual heat in the core engine’s exhaust gases. This could provide additional shaft power. Supercritical carbon dioxide closed-circuit power cycles are currently being investigated primarily for stationary power applications, but their high power density and efficiency, even for modest peak cycle temperatures, makes them credible bottoming cycle options for aero engine applications. Through individual geometric design and performance studies for each of the bottoming cycle’s major components, it was determined that a simple combined cycle aero engine could offer a 1.9% mission fuel burn benefit over a state-of-the-art geared turbofan for the year 2050. However, the even greater potential of more complex systems demands further investigation. For example, adding inter-turbine reheat (ITR) to the combined cycle is predicted to significantly improve the fuel burn benefit. Full article