Jet Engine Research Articles

The Effect of Unsteady Inlet Boundary Conditions on the Aero-Thermal Behavior of High-Pressure Turbine Vanes – A Numerical Study Using Scale-Resolving Simulations

Abstract This paper presents the application of a novel method to prescribe unsteady boundary conditions to transient, scale-resolving computational fluid dynamics simulations of the high-pressure turbine in modern jet engines. The methodology is based on the compression of the interface data at the combustor–turbine interface, using proper orthogonal decomposition and Fourier series (PODFS). Doing so can reduce the stored data at the interface drastically. The capability of the PODFS method to produce realistic inlet boundary conditions was demonstrated in previous work. Here, the method is applied to a turbine case. The outlet data of a combustor simulation is used to create the PODFS boundary conditions for a scale-resolving simulation of a simplified first nozzle guide vane of the high-pressure turbine. This simulation is compared with simulations with steady-state boundary conditions to show the effect of unsteadiness in the inlet boundary condition on the aerodynamic and thermal behaviors of the turbine. While the aerodynamics show minor sensitivity against the way of applying the inlet boundary conditions, the thermal behavior of the vanes is strongly affected by the modeling of combustor unsteadiness.

Enhancing thermal stability and corrosion resistance of carbon-carbon composites with iridium coatings deposited by electron beam physical vapor deposition

Abstract Carbon–carbon (C−C) composites are extensively used in high-temperature environments such as Combustor Liners and Turbine Blades in jet engines and Throat Inserts, Nozzle Extensions and Exit Cones in rocket engines due to their excellent thermal stability and mechanical properties. However, at temperatures exceeding 800 °C, these composites require additional protection to prevent degradation. This study aims to investigate the behavior of C−C composites when coated with high-purity metallic iridium using Electron Beam Physical Vapor Deposition (EBPVD). The research problem focuses on enhancing the high-temperature performance and corrosion resistance of C−C composites for aerospace applications. The methodology involves depositing a uniform 5.6 microns thick iridium coating on C−C substrates and characterizing the coating’s microstructure, hardness, and corrosion resistance. FESEM micrographs reveal that the iridium coating adheres uniformly to the substrate without any seepage, and XRD analysis confirms an FCC crystal structure with a densely packed grainy surface. Corrosion tests were conducted using a BIOLOGIC electrochemical workstation in a sodium chloride environment indicate a corrosion rate of 0.00307 mm year−1. The Nyquist, Bodo plots, and Taffel plots were constructed for the better understanding of the corrosion mechanism. While the OCP was constructed to understand the stability and the corrosion resistance of the C−C samples. Microhardness of the coating, measured under a normal applied load of 0.20 N, is 702 HV. The coated samples also could withstand thermal shocks between −40 °C and 1500 °C for 40 h without observable damage or color change. These findings demonstrate the potential of iridium-coated C−C composites to maintain structural integrity and performance in extreme aerospace environments, significantly impacting the field by providing a reliable protective solution for high-temperature applications.

Brayton Cycle Analysis of the Effect of Wake Ingestion on Aircraft Range

The effect of wake ingestion on the propulsive efficiency of turbojet and turbofan engines has been examined to determine the effect of wake ingestion on jet aircraft range. In a new approach, the Brayton turbine cycle was analyzed to show how wake ingestion affects the thrust and specific fuel consumption of jet engines. It is argued that it is not necessary to add an expression for propulsive efficiency to the Breguet range equation, because the thrust-specific fuel consumption is an explicit function of the inlet Mach number. It is concluded that wake ingestion does not increase the aircraft’s maximum range because it reduces the engine’s maximum thrust.

Effect of the Addition of Cu and Al on the Microstructure, Phase Composition and Properties of a Ti-6Al-4V Alloy Obtained by Selective Laser Melting

The present study considers the samples of an Ti-6Al-4V alloy obtained by selective laser melting with the addition of a 10% Cu-Al powder mixture. The microstructure, elemental composition and phase composition, as well as the physico-chemical properties, have been investigated by the methods of electron microscopy, X-ray phase analysis, and bending testing. The obtained samples have a relative density of 98.5 ± 0.1%. The addition of the Cu-Al powder mixture facilitates supercooling during crystallization and solidification, which allows decreasing the size and changing the shape of the initial β-Ti grains. The constant cooling rate of the alloy typical for the SLM technology has been shown to be able to prevent martensitic transformation. The formation of a structure that consists of β-Ti grains, a dispersed eutectoid mixture of α-Ti and Ti2Cu grains, and a solid solution of Al in Cu has been revealed. In the case of doping by the 10% Cu-Al mixture, the physico-mechanical properties are improved. The hardness of the samples amounts to 390 HRC, with the bending strength being 1550 ± 20 MPa and deformation of 3.5 ± 0.2%. The developed alloy can be recommended for applications in the production of parts of jet and car engines, implants for medicine, and corrosion-resistant parts for the chemical industry.

Investigation of the cooling hole blockage induced by different thermal spray TBC deposition processes

High-temperature turbine airfoils and combustion chamber walls in jet engines require sufficient cooling via cooling holes and thermal barrier coating systems (TBCs) to protect them from hot combustion gases. As the demand for greater efficiency and higher firing temperatures in jet engines increases, there is a corresponding need for more advanced film cooling methods, such as the use of more complex hole geometries. The use of Additive Layer Manufacturing (ALM) techniques allows the production of such intricate cooling holes, enhancing the flow of cooling air onto component surfaces. Conventional TBC deposition techniques, for example Atmospheric Plasma Spraying (APS) or Electron Beam Physical Vapor Deposition (EB-PVD), often lead to partial or complete blockage of cooling holes. This study compares the blockage of TBCs deposited on conventionally-sheet alloys with standard cooling holes and ALM alloys with more complex cooling holes using APS as a baseline process. Additionally, alternative plasma spray deposition technologies such as Suspension Plasma Spraying (SPS) and Plasma Spray-Physical Vapor Deposition (PS-PVD) were explored. The aim was to determine the effectiveness of these processes in preventing blockage compared to the traditional APS process. The experimental results showed that the formation of the coating, whether originating from splats or from the vapor phase, the feedstock particle size, and the cooling hole geometry can all affect the blockage. It was demonstrated that PS-PVD, with its vapor-induced deposition, is highly effective in minimizing blockage, regardless of the cooling hole geometry.

Validation of methods for increasing the efficiency of detonation jet engines

Validation of methods for increasing the efficiency of detonation jet engines

Hydrodynamic performance evaluation of pump-jet propulsion based on the toroidal propeller

Pump jet propulsion (PJP) is a widely used propulsion method for underwater vehicles. Compared with traditional propeller propulsions, it has the characteristics of higher propulsion efficiency, lower noise, and better performance. A novel propeller with annular blades, named as ‘the toroidal propeller’, is designed and discussed with its characteristic parameters. Then the novel propeller is installed to the PJP and Suboff submarine to evaluate its performance with Computational Fluid Dynamics (CFD) simulations. The high-speed range of modified submarine with the toroidal propeller is also predicted and analyzed through propulsion parameters. The results indicate that when the toroidal propeller is applied to the PJP of underwater vehicle, its propulsion efficiency can reach 0.88 at the speed coefficient of 1.2. When the rotator speed is 5000 RPM, the pump jet thruster with toroidal propellers can continue to provide effective thrust, which will easily cause the speed of submarine to exceed 60 kn.

Assessment of a body force modeling approach to examine the aerodynamics of high bypass ratio fan stages

The primary focus of modern civil jet engine intake design is to enhance propulsive efficiency through an increase in the bypass ratio of the turbofan engine, which requires an enlargement in fan diameter. However, this enlargement results in increased weight and drag due to the need for a larger nacelle to surround the fan. To mitigate these issues, efforts are being made to shorten the axial length of the aircraft engine intakes. Nonetheless, this reduction leads to more vulnerable fan aerodynamics since the diffusion within the intake must occur over a shorter distance, causing a higher possibility of flow separation. Common intake design methods employ throughflow nacelle models that do not consider the aerodynamic effects of the fan, including blockage, mass flow redistribution, and suction. The utilization of a full annulus domain numerical setup, which is necessary to capture inlet distortions, demands excessive computational resources particularly during the design phase. As a result, reduced order models, such as the body force model, can be utilized to simulate fan intake aerodynamics. This paper will assess the body force model and its abilities by comparing conventional bladed single passage simulations with the body force approach.

Detrimental Effects of βo-Phase on Practical Properties of TiAl Alloys

The TNM alloy, a βo-phase-containing TiAl alloy, has been withdrawn from use as a last-stage turbine blade in commercial jet engines as it suffered frequent impact fractures in service, raising doubts regarding the necessity of the βo-phase in practical TiAl alloys. Here, we evaluate the practical properties required for jet engine blades for various TiAl alloys and investigate the effects of the βo-phase thereupon. First, we explore the influence of the βo-phase content on the impact resistance and machinability for forged Ti–43.5Al–xCr and cast Ti–46.0Al–xCr alloys; the properties deteriorate significantly at increasing βo-phase contents. Subsequently, two practical TiAl alloys—TNM alloy and TiAl4822—were prepared with and without the βo-phase by varying the heat treatment temperature for the former and the Cr concentration for the latter. In addition to impact resistance and machinability, the creep strength is significantly reduced by the presence of the βo-phase. Overall, these findings suggest that the βo-phase is an undesirable phase in practical TiAl alloys, especially those used for jet engine blades, because, although the disordered β-phase is soft at high temperatures, it changes to significantly more brittle and harder βo-phase after cooling.

Resource reallocation across successive systemic innovations: How Rolls‐Royce shaped the evolution of the turbojet, turboprop, and turbofan

AbstractResearch SummaryDespite the importance of resource reallocation in shaping a variety of strategic outcomes, strategy scholars have paid only limited attention to the processes by which firms reallocate their resources across successive systemic innovations. To explore these processes, we conducted an in‐depth historical case study on Rolls‐Royce's role in three distinct systemic innovations that marked the transition from piston engines to jet engines in the civil aviation industry: the turbojet, the turboprop, and the turbofan. The analysis helps explain how and why Rolls‐Royce's central role stemmed from its ability to reallocate existing non‐scale free organizational and technical resources. A key finding of this study is the identification of the horizontal transfer of functional modules as a critical process, especially during the incipient phase of a systemic innovation. The analysis also highlights the role that specific organizational arrangements, particularly a firm's integrative capabilities, have in shaping the effectiveness with which resources are reallocated.Managerial SummaryFocusing on resource reallocation is important to understand why some firms effectively reallocate their resources through successive systemic innovations while others cannot, even if they have similar resources and face the same environmental conditions. By delving into the technological aspects of aeroengine development and exploring why Rolls‐Royce had the capabilities to successfully integrate key functional modules across various modular levels, we clarify the relationship between technology and organization that underlies resource reallocation—a topic that has received only scant attention in the strategy literature.

Modelling of JP-8 distributed combustion using a HyChem mechanism under gas turbine conditions

The critical advantages of liquid fuels in aviation over alternative energy carriers imply their dominance in the upcoming decades. The Mixture Temperature Controlled (MTC) combustion concept allows spatially homogeneous, efficient burning (distributed combustion) with low pollutant emission. MTC combustion of jet fuel JP-8 was investigated in an atmospheric burner, and the measured pollutant concentrations in the flue gas were reproduced using the Hybrid Chemistry (HyChem) approach employing Perfectly Stirred Reactor simulations. Using this robust approach comes with losing spatiotemporal characteristics if the mixture homogeneity assumption is globally valid. The effect of residence time and pressure under typical gas turbine operating conditions was investigated. Stable combustion was present above 3 ms residence time at pressures up the 60 bar, which was the upper limit of the investigated regime, while the lower residence time limit of stable combustion was 0.3 ms. The residence time interval of stable operation could be extended by applying flue gas recirculation. NO emission can be reduced by increasing the operating pressure, while the N2O production is dominant only up to 20 bar and in the 10–100 ms residence time range. CO emission vanishes above 10 ms residence time. Ultra-low emission operation requires >20 bar pressure and 10 ms residence time with distributed combustion, requiring larger combustion chambers for future jet engines.

Characteristics of Ice Super Saturated Regions in Washington, D.C. Airspace (2019–2023)

Contrails are estimated to contribute 2% of the Earth’s anthropogenic global warming. Contrails are ice crystal clouds formed by the emission of soot and water vapor from jet engines in atmospheric conditions known as Ice Super Saturated (ISS) regions. The formation of contrails can be avoided by flying over or under the ISS regions. Aircraft operators/dispatchers and air traffic control need to know the location of ISS regions in a given airspace to flightplan to avoid contrails. This paper describes the statistics for the presence of ISS regions in the airspace over metropolitan Washington, D.C. These statistics can be used to better understand the operational implications for contrail avoidance. Based on the measurements taken from the twice-daily launch of an aerosonde from Sterling, Virginia (adjacent to Washington, D.C.), analysis of five years of data (2019–2023) indicated that this airspace experiences ISS regions 40% of the days. ISS regions were equally likely during daylight hours (26%) than nighttime (27%). The vertical depth of the ISS region averaged 3000 feet but with a median of 2000 feet. The ISS region floor and ceiling varied by season, with an annual average floor of FL330 and ceiling of FL360. The implications of these results on the operations to avoid contrails, limitations, and future work are discussed.

Off-design analysis of the inverted Brayton cycle engine

PurposeThe purpose of this study is to perform an off-design analysis of the inverted Brayton cycle engine.Design/methodology/approachThe off-design analysis equations of the inverted Brayton cycle engine were first derived in this study and the control parameters of the inverted Brayton cycle engine were first determined and investigated.FindingsIt is observed that by controlling the total temperature decrease in cooling section, it is possible to adapt the engine for low specific fuel consumption working conditions or high thrust working conditions. Specific fuel consumption is reduced by 27.1 % by stopping cooling in the cooling section and thrust is increased by 27.6 % by working with full load of the cooling section (500 K temperature decrease in cooling section). It is observed that thrust depending on the flight Mach number increases with an increase in flight Mach number and reaches a peak value at 5.21 flight Mach number and reduces by 80.8 % at 6 flight Mach number relative to the peak value. The specific fuel consumption increases rapidly as the Mach number increases, and the specific fuel consumption is 49.0 g/[kN.s] at Mach 1, reaches 70.4 g/[kN.s] at Mach 5 and increases to 412 g/[kN.s] at Mach 6. The specific fuel consumption increases from 68.1 to 73.0 g/(kN.s) and the thrust decreases from 16.5 to 13.3 kN as the total preburner exit temperature increases from 1,500 to 2,000 K. Specific fuel consumption decreases from 83.1 to 64.8 g/(kN.s) and thrust increases from 4.60 to 11.08 kN depending on afterburner exit total temperature increase from 1,800 to 2,500 K.Research limitations/implicationsThe cooling section reduces total temperature of the gas flow to lower values to increase the compressor total pressure ratio. The compressor increases the total pressure of the gas flow to the optimum total pressure ratios to increase the nozzle exit Mach number and gain more thrust. The afterburner increases the total temperature of the gas flow to increase the sound speed in the nozzle exit to increase thrust. The nozzle expands the gas flow to reduce the static pressure of the gas flow to near the optimum value, atmosphere pressure, to increase thrust and reduce specific fuel consumption.Practical implicationsHypersonic and supersonic air vehicles can use the current engine model for the its own propulsion systems.Social implicationsAfter first heavier than air flight, aero engines was designed for only used for aero vehicle. Internal combustion engines were used for propelled propeller aircraft at the first term of aircraft. However, propeller-propelled aircrafts are not sufficient to increase aircraft velocity to supersonic Mach numbers due to the shock losses of propeller, so the supersonic era was only introduced by revolution in propulsion systems with new concept. A jet engine was developed to be candidate for supersonic flight.Originality/valueOff-design analysis equations of an inverted Brayton cycle engine were first derived in this study. Furthermore, the control parameters of the inverted Brayton cycle engine were first determined and investigated in this paper.

Investigation of the effect of biofuel addition to jet fuel on engine performance and emissions in model jet engine

The use of biofuel reinforced fossil fuels is increasing day by day, thanks to such as reducing the carcinogenic effects of fossil fuels and reducing the global warming effect. The unmanned aerial vehicle breakthrough made in our country, especially in the defense industry, will ensure that the use of smaller unmanned aerial vehicles becomes more widespread in the future, allowing us to reach more effective and economical solutions. In this study, biofuel was obtained from safflower oil, and the effect of adding various amounts of biofuel to kerosene in a model jet engine on engine performance, and emissions was examined. The closest results to kerosene in fuel consumption, thrust force and the use of biofuel to reinforce fossil fuels is increasing day by day. This is due to its ability to reduce the carcinogenic effects of fossil fuels and also to reduce the global warming effect. In Türkiye, especially in the defense industry, there has been a significant breakthrough in unmanned aerial vehicle technology. This breakthrough will ensure that the use of smaller unmanned aerial vehicles becomes more widespread in the future, allowing us to reach more effective and economical solutions. In this study, biofuel was produced from safflower oil. Researchers examined the effect of adding different amounts of biofuel into kerosene fuel in a model jet engine. Engine performance and emissions were analyzed in the study. When the specific fuel consumption of kerosene fuel is compared to the average of all cycles of other fuels, it is 5.6 % more than B10 fuel, 12.4 % more than B20 fuel and 15 % more than B30 fuel. 8.3 % less thrust force was obtained. The highest turbine inlet temperature values were obtained with Kerosene fuel. Similar results were obtained in terms of emissions, but the best results were obtained with Kerosene fuel. When the averages of the entire experiment with biodiesel blend fuels were compared, it was stated that it constituted an acceptable alternative fuel.

Advanced acoustic simulation of aircraft test environments: integration of the direct field acoustic testing methodology

In aeroacoustic engineering, replicating real-world environments in a controlled setting presents significant opportunities for reduced flight testing but also comes with challenges when precisely simulating the flight environment. This paper introduces an innovative acoustic simulation model that leverages the Boundary Element Method (BEM) and a Direct Field Acoustic Testing (DFAT) simulation module. The primary objective is to virtually reproduce test sound fields that closely mimic the full fluctuating pressure environments aircraft encounter during flight using only loudspeaker arrays. This approach involves virtually reproducing a sophisticated test setup, typically comprising hundreds of drivers actively managed to generate a specific sound field. This setup is designed to virtually replicate various complex pressure environments, such as those produced by a Turbulent Boundary Layer, the complex pressure fields generated by aircraft propellers or jet engines. The use of active noise generation simulation helps determine the feasibility of a given pressure field and the capability of a test facility to simulate it accurately. The virtually reproduced sound fields simulated by this model show remarkable potential in approximating real-world pressure loadings. This capability is particularly useful in establishing pre-test predictions for fuselage testing such as sidewall build-ups: including insulation, and damping treatments, TVAs and TMDs.

Acoustic frequency-based method for high-speed aircraft combustion analysis and hybrid artificial intelligence diagnostics

In the paper, a method of high-speed continuous combustion monitoring for jet aircrafts, based on acoustic data processing, is proposed. As part of the research, acoustic signals corresponding to the specific phases of the combustible mixture formation and its combustion were separated. They were assigned to the generated process energy value. In the result, parametric functions were obtained in multidimensional spaces of states and processes. Parameters and acoustic characteristics in the amplitude, frequency and JTFA domains constituted information about particular symptoms in the jet engine, thanks to which reference waveforms of signals and forms for specific malfunctions were mapped. The above graphic characteristics have been parameterized to determine their diagnostic reliability factors.The method is verified by empirical signals obtained from turbojet propulsion system in time and power dependent conditions. Appropriate exothermic combustion phases were assigned for the determined acoustic spectra, taking into account the obtained power. Then, representative diagnostic parameters transformed in the process values domain were calculated. Finally, monitoring functions and algorithms of combustion efficiency with determination of malfunctions sources (at dynamic conditions) are proposed.As a result, it is possible to identify first outbreaks of design and process failures during fuel injection and combustion in aircrafts, taking into account artificial intelligence methods. The obtained results indicate it is possible to adapt the acoustic characteristics of the spectra and their discrete representatives, for appropriate states and failures, to detect first dangerous symptoms in the aircraft during flight conditions (supporting OBD with the acoustic adaptive diagnostic procedures).

Jet engines, wind turbines, and AI: community reactions to new sounds

When jet engine-powered commercial aircraft started flying in and out of airports in the mid-20th century, surrounding communities-often in rural areas-were exposed to unprecedented sound levels. A straight line can be drawn from the reactions of those communities to today's Federal Aviation Administration (FAA) airport acoustical requirements. Community reactions to utility-scale wind energy facilities in the late 20th and early 21st centuries led to a bevy of local legislation around the United States, some of which has been insightful and helpful. More recently, society's ever-increasing demand for bits and bytes is introducing suburban areas to data centers-campuses of multi-story buildings requiring access to high volumes of cool air, fast Internet connections, and megawatts of electricity. Community reactions to the resulting environmental sound levels are again driving regulation and legislation. In all these cases, community reactions have driven the narrative. Instead of responding to community reactions, the noise control engineering community and their clients could be more proactive-the professionals could lead the narrative. Ideas about how to achieve this level of proactivity are discussed.

Numerical Simulations and Experimental Validation of Squeeze Film Dampers for Aircraft Jet Engines

Squeeze film dampers are used to reduce vibration in aircraft jet engines supported by rolling element bearings. The underlying physics of the squeeze film dampers has been studied extensively over the past 50 years. However, the research on the SFDs is still ongoing due to the complexity of modeling of several effects such as fluid inertia and the modeling of the piston rings, which are often used to seal SFDs. In this work, a special experimental setup has been designed to validate the numerical models of SFDs. This experimental setup can be used with various SFD geometries (including piston ring seals) and simulate almost all conditions that may occur in an aircraft jet engine. This work also focuses on the inertia forces of the fluid. The hydrodynamic pressure distribution of a detailed 3D-CFD model is compared with the solution of the Reynolds equation including inertia effects. Finally, the simulation results are compared with experimental data and good agreement is observed.

Influence of the swirl vanes in convergent-divergent nozzle on screech tones and mixing efficiency at subsonic and supersonic jet flow

PurposeThe purpose of this study is to investigate the effect of coaxial swirlers on acoustic emission and reduction of potential core length in jet engines.Design/methodology/approachThe swirlers are introduced in the form of curved vanes with angles varied from 0° to 130°, corresponding to swirl numbers of 0–1.5. These swirlers are fixed in the annular chamber and tested at different nozzle pressure ratios of 2, 4 and 6.FindingsThe study finds that transonic tones exist for the nonswirl jet, creating an unfavorable effect. However, these screech tones are eliminated by introducing a swirl jet at the nozzle exit. Weak swirl shows a greater reduction in noise than strong swirl at subsonic conditions. In addition, the introduction of swirl jets at all pressure ratios significantly reduces jet noise and core length in supersonic conditions, mitigating the noise created by shockwaves and leading to screech tone-free jet mixing.Originality/valueThe paper provides valuable insights into the use of coaxial swirlers for noise reduction and core length reduction in jet engines, particularly in supersonic conditions.

Aircraft engine dust ingestion at global airports

Abstract. Atmospheric mineral dust aerosol constitutes a threat to aircraft engines from deterioration of internal components. Here we fulfil an overdue need to quantify engine dust ingestion at airports worldwide. The vertical distribution of dust is of key importance since ascent/descent rates and engine power both vary with altitude and affect dust ingestion. We use representative jet engine power profile information combined with vertically and seasonally varying dust concentrations to calculate the “dust dose” ingested by an engine over a single ascent or descent. Using the Copernicus Atmosphere Monitoring Service (CAMS) model reanalysis, we calculate climatological and seasonal dust dose at 10 airports for 2003–2019. Dust doses are mostly largest in Northern Hemisphere summer for descent, with the largest at Delhi in June–August (JJA; 6.6 g) followed by Niamey in March–May (MAM; 4.7 g) and Dubai in JJA (4.3 g). Holding patterns at altitudes coincident with peak dust concentrations can lead to substantial quantities of dust ingestion, resulting in a larger dose than the take-off, climb, and taxi phases. We compare dust dose calculated from CAMS to spaceborne lidar observations from two dust datasets derived from the Cloud–Aerosol Lidar with Orthogonal Polarization (CALIOP). In general, seasonal and spatial patterns are similar between CAMS and CALIOP, though large variations in dose magnitude are found, with CAMS producing lower doses by a factor of 1.9 to 2.8, particularly when peak dust concentration is very close to the surface. We show that mitigating action to reduce engine dust damage could be achieved, firstly by moving arrivals and departures to after sunset and secondly by altering the altitude of the holding pattern away from that of the local dust peak altitude, reducing dust dose by up to 44 % and 41 % respectively. We suggest that a likely low bias of dust concentration in the CAMS reanalysis should be considered by aviation stakeholders when estimating dust-induced engine wear.