Jet Engine Research Articles

Leidenfrost droplet jet engine by bubble ejection

HypothesisDespite the flourishing studies of Leidenfrost droplet motion in its boiling regime, the droplet motion across different boiling regimes has rarely been focused on, where bubbles are generated at the solid–liquid interface. These bubbles are probable to dramatically alter the dynamics of Leidenfrost droplets, creating some intriguing phenomena of droplet motion. ExperimentsHydrophilic, hydrophobic, and superhydrophobic substrates with a temperature gradient are designed, and Leidenfrost droplets with diverse fluid types, volumes, and velocities travel from the hot end to the cold end of the substrate. The behaviors of droplet motion across different boiling regimes are recorded and depicted in a phase diagram. FindingsA special phenomenon of Leidenfrost droplets that resembles a jet engine is witnessed on a hydrophilic substrate with a temperature gradient: the droplet traveling across boiling regimes repulsing itself backward. The mechanism of repulsive motion is the reverse thrust from fierce bubble ejection when droplets meet nucleate boiling regime, which cannot take place on hydrophobic and superhydrophobic substrates. We further demonstrate that conflicting droplet motions can occur in similar conditions, and a model is developed to predict the occurring criteria of this phenomenon for droplets in diverse working conditions, which agrees well with the experimental data.

Net-HDMR Metamodeling Method for High-Dimensional Problems

Abstract Metamodel technology provides an efficient method to approximate complex engineering design problems. However, the approximation for high-dimensional problems usually requires a large number of samples for most traditional metamodeling methods, which leads to the difficulty of “curse of dimensionality.” To address the aforementioned issue, this paper presents the Net-high dimension model representation (HDMR) method based on the Cut-HDMR framework. Compared with traditional HDMR modeling, the Net-HDMR method incorporates two novel modeling approaches that improve the modeling efficiency of high-dimensional problems. The first approach enhances the modeling accuracy of HDMR by using the net function interpolation method to decompose the component functions into a series of one-dimensional net functions. The second approach adopts the CV-Voronoi sequence sampling method to effectively represent one-dimensional net functions with limited samples. Overall, the proposed method transforms complex high-dimensional problems into fitting finite one-dimensional splines, thereby increasing the modeling efficiency while ensuring approximate accuracy. Six numerical benchmark examples with different dimensions are examined to demonstrate the accuracy and efficiency of the proposed Net-HDMR. An engineering problem of thermal stress and deformation analysis for a jet engine turbine blade was introduced to verify the engineering feasibility of the proposed Net-HDMR.

Hopf Bifurcations of Moore-Greitzer PDE Model with Additive Noise

The Moore-Greitzer partial differential equation (PDE) is a commonly used mathematical model for capturing flow and pressure changes in axial-flow jet engine compressors. Determined by compressor geometry, the deterministic model is characterized by three types of Hopf bifurcations as the throttle coefficient decreases, namely surge (mean flow oscillations), stall (inlet flow disturbances) or a combination of both. Instabilities place fundamental limits on jet-engine operating range and thus limit the design space. In contrast to the deterministic PDEs, the Hopf bifurcation in stochastic PDEs is not well understood. The goal of this particular work is to rigorously develop low-dimensional approximations using a multiscale analysis approach near the deterministic stall bifurcation points in the presence of additive noise acting on the fast modes. We also show that the reduced-dimensional approximations (SDEs) contain multiplicative noise. Instability margins in the presence of uncertainties can be thus approximated, which will eventually lead to lighter and more efficient jet engine design.

The turbulence models review for aerodynamic, thermal and structural problems in jet engine turbines.

Analysis of the aerodynamic, thermal and aeroelasticity (including vibration) processes in gas turbine stage is principal for a design and creating turbines and jet engine integrally. In this article was the review showed for the basic problems, which are solved by engineers for the gas turbines design and take a numerical analysis of flow. The special aspects was showed which appearance in the vanes and blades channels for turbojets turbine. The fundamental structure of the boundary layer and vortices on the low and high pressure faces of blade was demonstrated also. A target of this article is a review of current classification of the turbulence models and a review of best practices which include this turbulence models usage for the scientific and engineering problems. Authors describe the basic classification and the small specification with the application domain for each turbulence model (for aircraft). The general equation was demonstrated for URANS with a description of the Spalart – Allmaras, k-ε, k-ω, Menter’s SST, SST Gamma-ReTheta turbulence models. For LES, DES and DNS was showed description with the features only.The article contains the publications analysis with the turbulence models for three basic problems: aerodynamics, cooling problem (heat exchange) and structural problems (aeroelasticity, vibration resistance, stress limits, fatigue resistance). The turbulence models with high frequency of usage was presented in the current review moreover review contains the reasons of the models usage, the models hypothesizes, the changes of models (if it exists) and the solution accuracy. The solution accuracy was analyzed between different models of turbulence and between softwares for CFD. All arguments and conclusions was based on the different publications summary which was used for the review creating, and on data (numerical and graphical results) which was included in the researched CFD-articles. A little bit of the comparative analysis between CFD-softwares was created with the software’s user guides, the public reports and articles which includes the numerical researches in this problem. All results of the current review was presented in the general conclusions in end of article.

Microstructure and high temperature wear behavior of in-situ synthesized carbides reinforced Mo-based coating by laser cladding

To broaden the application fields of Mo coating as wear resistant coatings for hot-end components in jet engines, the in-situ synthesized carbides reinforced Mo-based coatings were prepared by laser cladding. The effect of nickel-coated graphite (carbon source) on the microstructure, hardness and elevated-temperature wear behavior of coatings was studied. The wear behavior of coatings was evaluated by using a tribotester with a ball-on-disc configuration from room temperature to 1000 °C against Si3N4 ball in air. The results showed that the carbides played a role of dispersion-strengthening. The coatings were composed of Mo, Cr1.12Ni2.88, Cr9Mo21Ni20, Mo2C, Cr7C3 and Mo6Ni6C. The wear resistance of the laser clad coatings was significantly enhanced by the addition of nickel-coated graphite, and the wear rates firstly decreased and then increased with increasing graphite content. The friction coefficients of laser clad coatings increased with an increase in nickel-coated graphite content. There existed a critical content of nickel-coated graphite that best strengthened the tribological behavior from room temperature to 1000 °C. The coating with 6.0 wt% nickel-coated graphite exhibited favorable tribological properties due to the moderate ductility, carbides, lubricating layer and in-situ synthesized solid lubricants.

ПОРІВНЯЛЬНИЙ АНАЛІЗ ЕНЕРГЕТИЧНИХ ХАРАКТЕРИСТИК РІЗНИХ ТИПІВ СИНХРОННИХ ТЯГОВИХ ЕЛЕКТРОДВИГУНІВ

Using the methods of mathematical modeling, a comparative analysis of the electromagnetic torque and power charac-teristics of three versions of traction synchronous motors was carried out: a synchronous jet engine, a hybrid synchro-nous jet engine with additional permanent magnets on the rotor, and a synchronous engine with permanent magnets installed on the rotor surface. The comparative analysis was carried out under the conditions of the same dimensions of the engines, the nominal values of the stator winding current and the speed of rotation of the rotor. It was established that under the given conditions, the synchronous motor with permanent magnets on the surface develops the greatest power and torque, but it also has the largest torque pulsations. Design measures to reduce torque pulsations at the same time led to a noticeable decrease in the nominal power of engines. The obtained results can be used when choos-ing an appropriate type of synchronous traction motor, taking into account the given compromise requirements for engine characteristics and vehicle operating conditions. References 12, figures 5, table 2.

Investigations on Oxidation Behavior of Free-Standing CoNiCrAlYHf Coating with Different Surface Roughness at 1050 °C.

MCrAlYHf bond coats are employed in jet and aircraft engines, stationary gas turbines, and power plants, which require strong resistance to oxidation at high temperatures. This study investigated the oxidation behavior of a free-standing CoNiCrAlYHf coating with varying surface roughness. The surface roughness was analyzed using a contact profilometer and SEM. Oxidation tests were conducted in an air furnace at 1050 °C to examine the oxidation kinetics. X-ray diffraction, focused ion beam, scanning electron microscopy, and scanning transmission electron microscopy were employed to characterize the surface oxides. The results show that the sample with Ra = 0.130 µm demonstrates better oxidation resistance compared to Ra = 7.572 µm and other surfaces with higher roughness in this study. Reducing surface roughness led to a decrease in the thickness of oxide scales, while the smoothest surface exhibited increased growth of internal HfO2. The β-phase on the surface with Ra = 130 µm demonstrated faster growth of Al2O3 compared to the γ-phase. An empirical model was suggested to explain the impact of surface roughness on oxidation behavior based on the correlation between the surface roughness level and oxidation rates.

Design optimization of composite fan blade in aircraft engine subjected to bird strike loading

Bird strike has been a perennial problem for all airline companies in the world. It is the most important design criteria for the fan blades of an aircraft engine. As it is not possible to manufacture and test aircraft engines again and again for small design changes, through the simulation analysis, it is possible to study the ways to reduce the impact of the bird on a jet engine by using appropriate design and manufacturing methods for the blade. This research suggests using two fibers (hybrid) in place of the single fiber composite blade which is currently in use to reduce the delamination issues. In the first stage of this research, representative composite coupon models for combinations of hybrid fiber joint positions were created and linear static analysis was performed. For the validation of simulation methodology, a few coupons were manufactured and tested in the laboratory. Further, dynamic bird strike analysis on sub-element level models was carried out in the second stage with various joint location combinations. Next, the plate-level representative blade model was designed with the original dimensions of the aircraft engine fan blade, and bird strike analysis was performed. The behavior of the representative plate with hybrid interface was studied, and the levels of inter-laminar shear strain were checked, by varying the joint location of the two composites. Some of the shortlisted cases do show significant promise of being damage tolerant under bird strike loading.

Reduced-Order Models Correlating Ti Beta 21S Microstructures and Vickers Hardness Measurements

Ti Beta 21S alloy is a metastable Ti Beta alloy commonly used in the aerospace industry, especially in jet engines. Components made from this alloy are usually subjected to various thermal histories during service, which leads to significant changes in their microstructures and associated mechanical properties. The central goal of this study is to demonstrate the feasibility of correlating the optical images of the microstructure obtained from heat-treated samples of Ti Beta 21S to their respective Vickers hardness measurements using recently established analyses and statistical quantification approaches based on the principal components of the rotationally invariant 2-point spatial correlations. The correlations extracted in this work can be used for non-destructive diagnostics of in-service components.

A guide to unmanned aerial vehicles performance analysis—the MQ‐9 unmanned air vehicle case study

AbstractGreat efforts are devoted for integrating Renewable Energy Sources (RES) on the propulsion system of Unmanned Air Vehicles (UAVs). This is applicable to small UAVs, having a horizon to expand to large UAVs within the next decades. For the conventional propulsion systems to be replaced, the required power needs of the aircraft should first be examined. The required power depends on the UAV's flight stage from takeoff to landing, whereas its calculation varies with regard to the propulsion system type, which is separated into two main categories, the propelled‐driven engines and the jet engines. Two obstacles are arising. First, the parameters needed for the power estimation are commercially sensitive and second the analysis alters with respect to the engine's type. This paper focuses on the mathematical analysis of the required power for both the main propulsion systems, presented extensively for each flight phase, proposing, at the same time, a parameter estimation method which is applicable to any UAV type. The main purpose of this paper is to act as a guide for the calculation of any type UAV's required power at any flight stage. To validate the analysis, the MQ‐9 Reaper/Predator B, a High Altitude Long Endurance (HALE) turboprop UAV produced by General Atomics is analysed. Its unknown parameters are estimated and based on a selected flight profile, the required power in terms of horsepower from takeoff to landing is assessed, for two scenarios regarding the aircraft's initial weight. In the first scenario the UAV has the maximum gross takeoff weight, whereas in the second scenario it does not carry any payload. The estimated required shaft power per flight phase for each scenario is then marked into the TPE331‐10 turboprop engine characteristic curves.

Estimation of fuel consumption in a jet engine based on vibration signal parameters

This paper proposes the use of vibroacoustic signal parameters to estimate the fuel consumption of a miniature GTM-400 engine. The method for testing engine vibrations is presented, followed by an analysis of the results obtained. Two vibration point measures were selected to build a fuel consumption model. The models obtained were verified, after which those that best describe the real fuel consumption of the engine were selected. The paper proves that the vibration signal, in addition to its applications in jet engine diagnostics, can be used to determine engine performance, which can contribute to reducing the complexity of construction and increasing the economics of engine operation.

Influence of welding parameters on mechanical and corrosion properties of Ti6Al4V alloy

Ti6Al4V is an alpha–beta grade 5 titanium alloy, which is the most commonly used of all the titanium alloys. Ti6Al4V alloy possesses a lot of desirable properties such as, weldability, heat treatability and resistivity against corrosion. Due to its outstanding strength-to-weight ratio and low modulus of elasticity it is widely used in jet engines, aircraft fuselage and defence armour. In this investigation, an effort has been made to determine the optimal welding parameters in welding of 3 mm thick Ti6Al4V alloy plate using Gas Tungsten Arc Welding – with filler (GTAWF), Gas Tungsten Arc Welding – Autogenous (GTAWA) and Laser Beam Welding – Autogenous (LBWA) techniques and weldability of Ti6Al4V alloy. The GTAWF, GTAWA and LBW techniques are fusion welding techniques having the welding input parameters as Voltage V (volts), Current I (ampere) and Feed F (mm/minute). The response from these welding processes are Tensile strength T (MPa), Joint efficiency η(joint)(percent), Impact strength I (Joules) and Corrosion rate CR (mils/yr). The optimal welding parameters were determined with condition that the welding parameters had high mechanical properties (tensile strength, joint efficiency, impact strength) and minimum corrosion rate. The optimal welding parameters yielded GTAWF weldments that exhibited relatively excellent mechanical properties and corrosion resistance compared to LBWA, whereas GTAWA weldments exhibited a mediocre performance.

Non-destructive evaluation of GTAWA, GTAWF and LBWA welded Ti6Al4V alloy

Ti6Al4V is the most commonly used titanium alloy which features high strength with low density, high fracture toughness, excellent resistance against corrosion and good weldability. Ti6Al4V finds wide application in variety of sectors such as aircraft structure, jet engines, gas turbines, defence armour and IC engine components. The quality of the titanium weldments is significant in producing titanium structures and components. This requires critical Non-Destructive Testing (NDT) procedures to be followed. There is very scarce literature reported on NDT of titanium weldments. In this investigation the Non-Destructive Testing of Ti6Al4V weldments welded using Gas Tungsten Arc Welding – Autogenous (GTAWA), Gas Tungsten Arc Welding – with filler (GTAWF) and Laser Beam Welding – Autogenous (LBWA). The weldments were subjected NDT procedures such as visual and X-ray radiography. The uniqueness of this study is that the Image Quality Indicator (IQI) of aluminium was used as the IQI for titanium is not available in the industries. Generally, the titanium gets contaminated by gases in the atmosphere, leading to loss of mechanical strength and corrosion resistance of the weldment. Hence in this investigation a novel approach for ruling out the contamination of the weld pool and the Heat Affected Zone (HAZ) has been proposed viz. Weld Quality Indicator (WQI), i.e. the discolouration on the surface of the weldment is taken as an indicator of the contamination.

Visual analysis of the impact of periodic wakes on the pressure side of a turbine blade

Turbines are core components in jet engines for flight propulsion, power plants, and other important energy conversion processes. They are composed of successive rows of blades so that wakes of upstream blades reach subsequent blades where they perturb the flow in an unsteady manner. At the point where a wake reaches the downstream blades, the perturbation forms a so-called negative jet. In this work, we show that the negative jet partially fulfills the conditions of an anti-splat. Based on this finding, we enhance an anti-splat detection algorithm developed by the present authors in previous work and apply it to direct numerical simulation data of a turbine cascade with unsteady wakes. This provides a sound framework and suitable visualization approaches to investigate the phenomenon even in very complex conditions, as is the alteration of the boundary layer flow along the pressure side of a turbine blade. The approach allows a very clear visualization of this interaction, which was not possible to evidence with previous methods, providing new insight into the physics of this flow. The use of flow paths shows up to which point wakes affect the boundary layer along the blade. The reported physical analysis, made possible by the proposed approach, demonstrates the usefulness of the method for the application domain. The generalization to flows in compressors, pumps, and blade-tower interaction in wind engineering and other fields is possible.Graphical abstract

Health monitoring of the shaft bearings in a micro turbojet based on vibration analysis

In a recently implemented aerial target, the propulsion system consists of two JetCat micro turbojet engines. Due to the limited durability of the rotor support bearings, the engine operation time has been limited to two hours or two flights. In addition, after each flight, an engine bench test with vibration measurement is required. The adopted maintenance system is also labor-intensive and costly due to obligatory shaft bearing inspections performed frequently in the repair shop. These problems result from the limitations of the available high-speed bearing technology and the high rotor loads related to aircraft maneuvers in the air. The goal of the work is to develop a method for assessing the health of the main shaft bearings in the micro turbojet based on vibration signals. Methods known from full-scale jet engines were adapted for monitoring the health of the main shaft bearings. An accelerometer and rotational speed sensor were mounted on the engine. Vibration and other parameters of the engine were measured and analyzed, and then symptoms of damage were sought. The vibrations of seven JetCat engines were analyzed, selecting the one for further destructive testing. In all three axes X, Y and Z, the vibration components related to the rotational frequency and its orders are dominant, especially EO2 and EO3 related to rotor dynamics. Continuous engine vibration monitoring is a promising way of extending engine life and avoiding the deficiencies of microturbines related to their size and low-cost technology. The obtained results indicate that the tested JetCat engines have a life reserve, which has so far been used to a small extent.

Extensive Lunar Surface Disturbance at the Chang'e‐5 Mission Landing Site: Implications for Future Lunar Base Design and Construction

AbstractLunar surface disturbances by spacecraft engine jets are of particular concern in the current new phase of lunar exploration, when dozens of landing missions and permanent bases are being planned. Some of these exploration efforts will involve multiple landings and liftoffs around the same lunar site; thus, it is essential to evaluate their effect on astronauts and assets on the lunar surface. Here, we assess the surface disturbances during the Chang'e‐5 landing and liftoff procedures through the photometric analysis of high‐resolution multi‐temporal surface and orbital images. Centimeter‐scale surface images reveal a four‐stage evolution of the landing plume impingement over a period of ∼50 s, which involves phenomena such as dust devils and streaks, and displacement of cobbles. Temporal‐ratio calculation of orbital images (including one acquired between landing and liftoff) enables the first direct observation of ascent plume effects. The ascent blast zone consists of two separated sub‐areas (∼3,400 m2 in total), which is nearly twice larger than that of the landing blast zone. The final disturbed surface is characterized by a central main zone (∼2,300 m2) surrounded by a marginal diffuse zone (∼15,300 m2). Phase‐ratio analyses suggest that plume impingement destroys the micro‐porous structure of the uppermost regolith. We estimate that future lunar landers (e.g., SpaceX's Starship) may cause significant lunar surface disturbances over an area of square kilometers. Our results provide unique insights into Chang'e‐5 mission activities, and instructive references for the planning of future lunar endeavors, including the design and construction of surface experiment packages and permanent lunar bases.

Effect of the hydrogen/kerosene blend on the combustion characteristics and pollutant emissions in a mini jet engine under CDC conditions

In this CFD study conducted with the geometry of a mini gas turbine engine using kerosene as fuel, colorless distributed combustion conditions were achieved by increasing the N2 ratio in the air. Then, H2 was added to the kerosene fuel in order to increase the combustion performance and the combustion chamber temperature distributions, NOx, CO, and CO2 values were examined. In the simulations using the simplified GTM-120 geometry, the combustion chamber outlet temperatures at 80 k, 100 k, and 120 k rpm were compared with the experimental results in the literature by changing the ratio of fuel and air for the validation study. Standard k-ε and Discrete Ordinates were chosen for turbulence and radiation models, respectively. In the study conducted with the non-premixed combustion model, simulations were made at O2 rates of 21%, 19%, 17%, and 15% for the formation of colorless distributed combustion conditions. For enrichment with hydrogen, H2 was added from 0% to 50% with 10% increments. HEF (Hydrogen energy fraction) has been used as the hydrogen addition rate. In light of the analyses made, it was seen that the colorless distributed combustion regime reduced the flame temperature from 2292 K to 1912 K and the NOx amount from 2.85 ppm to 0.0086 ppm. On the other hand, it is seen that this regime increased the CO emissions from 6.9 ppm to 38.67 ppm and the mole ratio of CO2 from 6.25% to 6.94%. It was observed that these findings prepared the ground for increasing the amount of hydrogen in the fuel, which increases the flame temperature and, accordingly, NOx emissions. By adding 50% H2 to kerosene under standard atmospheric conditions, the average NOx emission at the combustion chamber outlet increased from 2.85 ppm to 7.97 ppm, while the average CO emission decreased from 6.9 ppm to 1.08 ppm. As a matter of fact, by the addition of 50% H2 to the kerosene with air that contains 15% O2, which is the most extreme combustion situation in this study, the flame temperature decreased to 1912 K, and NOx rose to 0.0713 ppm. However, the CO emissions at the combustion chamber outlet decreased to 1.83 ppm and the CO2 ratio to 3.48%. Thus, with this study, it has become possible to use hydrogen as an alternative fuel in a real engine geometry by using CDC and hydrogen enrichment together, both in terms of pollutant emissions and combustion performance.

Analysis and Possible Improvements of Scramjet Engines: The Effective Thrust and the Combustion Stability Problems

The scramjet is the representative of the future jet engine, and it has irreplaceable advantages in terms of working performance and service life. Although it has been developed more than fifty years, there are many problems in the driven system of the scramjet engine. This paper mainly focuses on the problems of the effective thrust and the combustion stability. The research shows that how the pressure ratio affects the positive thrust and the combustion stability. Furthermore, this paper also shows that the elements which can affect the pressure ratio. The lower inlet air temperature is beneficial to enhance the thrust. According to the relevant research which apply the CJ detonation theorem to find the possible reason for the combustion instability. For the possible improvements, the research found that the engine thrust at different speed and the allowable maximum speed. The type of fuel and the reactivity of the fuel can influence the thrust.

Off-design performance of micro-scale solar Brayton cycle

A novel methodology to design a micro-scale, solar-only, air-breathing, open Brayton cycle and assess its on- and off-design performance. The methodology is applied to generate and assess six thermodynamic layouts over a range of solar irradiation levels. All plants have the same on-design requirements to create a baseline to compare their off-design performance. PyCycle, a thermodynamic cycle modeling library to model jet engine performance, is revised to transform the jet engine performance modeling to solar thermal plant performance modeling and used to create a volumetric receiver component. A response surface surrogate model of the receiver is created for design optimization to maximize the component-level efficiency. The compressor and turbine maps are scaled for the balance of the plant. Off-design efficiency, mass flow rate, operation range, turbomachinery maps, and maximum power output are presented. Since the methodology can be adapted to all plant sizes, the results are normalized to on-design condition. The outcome of this study demonstrates the impact of the thermodynamic configuration on off-design performance and provides a methodology to design plants that are more robust across a range of solar irradiation levels and can be operated in a more flexible manner. Compared to single shaft configuration, solar radiation operation range is improved by 5%, with 6% less mass flow, and operates more efficiently than the benchmark case over 85% of the operating regime.

Creep–Fatigue Interaction of Inconel 718 Manufactured by Electron Beam Melting

Electron beam melting of Ni‐base superalloy Inconel 718 allows producing a columnar‐grained microstructure with a pronounced texture, which offers exceptional resistance against high‐temperature loading with severe creep–fatigue interaction arising in components of aircraft jet engines. This study considers the deformation, damage, and lifetime behavior of electron‐beam‐melted Inconel 718 under in‐phase thermomechanical fatigue loading with varying amounts of creep–fatigue interaction. Strain‐controlled thermomechanical fatigue tests with equal‐ramp cycles, slow–fast cycles, and dwell time cycles are conducted in the temperature range from 300 to 650 °C. Results show that both dwell time and slow–fast cycles promote intergranular cracking, gradual tensile stress relaxation, as well as precipitate dissolution and coarsening giving rise to cyclic softening. The interplay of these mechanisms leads to increased lifetimes in both dwell time and slow–fast tests compared to equal ramp tests at higher strain amplitudes. Conversely, at lower mechanical strain amplitudes, the opposite is observed. A comparison with results of conventional Inconel 718 indicates that the electron‐beam‐melted material exhibits superior resistance against strain‐controlled loading at elevated temperatures such as thermomechanical fatigue.