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This paper aims to determine the relationship between thermodynamic entropy generation and fatigue crack propagation life of superalloy GH4169 at 300–650°C. The entire specimen was considered as the thermodynamic system. The plastic energy dissipation in the crack tip was obtained by finite element simulation utilizing the Chaboche nonlinear hardening model. Then the cyclic entropy generation rate (CEGR) and the accumulated entropy generation are calculated by combining simulation and experimental methods. Results show that the CEGR is a power function of the stress intensity factor range, and it is almost a constant at fatigue failure. The fatigue fracture entropy (FFE) increases as fatigue cycles at failure increase at constant temperature, but it first decreases and then increases when temperature increases from 300 to 650°C. A fatigue life prediction model based on the thermodynamic damage parameter is established and verified by comparison with experimental results and available data in the literature. Highlights: Thermodynamics provides a new thought to the study of elevated temperature crack growth.The Chaboche nonlinear hardening model is considered in entropy generation calculation.An entropy‐based damage parameter can represent the damage of a thermodynamic system.Entropy‐based life prediction model can acceptably predict the crack propagation life. [ABSTRACT FROM AUTHOR]

This paper develops a thermodynamic entropy-based life prediction model to estimate the low-cycle fatigue (LCF) life of the nickel-based superalloy GH4169 at elevated temperature (650 °C). The gauge section of the specimen was chosen as the thermodynamic system for modeling entropy generation within the framework of the Chaboche viscoplasticity constitutive theory. Furthermore, an explicitly numerical integration algorithm was compiled to calculate the cyclic stress–strain responses and thermodynamic entropy generation for establishing the framework for fatigue life assessment. A thermodynamic entropy-based life prediction model is proposed with a damage parameter based on entropy generation considering the influence of loading ratio. Fatigue lives for GH4169 at 650 °C under various loading conditions were estimated utilizing the proposed model, and the results showed good consistency with the experimental results. Finally, compared to the existing classical models, such as Manson–Coffin, Ostergren, Walker strain, and SWT, the thermodynamic entropy-based life prediction model provided significantly better life prediction results. [ABSTRACT FROM AUTHOR]

Straight-through labyrinth seal is a simple and reliable noncontact seal structure widely used in aeroengines. During the actual operation of aeroengines, the labyrinth seal clearance might experience a nonuniform variation in the flow direction due to asymmetric structure and uneven temperature. In order to characterize the degree of nonuniformity, the nonuniformity coefficient is defined in current paper. The effect of nonuniform causes (rotor deformation or stator deformation), nonuniform type (convergent clearance or divergent clearance), and nonuniformity coefficient (nonuniformity degree) is carefully studied by numerical simulation. Comparative analysis has shown that there is no obvious difference in flow coefficient (less than 0.8% in current studies) between two nonuniform causes. As for nonuniform type, the nonuniformity impact of divergent type on the flow coefficient is more significant than that of convergent type, as a result of stronger axial inertia. Pressure distributions of teeth cavities indicate that the total pressure drop of the divergent type is more obvious than that of the convergent type when the pressure ratio is the same. With the same dimensionless minimum tip clearance, clearance nonuniformity would result in the increase of leakage flow of the straight-through labyrinth, particularly for the condition with small pressure ratio, large circumferential Mach number, and small dimensionless minimum tip clearance. When the nonuniformity coefficient is within the range of -0.1 to 0.1, the variation curves of nonuniformity impact factor versus the nonuniformity coefficient almost coincide (the maximum deviation is no more than 1.2%) under different operation conditions (Reynolds number, pressure ratio, circumferential Mach number, and dimensionless minimum tip clearance). Current work proves it that the effect of seal clearance nonuniformity on the leakage flow requires special attention for the refined design of aeroengines. [ABSTRACT FROM AUTHOR]

Poly(3,4‐ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT: PSS) core–shell conductive atypical spiral microfibers are prepared based on microfluidic spinning technology (MST). The formation mechanism of the special‐shaped spiral structure is analyzed. The microfibers and polydimethylsiloxane (PDMS) are composited into membranes, and the microfibers and composite membranes are characterized. The research results show that the conductivity of shell conductive bulbine‐torta (BT) microfibers and the composite membrane are 0.125 1 and 0.880 2 s cm−1, respectively. The maximum strain of a single PEDOT: PSS core–shell conductive BT microfibers is 36.92% under a stress of 213.10 kPa, and the maximum strain of the composite membrane is 107.46% under a stress of 470.56 kPa, indicating that the composite membrane can effectively improve the properties and practicability of the conductive fiber. The change of resistivity of the composite membrane in the stretched state is observed, and it is found that the resistivity first steadily increases and then increases exponentially, indicating that composite membrane has potential application prospects in the fields of thin membrane sensors, electronic skins, smart wearable textiles, etc. [ABSTRACT FROM AUTHOR]

From a system perspective, the entropy generation of an aeroengine is directly related to the thermal efficiency when the Brayton cycle pressure ratio and maximum temperature remain constant. The lower the entropy generation of the engine is, the higher the thermal efficiency. However, the secondary air system of the engine generates a large quantity of entropy compared to the components of the main flow channel, because the irreversible losses of the internal flow and heat exchange between the air system components generate considerable entropy within the system. In this study, the theoretical method is used to build entropy generation model for different characteristics of air system components during the aerothermal process. In this basis, an integrated model of the whole engine is introduced to identify the key components for entropy generation in the system environment. The results show that the labyrinth at outlet of unloading cavity is recognized as the one that generates the most entropy in the entire aeroengine system, and the total entropy generation of the system is highly related to this component. Besides, in the system environment, entropy generation is the sum of the local entropy generated by the components and the total entropy generated by mixing of airflows in each component. High local entropy generated by components does not necessarily result in a high system entropy production, and vice versa. Therefore, when the minimum system entropy generation is the design goal, the most critical operations for entropy generation should be identified according to the corresponding sensitivity and parameter variation range, and the design should be improved accordingly. [ABSTRACT FROM AUTHOR]

Labyrinth seals are widely employed in the air system of aircraft engines since they reduce the leakages occurring between blades and shrouds, which affect the entropy generation significantly. Excessive leakage flow of the labyrinth may be reduced the efficiency and performance of the engine. This paper proposes the concept of flow-resistance-increasing vortex (FRIV) on the top of the labyrinth that is based on the flow entropy generation mechanism of the stepped labyrinth and the main flow characteristics that lead to entropy generation. A three-dimensional simulation model of the labyrinth structure was established, and the model was compared and verified with the experimental data of the reference. The relative dissipation strength and vorticity distribution of the FRIV were theoretically analyzed. It was confirmed that the dissipative intensity distribution was the same as the vorticity distribution, and the correlation coefficient was larger in the labyrinth tip region. Therefore, a parametric study was conducted on design parameters related to the FRIV, including the teeth inclined angle, tooth crest width, step inclined angle, and other parameters. The results are beneficial for the construction of a stronger FRIV to reduce the leakage. This research is of great significance for the improvement of engine efficiency and for the reduction of fuel consumption in the future. [ABSTRACT FROM AUTHOR]

Straight-through labyrinth seals are reliable noncontact seal structures widely used in aeroengines. Windage heating and swirl development of labyrinth seals are of great significance to the design of secondary air systems. In the operation process of an aeroengine, a labyrinth seal is supposed to experience uneven temperature distribution, which may cause deformation and resulting nonuniformity along the flow direction. The nonuniformity coefficient was defined to characterize the degree of nonuniformity so that the influence of nonuniform clearance on windage heating and swirl development can be analyzed quantitatively. Windage heating and swirl development were analyzed from the perspectives of different Reynolds numbers, pressure ratios, circumferential Mach numbers, and dimensionless minimum tip clearances. Simulation results showed that when other dimensionless parameters are the same, both windage heating number and exit swirl ratio decrease with the increase of the nonuniformity degree. With the same nonuniform degree, the decrease rate of divergent clearance is larger than that of convergent clearance. The changing trends of the decrease rate of both windage heating number and exit swirl ratio were analyzed in detail. It can be concluded that the decrease rate of the exit swirl ratio reaches the peak when the dimensionless minimum tip clearance is about 0.067. This result makes it clear that the effect of nonuniform clearance is indispensable for the safety assessment of aeroengines. [ABSTRACT FROM AUTHOR]

In probabilistic failure risk assessment, the accuracy and efficiency of the stress intensity factor calculation are important. The universal weight function method has been widely adopted for efficiency, but this method still has some debatable parts. For accurate and efficient stress intensity factor prediction, two approaches for machine learning techniques are specially designed. Three tests are conducted for the first approach where Gaussian process regression, tree‐structure models, and artificial neural network are evaluated and compared for the ability of interpolation and extrapolation. Results show that the artificial neural network and extremely randomized trees perform better. Hybrid models in the second approach are also proposed, and results show that the accuracy of SIF calculation can be improved by 5–35% compared with the weight function. Real aeroengine disks are adopted, and the errors of machine learning methods are less than 20% in the disk life calculation. [ABSTRACT FROM AUTHOR]

Turbocharging is an effective way to address the problem of reduction in power and increase in fuel consumption of aviation piston engines during high-altitude flight. However, turbochargers have greatly increased the degree of complexity of power systems. The model-based system safety analysis methods for the safety analysis of turbocharging systems are introduced in this study to overcome the limitations of the traditional safety analysis methods regarding complex matching and coupled safety issues. On the basis of the established system models and the formed failure mode work boundaries and safety boundaries, the column profile coordinates F of correspondence analysis with the numerical deviation of the key factors are used to identify the key factors affecting failure, thereby proposing safety control strategies in a targeted manner. Then, the failure probability of the turbocharging system is assessed through the Monte Carlo method. System failure modes and probabilities before and after the execution of safety control strategies are compared to accurately determine the effectiveness of those strategies. The verification examples show that a safety control strategy that adjusts the diameter of the wastegate e 2 can reduce system failure probability and enhance safety level. [ABSTRACT FROM AUTHOR]

• Finite element method for calculating material entropy generation based on the viscoplastic UMAT. • An entropy-based crack driving force was proposed within defined fracture process zone (FPZ). • A crack growth criterion based on cumulative entropy generation as crack grows a length of FPZ. • An entropy-based model was proposed to predict fatigue crack growth in GH4169 at high temperature. This paper developed an entropy-based approach to estimate the fatigue crack growth (FCG) behavior of GH4169 at high temperature. Firstly, systematic FCG experiments of GH4169 at 650 °C were conducted to obtain the experimental data. Then, a finite element analysis combined with Chaboche viscoplasticity and node release technology was developed to obtain cyclic stress–strain responses and entropy generation fields. Based on thermodynamic analysis, numerous discrete material elements as sub-systems were divided along the crack growth direction in simplified representative 2D middle section. Fracture process zone (FPZ) was defined equal to the size of discrete material elements (ρ) which can be determined by distribution of normal stress perpendicular to the crack plane. Subsequently, an effective cyclic entropy generation related to ρ was defined as the crack driving force. Effective cumulative entropy generation was calculated when crack increment was ρ and the results indicated that effective cumulative entropy generation float within a certain range. The average of all effective cumulative entropy generation values was defined as crack growth entropy. Finally, an entropy-based FCG rate model was established to estimate the FCG behavior of GH4169, and a good correlation between experimental results and model predictions are achieved for all the high temperature FCG tests. [ABSTRACT FROM AUTHOR]

• Providing time-resolution for aerothermal-mechanical system safety analysis. • System model contains inertia effects to reflect dynamic characteristics. • Fault model incorporates modules for time-related parameters. • Identifying Safety Critical Parameters for quantitative safety analysis. • Fault injection is achieved through data transfer between models each time step. Current aero-engine safety assessments mostly rely on experience-based safety analysis methods such as Fault Tree Analysis (FTA) or Failure Modes and Effects Analysis (FMEA). The progressively significant dynamic characteristics of aero-engines during their transition between states render these methods incapable of providing accurate quantitative safety guidance, which is vital for complex aerothermal–mechanical systems. To solve this problem, a Model-Based Safety Analysis with Time Resolution (MBSA-TR) method was established, which included system modeling, fault modeling, and Safety Critical Parameter (SCP) identification. An integrated system model combining the main gas path and air system was built based on dynamics principles, and it was capable of reflecting the dynamic characteristics of aero-engines. The fault model included several time-resolved sub-modules and interacted bidirectionally with the system model at each time step to realize time-sequential fault propagation. SCPs were defined as parametric analysis objectives, and they were identified using an FTA-like identification framework. Finally, a case study of a typical turbofan engine with low-pressure compressor blade fractures as the primary fault was analyzed. The results showed that some hazard risks are incapable of detection without time resolution. Thus, time resolution is indispensable for the safety evaluation of complex aerothermal–mechanical systems of aero-engines. [ABSTRACT FROM AUTHOR]

In this article, we start with the spatial dispersion difficulty encountered in the solution of physical phenomena controlled by partial differential equations. The one-dimensional diffusion phenomenon is taken as the research object, and the optimal precision that can be achieved under the theoretical grid number is obtained by programing. And a sensitivity analysis method for spatial discrete optimization with no analytical solution is proposed and evaluated. At the same time, this paper takes the non-adiabatic single-pore cavity of typical components in the research of aero engine air system network as an example, and applies the above method to the calculation of strong nonlinear fluid. We find that the optimal spatial discrete method obtained by applying the sensitivity method explored in this paper is at least seven times more efficient than the experience-based meshing method. [ABSTRACT FROM AUTHOR]

One of the key processes for safety design of aeroengines is to accurately predict the failure risk of aeroengine disks. Current risk assessment methods mostly based on a constant stress are suitable for steady-state analysis but inappropriate for dangerous transient process. This work proposes a method of probabilistic failure risk assessment for aeroengine disks considering a transient process, and the core procedure is zone definition through refinement and further partition of a constant pre-zone based on the time-varying stress in a flight cycle. An aeroengine compressor disk is analyzed, and the failure risks of the disk considering a transient process and based on a steady-state design point are compared to examine the influence of the transient process on the failure risk of the disk. Results show that the failure risk considering the transient process is approximately 3.7 times of that based on the steady-state design point because the peak stress of the disk during the transient process exceeds the steady-state stress. The proposed method obtains more accurate predictions of failure risk, and is thus valuable for the safety design of aeroengines. [ABSTRACT FROM AUTHOR]

The effect of actively managed thermal loading for optimal design of turbine disk was investigated to seek the better balance between strength demand and minimum weight/volume. An integrated process of design was developed to achieve automatic iteration for this multi-objective optimization problem. Under equal consumption of heating energy and cooling air conditions, two types of actively managed thermal loading with different allocation ratios of heating energy ( ϕ = 0.1 and ϕ = 0.2) in the outer and inner surface of disk were considered in the process of optimization. As a comparison, the disk at conventional thermal loading conditions ( ϕ = 0) was also optimized at the same design conditions. Results showed that the better structure of disk with smaller weight/volume and lower maximum stress level was obtained due to thermal loading management. Through actively managing the thermal loading to reorganize the temperature distribution of disk, the optimized weight/volume and maximum hub stress fallen 2.24% and 12.16% respectively to compare with the conventional thermal loading condition. The reason for the preceding effect could be explained that an artificial V-shaped temperature distribution was built in the disk through actively managing thermal loading, and correspondingly, the reverse temperature gradient between hub and web produced a pulling effect and counteracted parts of stress from rotating. [ABSTRACT FROM AUTHOR]

Online onboard aeroengine models (OBEMs) have been widely used in health management, fault diagnostics, and fault-tolerant control. A mismatch between the OBEM and the actual engine may be caused by a variety of factors such as health degradation or sensor fault and may influence the effectiveness of the systems mentioned above. However, mismatch caused by unpredictable sensor fault is hardly distinguished from that caused by health degradation through the tuning process. A fault-tolerant OBEM tuning structure is provided to perform the online tuning function when health degradation and sensor fault coexist. This system includes three parts that include improved fault diagnostics and isolation (IFDI), a fault-tolerant OBEM tuning system (FTOTS), and a channel switching module. IFDI is used to distinguish the cause of mismatch and provide fault information, a FTOTS is used to complete an online tuning process based on information obtained from the IFDI, and the channel switching module is used to switch the working process from the IFDI to the FTOTS. Several simulation results show that this system is able to distinguish the causes of mismatch and complete online tuning in the case of sensor faults. [ABSTRACT FROM AUTHOR]

Hydrogen is a clean energy carrier for energy storage which is essential to solar system for continuous energy output. A promising method to store solar energy as hydrogen energy is by using photovoltaic-electrolyser (PVE) system. In this investigation, the operation of a PVE system with V-trough concentrator was studied experimentally and numerically. The V-trough concentrator was optimized and the daily average concentration ratio reaches about 1.9. A mathematical model including the sub models for irradiation flux pattern, PV array and electrolyser was established to analyze the characteristics of the system and it was verified experimentally. The results show that the utilization of V-trough concentrator makes PVE system work more efficiently with the same PV array. In this study, the conversion efficiency of solar energy to hydrogen energy was increased from 5.62% to 6.18% and the hydrogen production was doubled. [ABSTRACT FROM AUTHOR]

From the point of view of the physical essence, using cooling technology in turbine systems is a process of energy management and the developed cooling structure in the last forty years is aimed at carrying out a different energy management strategy. Based on this idea, in this paper the energy management strategy for each cooling structure was abstracted first and reflected by parameters of heating energy Q e in the outer surface, exchanged energy Q in in the inner surface and wall heat transfer coefficient h of the disk. Then, the influences of energy management strategy on stress state of near real geometry of the turbine disk were investigated. That is, the equation correlating different energy management strategies with stress states for disks was built by theoretical analysis and the computational fluid dynamics and finite element simulations were applied to validate the theoretical analysis. Results showed that the stress state could be effectively controlled through actively adjusting the energy management strategy. And under a constant cooling structure and equal consumption of cooling air and heating energy conditions, the heating energy of disks could be rearranged (reflected by allocation ratio of heating energy ϕ ) in outer ( Q e ) and inner ( Q in ) surface to achieve the actively heated hub of the disk, and the resulting decline ratio of maximum equivalent stress level in hub could be arrived 45.52% at ϕ = 0.20 to compare with the conventional energy management strategy ( ϕ = 0 ), even in 3981 rpm. The reason for the preceding effect was explained by an artificial V-shaped temperature distribution that was established in the disk through actively rearranging the heating energy and correspondingly, the reverse temperature gradient between the hub and web produced a pulling effect and counteracted parts of the stress from rotating. In general, the simulation data were in strong agreement with the above results. [ABSTRACT FROM AUTHOR]

Abstract: Hydrogen as a clean energy carrier for solar energy can be produced by using photovoltaic-electrolyser (PVE) direct-coupling system that is well known as a kind of simple and low investment but unstable system for solar energy conversion. The key to improve hydrogen yield of a direct-coupling system is to keep its working points around maximum power point (MPP) of photovoltaic (PV) modules. The coupling of three different connection patterns of six PV modules with one electrolyser were investigated in summer, autumn and winter, three typical seasons in a year, to seek the optimum arrangement for higher system efficiency in Beijing (116°E, 40°N). A corresponding mathematics model of the system is applied to simulate and analyze the instantaneous efficiency of the system, which agreed well with the experimental results. The variation rate of the system instantaneous efficiency varies with the solar irradiation intensity, the ambient temperature and the resistance of the electrolyser. The working point that distinguishes the variation trends of the system efficiency is called the efficiency changing point (ECP). The author use a parameter V/V m , the ratio between the voltage of the working point to the voltage of the maximum power point, to analyze the respective ECP of each factor above. It can be concluded that the variation rate of system instantaneous efficiency changes little with the above factors when the value of V/V m of working point is smaller than that of the ECP and is sensitive to those factors when the value of V/V m is larger than that of the ECP. Following the annual historical climate data in Beijing, the result of the annual analysis is that the best scheme for the experiment system with a 1 m2 PV panel covering 1.05 m2 areas of ground can convert 78.4 kWh of solar energy to hydrogen energy in 2012. [Copyright &y& Elsevier]

An equivalent model using Taylor expansion (TEEM) is proposed for a fleet of engines regulated by the industrial baseline controller, aiming at the fast assessment of in-service thrust control under gas path and measurement uncertainties in advance. TEEM is fulfilled initially by the equivalent transformation of measurement uncertainties into engine set-point distribution, followed by a first-order Taylor expansion on the steady-state aero-thermal engine model along the average degradation curve of engine fleets. Simulations are conducted at take-off states on a validated aero-thermal turbofan engine model with publicly available uncertainty statistics on a desktop computer. Results show that the equivalent transformation is successful for both new and degraded engine fleets. Moreover, TEEM can estimate the mean and standard deviation values of key engine control parameters including thrust with the maximum errors of 0.04 % and 3.85 % for new engine fleets, 0.04 % and 6.25 % for degraded engine fleets, respectively, compared to the classic sample-based Monte-Carlo simulations (MCS). Computational time for TEEM and MCS for the tested life cycle are 3,018,564s and 137.52s accordingly, which means 99.995 % simulation time reduction is achieved by TEEM. Hence, the accuracy and efficiency of the proposed model for uncertainty assessment of thrust control of turbofan engines are confirmed. • An equivalent model using Taylor expansion for fast uncertainty assessment. • Transforming measurement uncertainties into engine set-point distribution. • Taylor expansion implemented along the average degradation curve of engine fleets. • Probablistic distribution of key engine control parameters are accurately estiamted. • Assessment time is significantly reduced for new and several degraded engine fleets. [ABSTRACT FROM AUTHOR]

The secondary air system of a gas turbine engine is a complex fluid network that is sensitive to geometric variations in the flow elements caused by manufacturing, assembly, and operating conditions. Geometric uncertainty of the flow elements is a major cause of secondary air system failure. To reduce the performance uncertainty due to geometric uncertainty, this paper constructs a probabilistic analysis method that couples the primary air system and the secondary air system and proposes a robust optimization mathematical model for the rotor axial bearing loads of the secondary air system, using the control of the rotor axial bearing loads as an example. A case study is presented to demonstrate the application of the proposed robust optimization method in controlling the scatter of axial bearing loads. Probabilistic analysis and sensitivity analysis are performed for the original design scheme and the robust optimization design scheme of the secondary air system. The results show that the standard deviation of the high-pressure axial bearing loads in the robust optimization design scheme is 72.9% lower than that in the original design scheme under the same uncertainty distribution of the labyrinth clearance. In addition, the sensitivity of the axial bearing loads to the labyrinth clearance is reduced. Thus, it is demonstrated that the proposed robust optimization method can effectively reduce the functional scatter and the sensitivity to geometric variations in the gas turbine secondary air system. [ABSTRACT FROM AUTHOR]

• A standardized method for predicting the safety of complex mechanical systems during the design stage is proposed and illustrated with an aviation piston engine. • Quantifying the safety of the entire system through a standardized procedure improves consistency between different assessment. • Multidimensional coupling of indexes characterizing different subsystems is considered to achieve the quantification of inter-subsystem associations from the perspective of the entire system safety. • Proposed method could improve the design for complex mechanical systems based on safety feedback, especially related to specialized research such as piston engines, safety analysis could be extended based on the previous design. Conventional methods are progressively insufficient to predict the safety of overall systems characterized by complex subsystem coupling, resulting from empirical and qualitative. Therefore, an innovative analysis that could quantify system safety with a standardized analysis accounting for the influence of multidimensional indexes that characterize different subsystems is proposed in this study. Specifically, an aviation piston engine is analyzed in this study as an illustration of the complex system. Firstly, a nominal model considering multiple subsystems of aviation piston engines is developed. Then, the indexes adopted to characterize the safety of the overall engine are obtained by injecting possible faults into the nominal model. Finally, a PCA-BPNN model is constructed to downscale the indexes and predict the safety rating. The application of the method to a total of 13 states containing normal and fault in the engine shows that the states ranking based on different indexes is varied as influenced by coupling. However, the ranking of states is consistent by PCA, proving the synthesis and rationalization of the analysis based on a multidimensional perspective. Specifically, the ranking of states from highest to lowest of severity is S 5 > S 7 > S 4 > S 6 > S 11 > S 3 > S 10 > S 9 > S 13 > S 2 > S 8 > S 12 > S 1 , where S 1 represents the normal state. Moreover, the predictive goodness of fit of the safety prediction model PCA-BPNN incorporating severity and probability achieves 0.986, which not only improves the efficiency but also avoids the impact of multiple covariances on the model performance. Results of the quantitative classification of safety rating for the case show that the inlet valve opening angle parameter has the highest safety rating 11, followed by the exhaust valve opening angle with safety rating 8. Therefore, a detailed safety analysis and design of the valve opening angle parameter is required, especially for the intake valve. Generally, the proposed method could provide additional clarification to the traditional local perspective analysis by considering the coupling, thus guiding the improvement from a safety aspect. [ABSTRACT FROM AUTHOR]

• Theoretical model for MF-PV2S aircraft engine gas exchange is established. • Prediction discrepancies of previous models are analyzed. • Modifying model zones and coefficients improve prediction accuracy. • Adaptability to varying conditions of speed, pressure, valve overlap, fuel type. • Model accuracy is validated by tracer gas method experiments. Under the demand of global aviation carbon reduction, the multi-fuel poppet valves two-stroke (MF-PV2S) aircraft engine exhibits advantages such as lower lubricant consumption and the flexibility to high-altitude valve timing adjustment, which position it to play a more significant role in general aviation aircraft and unmanned aerial vehicle propulsion systems. High-altitude gas exchange performance is a critical factor in the thermal efficiency and power characteristics of two-stroke aircraft engines. However, the applicability and accuracy of existing models in predicting the gas exchange process for PV2S engines remain insufficiently discussed. Recognizing discrepancies in the predictions of PV2S gas exchange processes by existing models, a theoretical model applicable to high-altitude gas exchange in an MF-PV2S aircraft engine is established. The modified model adjusts the exhaust composition during the second and third phases of the scavenging process, and a novel model characteristic coefficient, designated as b 3 , is incorporated to signify the proportion of mixed gas in the exhaust gases at a given moment. Moreover, the model characteristic coefficients b 1 and b 2 , are determined with nonlinearity, based on appropriate relationships that account for the characteristics of the PV2S gas exchange process. The model calculates gas exchange characteristics under different operating conditions and fuels, comparing these results with simulations and tracer gas-based experiments. The findings demonstrate that the model successfully captures the characteristics of early appearance and prolonged duration of fresh charge loss during PV2S gas exchange, significantly enhancing the predictive accuracy. Through adjustments of model coefficients based on specific conditions, the model predicts and describes the variation process of PV2S gas exchange performance parameters under different conditions, including various speeds, different intake-exhaust pressure differences at different altitudes, valve overlaps, and fuel types. The maximum relative errors between model predictions and experimental trapping efficiency, delivery ratio and charging efficiency are 2.58 %, 4.33 %, and 3.89 % respectively. The model can be used for rapid and accurate prediction of gas exchange characteristics under different conditions for the MF-PV2S aircraft engine. Also, it serves as an alternative model of three-dimensional simulation models that can be coupled into the one-dimensional thermodynamic cycle simulation. [ABSTRACT FROM AUTHOR]

This paper investigates the effects of soot inception and condensation polycyclic aromatic hydrocarbon (PAH) species and fuel preheating on soot prediction in 2D coflow laminar CH 4 /air diffusion flames doped with vaporized gasoline surrogate fuels, i.e., n- heptane/toluene mixtures. To evaluate the importance of considering multiple PAHs in soot inception and condensation and fuel pyrolysis near fuel tube outlet in the prediction of soot distribution along the flame centerline, the pyrene-based soot inception and PAH condensation model was improved by considering multi-PAH (A 2 , A 2 R 5 , A 3 C 2 H, A 4 , BGHIF) as nucleation and condensation species. The fuel preheating effect upstream the fuel tube exit was taken into account. Inclusion of multiple PAHs in soot inception and condensation leads to greatly enhanced soot formation along the flame centerline region due to enhanced soot inception and surface growth via PAH condensation. As a result of soot inception through smaller PAH (A 2), soot appears at a lower flame height above the burner exit than experiments. The fuel preheating effect causes significantly higher fuel stream temperatures in the near burner wall region and appreciable fuel pyrolysis. Soot inception is further enhanced by the fuel preheating effect and soot appears at an even lower height above the burner exit with a reduced flame height. This study demonstrated that both multi-PAH coagulation and fuel preheating strengthen soot inception and improve the predicted soot volume fractions along the flame centerline, but they are still insufficient to achieve good agreement with available experiments. Plausible ways to further improve the soot model are discussed. [ABSTRACT FROM AUTHOR]

• A dynamic safety assessment based on complex multi-physical model of aviation piston engine is proposed. • Quantifies the coupling between components from safety perspective of entire-engine model than qualitative analyzing single component. • The probabilistic effect of random failure time and random successive failure states of different components on the safety of entire-engine are the key technologies. • The method can accurately discriminate the coupled failure of different components in their respective safety range. Aviation piston engines constitute an essential segment of general aviation, whilst safety issues are becoming increasingly prominent by high system complexity. However, the conventional methods are gradually becoming insufficient to support the safety analysis in complex systems with multi-physical during the lifetime. Therefore, an innovative analysis that can depict the dynamic safety and potential coupled faults of the entire engine with multi-physical systems considering the effects of hybrid uncertainty faults is proposed in this study. Consequently, safety feedback is provided to the design in a more timely, accurate, and efficient manner based on the safety distribution throughout the lifecycle during the design stage. The analysis involves an integration of the nominal physical model and stochastic fault model via functionalized process variables. Firstly, a deterministic nominal model of the multi-physical domain of the engine is developed to characterize the coupled relationship between different domains by differential equations. Secondly, a stochastic fault model with hybrid uncertainty is quantitatively integrated into the nominal model for safety analysis by affecting process variables. Specifically, hybrid uncertainty encompasses the uncertainty of occurrence and severity. Finally, a simplified dynamic safety variation of the entire-engine is investigated by the approach. Result of Monte Carlo simulations of safety highlighted the coupled failures of different components in the respective safety ranges could be discriminated from the entire-engine perspective. The identification of potential coupled faults demonstrates the effectiveness and advantages of the proposed method in the design stage. [ABSTRACT FROM AUTHOR]

In the two-dimensional heat transfer experiments of aero-engine rotating disk cavities, the inverse heat transfer problem method can be used to obtain the wall heat flux numerically, which uses the two-dimensional measured wall temperature to solve the rotating disk heat conduction equation. A back propagation (BP) neural network data approximation method is proposed to reduce the ill-posedness of the two-dimensional inverse heat transfer problems in rotating disk cavities in this paper. The priori knowledge of wall temperature characteristics expressed by two-dimensional wall temperature first-order radial partial derivative distribution is used for BP neural networks' regularization. The distribution characteristics of the wall temperature first-order radial partial derivative in a typical preswirl rotating disk cavity were investigated by the flow-thermal coupling numerical simulation. Based on these characteristics, the BP neural network construction and training method with uncertain regularization coefficient is adopted. The numerical experiment results show that compared with the traditional polynomial fitting methods, the BP neural network approximation methods in this paper show significant advantages in data processing performance and stability; The fluctuation amplitude of the wall heat flux relative error on the disk surface can be reduced by 1–3 orders of magnitude, reducing the relative error of wall heat flux in most areas of the disk to within 20 % of the original value; The maximum wall heat flux relative error suppression area where | δq r ,cal / δq r ,mea × 100 %| < 100 % of BP neural network approximation method can reach 1.93 times that of the traditional fitting method, and 3.18 times for the area where | δq r ,cal / δq r ,mea × 100 %| < 30 % in the current study. • Wall temperature first-order radial partial derivative priori knowledge is used for BP neural network regularization. • The construction and training method of BP neural network with uncertain regularization coefficient is proposed. • The two-dimensional heat flux relative error fluctuation amplitude can be reduced by 1–3 orders of magnitude. • BP neural network shows significant advantages in data processing effect and stability compared with polynomial fitting. [ABSTRACT FROM AUTHOR]

Safety analysis of complex systems, such as aero-engines, has always been a challenging problem. In particular, the risk propagation caused by system functional interactions has become increasingly prominent, leading to the difficulty of traditional safety analysis methods. Existing methods are mostly based on manual experience and deduction with difficulty to completely analyze the whole system safety regions. In this paper, a model-based framework is proposed by combining Finite State Machine Network (FSMN) and phase space theory to perform safety analysis of complex systems from function-logic perspective. We first construct the system model and system state-transition network based on FSMN. Then combining with phase space theory, we identify system safety regions of the entire operating space from macro perspective, and investigate the system risk propagation from micro perspective. An aero-engine system is taken as an example to illustrate the proposed method. Our results show that this method has the ability to effectively identify the potential risk factors and explore emergent unknown risks, which can provide guidance for safety testing. [ABSTRACT FROM AUTHOR]

Probabilistic damage tolerance assessment is an essential method to evaluate the safety of aeroengine rotors. The stress intensity factors (SIFs) are the core parameters. The weight function method can calculate SIF efficiently. The available weight functions for corner cracks are suitable for cracks with universal stresses. However, when cracks are under bivariant stress distributions, the lack of the weight function database makes the damage tolerance assessment impractical. Therefore, this paper derives the point weight functions for corner cracks, which are suited for cracks in real-world components with two-directional stress distributions. The response surface method is used to build the surrogate model of the point weight functions. By integrating the weight functions with the stress distributions, SIFs can be calculated with high accuracy. In sum, 81% of the differences between the point weight function method and finite element results are less than 10%. [ABSTRACT FROM AUTHOR]

Limited miscibility may be a major concern for the use of ethanol in jet fuels particularly when water is present. Herein miscibility data were obtained for mixtures composed of a kerosene-based surrogate fuel (80% n-decane and 20% 1,2,4-trimethylbenzene by mass), ethanol and water in varying percentages at −1.7 °C, 11.4 °C, 25 °C and 66 °C. The results indicated that the purity requirement of hydrous ethanol increased with the surrogate fuel percentage. The purity requirement increased when the temperature decreased. The upper limit for water tolerance was largely above the azeotropic value (4.4% water content) at 25 °C and 66 °C, which indicated that the blends can be miscible at room temperature and above even though water content is higher than the azeotrope concentration. In addition, emulsifier, in the low percent range (below 2% by volume), was shown to have notable effects on the phase behavior of the ternary mixtures. Liquid–liquid equilibrium (LLE) experimental data at 101.32 kPa were compared with simulation results by means of the UNIFAC-LLE model, which provided satisfactory results with moderate deviation from experimental data. A Matlab-based program was developed to determine the compositions of individual phases for any initial mixtures with known compositions. [ABSTRACT FROM AUTHOR]

• Combustion systems and aviation adaptability in piston engines are analyzed. • The key technologies related to in-cylinder combustion research are summarized. • Combustion characteristics and aviation adaptability of fuels are examined. • Future development directions of combustion technology are analyzed and predicted. The in-cylinder combustion process is a focus on research on heavy fuel aviation piston engine (HF-APE), which is quite significant because of its strong correction with engine's power and economic performance, as well as the level of emissions. This study reviews the representative combustion types of HF-APE in recent years, and comprehensively analyzes their aviation adaptability from various aspects. A review was conducted from the perspective of visualization measurement, combustion analysis, and high-altitude simulation technologies, all of which are the crucial methods to study the HF-APE combustion process. A comparative study was investigated on the combustion characteristics and aviation adaptability under different fuels. To meet the requirements of airworthiness regulations and the development of general aviation for more energy saving and environmental protection, further summarizing the progress as well as predicting the trends of HF-APE combustion technologies, are expected to be promoted due to their valuable scientific significance and engineering applications. [ABSTRACT FROM AUTHOR]

Hydrogen propulsion is generally treated as the ultimate net zero-emission option for aviation, therein liquid hydrogen storage appears to provide the only feasible solution for aircraft with the constraints imposed by aircraft weight and volume. Hydrogen liquefaction consumes a great amount of energy, which significantly boosts the cost of hydrogen as an aviation fuel. Besides the H 2 chemical exergy for combustion to provide thrust, the H 2 physical exergy in the form of cold energy is also a kind of high-quality clean energy to produce power output, which offers great opportunities to achieve cost-effective use of hydrogen fuel. Thus, this paper presents a Rankine cycle and H 2 direct expansion cycle (RC-DEC) combined power generation thermal management system for the simultaneous utilization of exhaust gas heat exergy and hydrogen fuel cold exergy from the liquid hydrogen-fueled turbojet engine. In the Rankine cycle, the transcritical mode is applied on the hot side while the liquid separation condensation concept is adopted on the cold side to achieve better thermal matchings with heat and cold sources. The hydrocarbon/inert gas binary mixture is proposed as the working fluid of the Rankine cycle. The effects of key thermodynamic parameters and the influence of Para-Ortho hydrogen conversion on system performance are discussed, then a comparison of the mixture working fluid is conducted. Results show that there exists an optimal separation temperature ratio and condensation pressure of RC to obtain maximum total net power output. As the DEC expander inlet pressure increases, the total net power output first increases and then levels off. The introduction of the Para-Ortho hydrogen conversion has a negligible impact on net power output but leads to a significant reduction in the exergy efficiency, which is attributed to the cold energy release nature of Para-Ortho hydrogen conversion. The results of the working fluid comparison indicate that the optimal inert gas retardant for CH 4 is Kr, while those for C 2 H 6 and C 3 H 8 are Xe to achieve the maximum net power output and exergy efficiency of the proposed power generation system. Among them, C 2 H 6 /Xe(0.6/0.4) obtains the maximum net power output of 2717.9 kW and maximum exergy efficiency of 33.1%, which suggests an opportunity to provide megawatts of electrical power for the aircraft in place of the APU. • RC-DEC combined thermal management system is proposed for LH 2 turbojet engine. • The hydrocarbon/inert gas binary mixture is proposed for LH 2 cold exergy recovery. • The influence of the Para-Ortho hydrogen conversion on the system is revealed. • The optimal inert gas retardant for the selected hydrocarbons is determined. [ABSTRACT FROM AUTHOR]

Bump foil journal bearings (BFJBs) are widely used in the superchargers of aviation piston engines (APEs). This paper proposes a method to evaluate the operating state of superchargers by monitoring the bearing temperature. A numerical model with a repeating symmetrical structure in the axial direction is established based on a certain type of supercharger, which solves the temperature field of BFJBs with the non-isothermal Reynolds equation and energy equation. It can be used to analyze the effect of thermal expansion on lift-off speed and stop-contact speed. A new test rig and six various BFJBs were designed to check the temperature characteristics of the BFJBs with variable load and speed. By comparing the numerical results with the experimental results, it was shown that the air film temperature increased almost linearly with the increase in bearing load and speed. However, the temperature increase caused by the rotation speed was significantly greater than the load. The structural parameters of the BFJB affected the bearing support stiffness, which had a nonlinear effect on the lift-off speed and air film temperature. Therefore, the proposed method to evaluate the state of superchargers with BFJBs was effective. These thermal characteristics can be used to guide BFJB design and predict the life cycle of BFJBs. [ABSTRACT FROM AUTHOR]

Abstract: Dynamic systems with stochastic input processes are general engineering models. In order to apply the global sensitivity analysis on these systems to aid safety design, variance based sensitivity indices are extended to stochastic processes in this paper. Factor sensitivity indices and time sensitivity indices are defined to describe the contributions of the input factor variances of the whole time and a specific time to the output variance at the current time, respectively. Analytical expressions of sensitivity indices for linear time-invariant systems with Gaussian processes are derived due to the extensive use of them, including continuous-time systems and discrete-time systems. Monte Carlo simulation is used to verify the derived analytical expressions. The derived expressions could be used directly in practical applications to reduce computation cost. The applications of the sensitivity indices have been discussed with engineering examples, which include transient temperature measurements and a forced vibration system. Some safety design measures aided by the sensitivity indices are also discussed in these two examples. [Copyright &y& Elsevier]

Abstract: The suitability of three different two-equation turbulence models in predicting film cooling effectiveness on a rotating blade was investigated and they are the commonly used standard k-ε model, the k-ω model and the shear stress transport k-ω model. To fulfill this target, both numerical simulation and the experimental investigation were carried out for a rotating blade having a flat test surface with a 4mm diameter straight circular cooling hole in 30° inclined injection. The blade rotated at five different speeds of 0, 300, 500, 800 and 1000rpm. The momentum ratio was set to be 0.285 and the Reynolds (Re D) number based on the mainstream velocity and hydraulic diameter of the mainstream channel is 1.45×105. The averaged density ratio was chosen to be 1.026 with air as both the coolant and the mainstream. Comparison between the numerical work and the experimental results indicated that (1) the rotating speed is the most critical parameter influencing the film cooling effectiveness distributions and the pressure surface could be remarkably different from the suction surface, (2) as for the algebraic averaged film cooling effectiveness, numerical predictions of the three turbulence models all overshoot compared with the experimental results, (3) among the three turbulence models, the standard k-ε model gave the poorest prediction. [Copyright &y& Elsevier]

Abstract: A new rotating test rig was set up to investigate the rotation effect on the film cooling over the flat wall. A simple flat blade with an inclined 30° film hole, which is parallel to the hot mainstream, was installed. And different rotation orientations were selected to simulate the blade pressure or suction side of a turbine blade. A steady liquid crystal technique was applied to obtain detailed distribution of the temperature over the blade surface. And the average adiabatic film cooling effectiveness of the area adjacent to the film hole was selected to evaluate the cooling effect. Five different rotational speeds, i.e., 0, 300, 500, 800, 1000r/min, were considered. Experimental results indicate that the film trajectory could bend under the rotating condition. With the increase of the rotational speed, on the pressure side, the film trajectory inclines centripetally firstly and then centrifugally; whereas, on the suction side the film trajectory bends centrifugally. On the other hand, as the rotational speed increases, the cooling effect is improved firstly and then worsened when Ω >500–600r/min on the pressure side. On the suction side, however, the cooling effect is not sensitive to the rotational speed. [Copyright &y& Elsevier]

Abstract: In the cavity between the co-rotating compressor discs in gas turbine engines, the flow is very complex because of the multiple driving forces including the centrifugal buoyancy force, the Coriolis force and the inertial force. Numerical analysis was carried out in a simple rotating cavity with cooling air axial throughflow and a heated shroud. Efforts were focused upon the flow structure and its variations. The results reveal the non-axisymmetrical flow structures with cyclonic and anti-cyclonic circulations, which slip relative to the rotating cavity in the opposite direction (that is, rotate with a slower speed than the cavity) and the patterns remain unchanged. These structures are not unique, and four types with one, two, three, four pairs of circulations are obtained. For any particular set of conditions, the final structure can depend on the path taken: as axial Reynolds number is increased the number of circulation couples increases, and as Grashof number is increased the number of circulation couples decreases. At high Grashof number, the variation of Nu av with Gr is consistent with the Rayleigh–Bénard convection. [Copyright &y& Elsevier]

• Neural network regularization is completed using wall temperature first-order derivative as prior knowledge to reduce the ill-posedness of inverse heat transfer problem. • The RBF + BP approximation method with uncertain regularization coefficient is proposed. • The heat flux relative error can be reduced by 1 ∼ 2 orders of magnitude compared with several traditional data fitting methods. • The demand for measurement points can be reduced by approximately 44 ∼ 60 % compared with Bayesian inference method. Solving the heat conduction equation using surface measurement temperature as boundary conditions to obtain surface heat flux is an ill-posed inverse heat transfer problem, in which small temperature errors can create large uncertainties in heat flux. This paper proposes a RBF (Radial Basis Function) + BP (Back Propagation) neural network approximation method that uses the wall temperature characteristics as priori knowledge to reduce the ill-posedness of the inverse heat transfer problem in rotating disc cavities of aero-engines. The wall temperature characteristics are described using first-order derivative, which are discussed and obtained through analytical solution and fluid-thermal coupling numerical simulation. Bayesian inference theory is used to construct neural network training objective function with regularization term and the RBF + BP neural network approximation method with uncertain regularization coefficient is proposed. Numerical experiments were conducted based on numerical simulation data to verify the effectiveness of the proposed method. The results show that the method can effectively suppress the ill-posed nature of the inverse heat transfer problem and can reduce the heat flux relative error level by 1 ∼ 2 orders of magnitude compared with several traditional data fitting methods commonly used in rotating disc cavities. The method of densifying measurement points combined with priori knowledge revision near the air impact point can effectively capture the local heat flux characteristics caused by airflow impact. The RBF + BP approximation method can reduce the demand for measurement points by approximately 44 ∼ 60 % under the error of 3 σ = 0 K ∼ 0.9 K compared with Bayesian inference method. [ABSTRACT FROM AUTHOR]

Radial compressor impeller (RCI) manufacturing is moving toward to improve competitiveness through smart manufacturing. Although current CAD (computer-aided design) and CAM (computer-aided manufacturing) techniques provide multiple tools to construct and optimize complicated geometries of RCI, an adjustment of blade shape often leads to nonparametric geometric reconstruction. As the key geometric elements in RCI, set of streamlines (SSL) and meridional section (MS) play vital roles in modeling and aerodynamic optimization. This paper presents a novel approach for automatic extraction of SSL and MS from a RCI 3D model or workpiece. Furthermore, the presented method can interactively construct a parameterized RCI platform, which inputs and outputs the presented RCI parameters to existing CFD and CAM systems rapidly and effectively. An integrated acquisition is employed. The straight generatrix vectors (SGVs) are identified and their boundary points are defined. After the uniform partition of SGV segments, the sequent equant points along spanwise direction are packaged to fit SSL. To manipulate the smoothness and approximation, a double-fitting method is performed to generate SSL. A parameterized system for extracting SSL and modeling RCI is developed. The validities of the presented method in different systems are demonstrated. Furthermore, the presented method breaks conventional RCI development procedure and shortens RCI product cycles, which is desirable and significative for integrated RCI design and manufacturing. [ABSTRACT FROM AUTHOR]

• High-altitude performance of poppet valves 2-stroke engine is studied. • Reformative test platform and simulation model predict the performance accurately. • Tracer gas method and mass flow acquisition method are feasible at high altitudes. • High-altitude power deterioration is more severe than conventional 2-stroke engine. • Two effective performance improvement methods for high altitudes are proposed. Poppet valves 2-stroke (PV2S) diesel engine is promising to overcome the problems of low combustion performance and deteriorated emissions of conventional 2-stroke aircraft engines due to the lubricant leakage into cylinders. However, the high-altitude gas exchange and power performance of PV2S diesel engine with complex supercharging systems have been rarely studied, and the corresponding experimental methods are expected to be improved. To address these issues, a reformative experimental platform and one-dimensional simulation model are proposed to accurately predict the high-altitude performance and explore the improvement methods of a PV2S aircraft diesel engine with a combined supercharging system. Tracer gas method and pressure-based mass flow acquisition method are innovatively conducted in the platform to measure the gas exchange characteristics, which are validated with satisfactory accuracy and feasibility. The results indicate the performance deterioration of the PV2S engine is more severe than conventional 2-stroke engines due to the additional decrease of trapping efficiency. As the altitude increases from sea level to 8000 m, delivery ratio, trapping efficiency, charging efficiency and available brake power decrease by 22%, 27%, 43% and 61% respectively. Adjustments of valve overlap duration, as well as exhaust manifold length and chamber volume, can effectively improve the charging efficiency and brake power, which increase by 36.73% and 30.38% at 8000 m altitude, whereas at sea level they decrease 5.68% and 8.39% respectively. The study reveals the feasible application of PV2S diesel engine in aircraft propulsion and facilitates its use at high altitudes. [ABSTRACT FROM AUTHOR]

Highlights • Thermal loading rapid variation causes the dangerous transient process for aeroengines. • The essence of thermal loading control in key disk is a process of thermal management. • Stress level can be ameliorated by actively adjusting the thermal management strategy. • The artificial opposite thermal stress counteracts part of the centrifugal stress. • The DIC-2D system can accurately measure the in-plane thermal-structure deformation. Abstract The use of either the passive or active types of thermal loading management, which are realised by the thermal protection and thermal loading reorganization, respectively, is determined by the thermal management strategy. Therefore, this study investigates and assesses the thermal stress evolution characteristics and their resulting effects on an aeroengine disk under different thermal loading management strategies. The non-contact rotational deformation measurement system based on the DIC-2D technology is used to measure the in-plane thermal-structure deformation and the transferred stress on a high-speed rotating disk. Three levels of heating power for the outer and inner heating coils are used to apply the thermal loading conditions for the considered thermal management tests. The results show that the equivalent stress level is decreased by 14.29% and that the safety margin is increased by 23% in the transient process under the active thermal loading management strategy conditions at Te e = Level 2 and Te i = Level 3. Compared with the passive thermal loading management strategy, the physical explanation for the above-mentioned results is that the direction of the actively built thermal stress between the web and hub of the disk is opposite to that of the centrifugal stress due to the additional heating energy present in the active thermal management strategy. Thus, part of the centrifugal stress is counteracted. The results of the analysis performed using the non-dimensional universal thermal management theoretical models are consistent with the experimental results. [ABSTRACT FROM AUTHOR]

Highlights • A small-scale waste heat recovery system by virtue of Tesla turbine is proposed. • Computational fluid dynamics simulations on Tesla turbine are performed to calculate flow and pressure field. • A performance experiment of Tesla turbine is conducted to validate simulation results. • Tesla turbine clearly improves total power and thermal efficiency over a low rotation-speed range. • Working-fluid property and number of nozzles impact Tesla turbine performance. Abstract Waste heat recovery is significant to improve energy utilization. Expander is one of the most important components in waste heat recovery. Tesla turbine offers an attractive option for the expander if an efficient design can be well achieved. Faced the theoretical and computational challenges associated with the feasibility of Tesla turbine in a small-scale waste heat recovery system, this paper formulates a systematic design methodology to seek optimal parameters and geometric model of the Tesla turbine which is applied to a coolant waste heat recovery system of an automobile engine. To achieve this goal, a detailed investigation into the performance of Tesla turbine, which incorporates experimental and computational fluid dynamics analysis manifests that Tesla turbine achieves higher performance at lower rotation-speed. Performance analysis on the waste heat recovery system under various operating conditions is conducted based on a comprehensive thermodynamic model. Results show that the total power and overall thermal efficiency of the waste heat recovery system are clearly increased over a low rotation-speed range, furtherly, which can be improved by selecting appropriate viscosity of the working fluid and number of nozzles. It is desirable and significative to effectively improve power output and thermal efficiency for an automobile engine at a lower expense of volume and cost. [ABSTRACT FROM AUTHOR]

Abstract Ignition delay times for 1,3-butadiene oxidation were measured in five different shock tubes and in a rapid compression machine (RCM) at thermodynamic conditions relevant to practical combustors. The ignition delay times were measured at equivalence ratios of 0.5, 1.0, and 2.0 in 'air' at pressures of 10, 20 and 40 atm in both the shock tubes and in the RCM. Additional measurements were made at equivalence ratios of 0.3, 0.5, 1.0 and 2.0 in argon, at pressures of 1, 2 and 4 atm in a number of different shock tubes. Laminar flame speeds were measured at unburnt temperatures of 295 K, 359 K and 399 K at atmospheric pressure in the equivalence ratio range of 0.6–1.7, and at a pressure of 5 atm at equivalence ratios in the range 0.6–1.4. These experimental data were then used as validation targets for a newly developed detailed chemical kinetic mechanism for 1,3-butadiene oxidation. A detailed chemical kinetic mechanism (AramcoMech 3.0) has been developed to describe the combustion of 1,3-butadiene and is validated by a comparison of simulation results to the new experimental measurements. Important reaction classes highlighted via sensitivity analyses at different temperatures include: (a) ȮH radical addition to the double bonds on 1,3-butadiene and their subsequent reactions. The branching ratio for addition to the terminal and central double bonds is important in determining the reactivity at low-temperatures. The alcohol-alkene radical adducts that are subsequently formed can either react with HȮ 2 radicals in the case of the resonantly stabilized radicals or O 2 for other radicals. (b) HȮ 2 radical addition to the double bonds in 1,3-butadiene and their subsequent reactions. This reaction class is very important in determining the fuel reactivity at low and intermediate temperatures (600–900 K). Four possible addition reactions have been considered. (c) 3Ö atom addition to the double bonds in 1,3-butadiene is very important in determining fuel reactivity at intermediate to high temperatures (> 800 K). In this reaction class, the formation of two stable molecules, namely CH 2 O + allene, inhibits reactivity whereas the formation of two radicals, namely Ċ 2 H 3 and ĊH 2 CHO, promotes reactivity. (d) Ḣ atom addition to the double bonds in 1,3-butadiene is very important in the prediction of laminar flame speeds. The formation of ethylene and a vinyl radical promotes reactivity and it is competitive with H-atom abstraction by Ḣ atoms from 1,3-butadiene to form the resonantly stabilized Ċ 4 H 5 -i radical and H 2 which inhibits reactivity. Ab initio chemical kinetics calculations were carried out to determine the thermochemistry properties and rate constants for some of the important species and reactions involved in the model development. The present model is a decent first model that captures most of the high-temperature IDTs and flame speeds quite well, but there is room for considerable improvement especially for the lower temperature chemistry before a robust model is developed. [ABSTRACT FROM AUTHOR]

Considering that either passive thermal management from thermal protection or active thermal management from thermal loading reorganization is determined by thermal management strategy, this paper proposes an evaluation method based on the zoning of the stress states of a disk for different thermal management strategies to assess the advantages and disadvantages of different thermal loading combinations or distributions at the initial design stage. The theoretical model for thermal management strategies is first established by abstracting the combination of thermal loading parameters ( Q e , Q in and h ¯ ). Subsequently, the zoning principles are defined based on the stress state characteristics. The sensitivity factors S σ , in and S σ , e are introduced to quantify the variation degrees of the thermal loading parameters Q in and Q e for stress state. A rotating turbine disk with a nearly real geometry is used as evaluation object to investigate the effects of different thermal management strategies from three aspects: the position of maximum stress, the iso-surface of the maximum stress level and the variation profile of the disk. Results show that the stress states for each thermal management strategy can be divided into four zones based on the position of the maximum von-Mises stress and the direction of the circumferential stress. A three-dimensional space region partition is generated for each stress state, which shows that the appropriate thermal loading combinations in the design are limited and have an application scope. Generally, the thermal loading combinations in the Domain 1(I) zone represent the most appropriate objects in the design process, whereas the other zones should be avoided because of the enormous negative temperature gradient they produce in the disk. Moreover, the values of sensitivity factors S σ , in and S σ , e in the considered disk profiles are similar, and the effects of the variations in the thermal loading parameters Q in and Q e on the maximum stress are not influenced by the disk profile. [ABSTRACT FROM AUTHOR]

Using the Thermochromic Liquid Crystal (TLC) technique, one downstream sister holes and one base round hole were investigated experimentally to study the effect of rotation on film cooling performance on a flat plate test model. Blowing ratios of 0.3, 0.5, 1.0, 1.5, 2.0 and 2.5 were studied. Density ratio of the cooling air to hot air was 1.05. The mainstream Reynolds number (Re D ) was 3400, and 4 rotation speeds of 200, 400, 600 and 800 rpm were applied on both the pressure side (PS) and suction side (SS). Under rotation, the film cooling performance of the downstream sister holes improved clearly at blowing ratio M = 0.3–2.5, both on the PS and SS. For both the base hole and downstream sister holes, the film trajectory showed a distinct centrifugal deflection on the SS, with lower film cooling effectiveness than that on the PS. On the PS, the rotation number had a clear effect on film cooling performance, which increased first and then decreased with increased rotation speeds and reached the highest value at 600 rpm. [ABSTRACT FROM AUTHOR]

A conjugate heat and mass transfer model was developed for microwave freeze drying within porous media with dielectric cores. The set of transient governing equations developed was solved numerically using finite volume method with variable time-steps. Analysis of numerical results may lead to following main conclusions: (1) by carefully choosing the loss factor and size of the dielectric cores could dramatically reduce the drying time, (2) the size and the loss factor &epsiv;″ of the dielectric core are the two important parameters influencing the drying process, (3) there may be two sublimation fronts in existence within the porous media. [Copyright &y& Elsevier]

• A novel BTC measurement method based on event capture technique is proposed. • BTC values are solved based on the relationship between the counts of events and BTC distribution. • Accuracy, sensitivity, range and stability are demonstrated by the relationship equations. • A test to validate the proposed method in BTC measurement for a turboengine is performed. • Comparing with continuous sampling method, the measurement error is within 0.01 mm, and hardware occupation is reduced to 0.1%. Blade tip clearance (BTC) measurement is an essential technology in turbomachinery health monitoring so as to enhance efficiency and reliability as well as to ensure timely maintenance. The existing BTC measurement methods, which based on continuous sampling technique, depend highly on the devices sampling frequency, data transmission speed, storage memory, and computation capability, can hardly achieve online real-time measurement and long-term continuous monitoring. BTC distribution of a turbomachinery possesses discreteness, symmetry, monotonicity and quasi-periodicity, based on these characteristics, this paper proposes a novel BTC measurement method based on event capture technique. The method sorts the sensors signal into distinct events according to pre-set trigger thresholds, describes the relationship between the event kinds and the BTC distribution via mathematical equations, and solves the BTC values accordingly. The measurement error, measuring sensitivity, measurable range, and solving stability of the proposed method are demonstrated. A test to validate the proposed method for BTC measurement in the inlet section of a turboengine is performed, and the results show that, the event capture technique is capable of achieving fast and accurate BTC measurement. The proposed methods own a measurement error within 0.02 mm (for dual-channel configuration) and 0.01 mm (for multi-channel configuration) comparing with the continuous sampling technique. Meanwhile their hardware resource requirement are reduced to 0.02% (for dual-channel configuration) and 0.1% (for multi-channel configuration) comparing with the continuous sampling technique. For processing these performances, the proposed method can be applied for online real-time BTC measurement and long-term continuous BTC monitoring. [ABSTRACT FROM AUTHOR]

Blade tip clearance (BTC) measurement and active clearance control (ACC) are becoming crucial technologies in aero-engine health monitoring so as to improve the efficiency and reliability as well as to ensure timely maintenance. Eddy current sensor (ECS) offers an attractive option for BTC measurement due to its robustness, whereas current approaches have not considered two issues sufficiently. One is that BTC affects the response time of a measurement loop, the other is that ECS signal decays with increasing speed. This paper proposes a speed adjustment model (SAM) to deal with these issues in detail. SAM is trained using a nonlinear regression method from a dynamic training data set obtained by an experiment. The Levenberg–Marquardt (LM) algorithm is used to estimate SAM characteristic parameters. The quantitative relationship between the response time of ECS measurement loop and BTC, as well as the output signal and speed are obtained. A BTC measurement method (BTCMM) based on the SAM is proposed and a geometric constraint equation is constructed to assess the accuracy of BTC measurement. Experiment on a real-time BTC measurement during the running process for a micro turbojet engine is conducted to validate the BTCMM. It is desirable and significative to effectively improve BTC measurement accuracy and expand the range of applicable engine speed. [ABSTRACT FROM AUTHOR]