Performance Of Aero-engine Research Articles

Numerical Investigation on the Influence of Continuous Rotating Backpropagation Pressure Wave on Turbine Performance

Abstract Researches have shown that the use of a continuous detonation afterburner can improve the propulsion performance of aero engine. However, backpropagation pressure waves (BPW) generated by the pressure gain of detonation will affect the internal flow and performance of turbine. This article simulates BPW through a custom function, and investigates the effects of BPW amplitude, rotation frequency, and propagation mode on turbine performance through three-dimensional simulation. The results show that as the pressure amplitude of the BPW increases, the pressure oscillation at each section of the turbine increases and a local subcritical flow state will appear, leading to the decrease of turbine flowrate and turbine power, as well as an intensification of instantaneous turbine power fluctuations. As the rotation frequency of the BPW increases, the pressure oscillation at each section of the turbine gradually decreases. The flowrate and power of the turbine do not change much, but turbine efficiency gradually decreases. Compared to the aligned mode, the turbine performs better under the influence of BPW in misaligned mode. Compared to the single-wave mode, the fluctuation of transient turbine power is lower under the influence of BPW in the multiwave mode excluding collision mode. Finally, the constraints of equal flowrate region and equal turbine power line on the peak-to-peak value of the BPW were analyzed when the joint operation of the turbine and compressor was not affected. The rotation frequency and mode of BPW will affect the flowrate region and power line.

Design and implementation for the state time-delay and input saturation compensator of gas turbine aero-engine control system

In order to obtain desired steady-state and transient performance of a gas turbine aero-engine during its operation, a usual way is to control the engine to operate in a manner close to its physical limits. The thermodynamic performance of a gas turbine aero-engine varies greatly within a wide working envelope, affected by factors such as engine performance degradation, actuator response lag and combustion time-delay. When the engine works in extreme conditions, for example rapid acceleration, some phenomena such as over-speed, over-temperature and over-pressure may occur. For this reason, various restrictions are often set in the engine control system to ensure safety during its operation, which are often realized by the form of saturation. In this paper, a compensation structure for gas turbine aero-engine state time-delay and input saturation is proposed. At first, the problems frequently occurred in the gas turbine aero-engine control system are investigated. And the gas turbine aero-engine control model is derived based on a thermodynamic non-linear model and its linearization model is established, together with its designed compensation structure. Differing from the existing technologies, a combination of dynamic system input saturation feedback and static state time-delay feedback is adopted in the proposed model. Then, the saturated nonlinearity and time-delay characteristic are introduced as convex combinations in the stability analysis. The local stability conditions of the closed-loop system are obtained by using Lyapunov–Krasovskii functionals and linear matrix inequalities (LMIs). Finally, hardware-in-loop (HIL) experiments are conducted to verify the feasibility of the proposed compensation method.

MSCNN-BLSTM based Prediction of the Remaining Useful Life of Aeroengine

Accurate prediction of the aeroengine remaining useful life (RUL) is essential to improve engine availability and reliability. Aiming at the reliable prediction of residual life of aeroengine system, an engine residual life prediction model based on the fusion of multiscale fusion two-dimensional convolutional neural network and bidirectional long and short term memory (MSCNN-BLSTM) is proposed. Based on the fusion of two-dimensional convolutional neural network and bidirectional long and short time memory (BLSTM) network, the engine medium and advanced features extracted by the convolutional neural network are integrated to make residual life prediction. Finally, C-MAPSS dataset provided by NASA was used for validation. It is shown that the proposed multiscale hybrid model, compared with other model predictions, reduces the performance index score and root mean square error by 32.2% and 14.7% respectively. It can be seen that the data-driven model can effectively extract the information from the degradation data, which improves the prediction performance of aeroengine remaining life.

Simulation Analysis and Process Evaluation of Cooling Hole Forming Precision in Mask Assisted Electrochemical Machining Based on GH4169.

Good heat dissipation performance of aero-engine an effectively improve the service performance and service life of aero-engine. Therefore, this paper studies the machining method of cooling holes of high-temperature existent material GH 4169 for aero-engine innovatively puts forward the mask electrochemical machining method of cooling holes and explores the entrance morphology and taper formation law of the hole structure of high-temperature resistant material GH 4169. The mathematical model of anode dissolution of cooling holes in ECM is established, and the influence of voltage and electrolyte flow rate on cooling holes in ECM is analyzed. Compared with the mask-less electrochemical machining, the inlet radius of cooling holes in mask electrochemical machining is reduced by about 16.0% and the taper is reduced by 52.8% under the same machining parameters, which indicates that the electrochemical machining efficiency of mask is higher and the machining accuracy is better. Experiments show that the diameter of the mask structure improves the accuracy of the inlet profile of the cooling hole in the ECM. The diameter of the mask increases from 2 mm to 2.8 mm, and the inlet radius of the cooling hole increased from 1.257 mm to 1.451 mm When the diameter of the mask is 2.2 mm, the taper of the cooling hole decreased by 53.4%. The improvement effect is best, and the thickness of the mask has little influence on the forming accuracy of the cooling hole.

Experimental study on the influence of airflow velocity on frosting and defrosting performance of compact precooler under actual air humidity condition

Due to the precooler of hypersonic vehicle is frosted during the process of operation, the flow channel is blocked and the performance of engine is affected, which resulting in the decline of thrust and specific impulse. Therefore, for the purpose of maintain the performance of aero-engine, it is necessary to defrost the precooler. In order to study the influence of the airflow velocity on the frosting and defrosting performance of the compact precooler under actual air humidity condition, the frosting and defrosting performance of the microtubule precooler are experimentally studied in the wind tunnel under the conditions of air humidity of 1.8 g/kg and main flow velocities are 10 m/s, 20 m/s and 30 m/s, respectively. Methanol is utilized as the defrosting solvent, the mass ratio of methanol ranges from 0.8 to 1.2. The experimental results reveal that under the frosting experimental conditions, frost layer quickly condenses on the outside of tube bank, the wall surface temperature and heat transfer rate decrease dramatically, but the pressure drop coefficient increases sharply. It indicates that the frosting has an adverse effect on throughflow characteristics and heat transfer performance of the precooler. However, for the defrosting experiments, the wall temperature increases significantly, the defrosting effect and heat transfer rate are improved obviously and the pressure loss coefficient drops distinctly. In addition, with the increase of airflow velocity, the pressure drop coefficient increases sharply, but the coverage area of the frost layer gradually decreases, it manifests that increasing the main flow velocity is beneficial to suppress the formation of the frost layer. Through the analysis of experimental results, it can be found that within the range of experimental study parameters, the optimal defrosting performance can be obtained when the mass ratio of methanol is about 1.1. Moreover, with the increase of mass ratio of methanol, although the amount of condensation decreases, the condensation gradually evolves from the fluffy frost layer to the mixture layer of frost and ice, and eventually develops to whole ice layer.

A neural network learning-based global optimization approach for aero-engine transient control schedule

Transient performance of aero-engine determines the maneuverability of aircraft. The optimal control schedule can tap the potential transient performance with subject to each constraint. Thus the transient time can be minimized with the optimal transient control schedule. This transient schedule is described by a strong constrained and nonlinear problem. It is therefore challenging to present an optimal method to achieve the best transient schedule. Motivated by solving this problem, a surrogate-assisted optimization framework is presented by using the learning capability of neural networks. It is achieved by presenting a sequential ensemble radial basis function (RBF) neural network-based optimization (SERO) algorithm. The advantage of the RBF neural network such as excellent prediction accuracy is taken and integrated into the surrogate-assisted optimization algorithm to improve the algorithm performance. With the application of the proposed scheme, the global optimization schedule is guaranteed for aero-engine transient control. Numerical validation is finally carried out by applying the presented optimization framework to a mixed-flow aero-engine transient control schedule. It is demonstrated that the SERO approach can minimize the transient process time despite any constraint at any time.

A New assembly precision prediction method of aeroengine high-pressure rotor system considering manufacturing error and deformation of parts

The accurate prediction of high-pressure rotor system assembly precision before assembly is the premise of improving aeroengine assembly quality and performance. The existing assembly precision prediction models (APPM) only consider the manufacturing error factors of parts, but rarely involve the deformation of parts under load, so there is a certain gap between the prediction results and the actual situation. This article studies the construction method of APPM considering the manufacturing error and deformation factors of parts. Firstly, the fitting algorithm is used to obtain the fitting deformation surface(FDS) of each mating surface under load, which provides the basis for constructing assembly error model considering manufacturing error and deformation of parts; secondly, according to the relative position relationship between the FDS and the datum plane, the error model of each mating surface of the assembly is effectively constructed by the small displacement torsor theory; thirdly, according to the different errors of each fitting end face, a prediction model of assembly precision for two rough surfaces is constructed by homogeneous coordinate transformation method; finally, a high-pressure compressor rotor system is used as an example to verify the effectiveness of the precision prediction model. The results show that the prediction results based on the proposed model are closer to the actual conditions. This paper provides an effective prediction model for high-pressure rotor system assembly precision, and has important application value for improving the assembly quality and performance of aeroengine.

Performance optimization scheme of turboshaft aeroengine based on Bayesian network

The turboshaft aeroengine is mainly used in helicopters. As a power device that drives the rotor to generate lift and propulsion, it has been rapidly developed in recent years. The manufacturing process of turboshaft aeroengine is complex, and there is a strict factory inspection mechanism. Only when the various performance indicators meet the qualified requirements of the factory conditions, it makes the ex factory pass rate of turboshaft aeroengine often not ideal. The key section temperature is an important indicator to characterize the performance of turboshaft aeroengine. In order to ensure the reliability of the whole machine, it has a maximum temperature limit. According to the manufacturer's suggestions, four attribute variables that affect the key section temperature are extracted to form a research data set. Then, after preprocessing the data set, the performance model for the turboshaft aeroengine is established based on the Bayesian network. According to the characteristics of Bayesian network, the posterior qualified probability is calculated through probabilistic reasoning of the performance model, and the current mainstream machine learning algorithms are introduced to compare and verify the validity of the performance model. Finally, the recommended state combination table is proposed, which provides the effective suggestions for the performance optimization of turboshaft aeroengine.

Calculation and Optimization of Volumetric Efficiency of Aviation External Gear Pump

The power consumption of aviation gear pump has a direct impact on the performance of aero-engine. To improve the efficiency of aviation external gear pump, this paper analyses the leakage of gear pump, and calculates the leakage of axial, radial clearance, gear face meshing clearance, and the elastic loss of liquid compression. Mathematical models of volumetric efficiency are established including the effect of temperature and pressure. Comparing the theoretical value with experimental results, the effectiveness of the models is verified with the error less than 5%. On this basis, the design variables of gear pump are optimized with the maximum theoretical displacement as the optimization objective function. The simulation results show significant volumetric efficiency improvement of the external gear pump. And some suggestions on actual products design and analysis in the aviation fuel device are proposed accordingly.

Inspection of blade profile and machining deviation analysis based on sample points optimization and NURBS knot insertion

As the core component of aviation industry, the machining accuracy of blade has great impact on the performance of aeroengine. Blade inspection can get knowledge of machining accuracy and can be used to compensate the machining error. In consideration of measuring time and efficiency, measuring trace planning based on sample points optimization (SPO) is introduced, and NURBS knot insertion (NURBS-KI) method is proposed to reconstruct the blade contour. Then, the designed model and the reconstructed model are compared to analyze the machining error. The reconstruction result shows that the presented method can better restore the blade contour, and NURBS-KI algorithm is proved in this paper to be an effective method to reconstruct blade curve and surface based on small number of measurement points. As illustrated in deviation analysis results, the machining error is within the design tolerance, and the finishing allowance can be removed afterwards.

Design of 1 + 1 / 2 counter rotating centrifugal turbine and performance comparison with two-stage centrifugal turbine

The counter-rotating turbine technology is one of the potential technical measures to improve the performance of aero-engine. Inspired by axial-flow counter-rotating turbine, this paper applied the counter-rotating turbine technology to the centrifugal turbine and carried out the aerodynamic design of the 1 + 1/2 counter-rotating centrifugal turbine stage by theoretical analysis using the air ideal gas as the working fluid. Then the blade profile of 1 + 1/2 counter-rotating centrifugal turbine was designed based on the velocity triangle obtained from theoretical analysis. At last, 1 + 1/2 counter-rotating centrifugal turbine was numerically analyzed and compared with the two-stage co-rotating centrifugal turbine under the same thermal parameters. The results show that the 1 + 1/2 counter-rotating centrifugal turbine has 12.0% less maximum diameter and 1.57% higher efficiency than the two-stage co-rotating centrifugal turbine.

Measurement of fastening force using dry-coupled ultrasonic waves

The accurate measurement of assembly fastening force of the high-pressure compressor rotor is of great significance to improve the structural connection quality and comprehensive performance of aero-engine. To solve the problem that liquid couplant reduces the measurement accuracy and causes the surface of the bolt to rust and corrode, a method of measuring the fastening force with dry-coupled ultrasonic wave was proposed in this paper. The measurement model of the fastening force including the thickness of the protective film of the ultrasonic transducer and the couplant was established, and the influence of the thickness variation in the couplant on the measurement accuracy of the fastening force was analyzed. Based on the propagation model of the ultrasonic wave on the heterogeneous interface and the principle of ultrasonic dry coupling, a coupling device was designed. At last, the experiment of fastening force measurement based on dry coupling and liquid coupling ultrasonic wave was carried out and compared. The experimental results show that the average relative errors of the fastening force measurement based on dry coupling and liquid coupling ultrasonic wave are 2.13% ± 0.42% and 3.15% ± 0.80%, respectively. Therefore, the dry coupling method can be as good or better in measuring the accuracy of the fastening force. Furthermore, it also overcomes the limitations of the liquid coupling method, which should make it more suitable to the measurement of fastening force in the aerospace field.

Effects research on theoretical-modelling based suppression of the contact flutter in blisk belt grinding

Blisk is one of the critical parts of aero-engine whose surface processing quality directly affects the performance of aero-engine. The vibration phenomenon usually happened in the novel open belt grinding, and seriously affects the dimension precision as well as the surface quality of the whole blade profile. In order to figure out that, this paper established a vibration model for the blisk belt grinding. The weak rigidity characteristics of the system were analyzed initially, and the vibratory mechanism was revealed from the view of dynamic analysis. Based on the theoretical model, the stability conditions were proposed by analyzing the influencing of vital factors on processing stability. The experimental validation indicated that the vibration signal waveforms during the process had been successfully reduced by introducing adjustment of grinding parameters. The profile accuracy of the blade contour edge was improved by 9.53 % from the range of −0.0376–0.1145 mm to that of −0.0359–0.1017 mm. After parameter adjustment, the smoothness of the micro-morphology of the blade surface was improved, and the roughness of the blade surface decreased from Ra 0.379–0.573 μm to 0.291–0.368 μm, which fully met the processing requirement of Ra <0.4 μm.

A repair strategy based on tool path modification for damaged turbine blade

Turbine blade plays an extremely important role in the aerodynamic performance of aero-engine. And the repair of damaged turbine blades is of great interest for aerospace industries due to continual increase in raw material and manufacturing costs. This manuscript presents a new repair strategy for damaged turbine blades based on tool path modification. The strategy basically involves three crucial procedures: rigid registration of nominal curve and measured points adjacent to damaged region, B-spline approximation of residual errors based on feasible region, and modification of the tool paths used for repairing machining. Rigid registration of nominal curve to measured points is accomplished using improved ICP algorithm adjacent to damaged region. B-spline approximation of residual errors is used to calculate smooth modification amount corresponding to cutter location points. And finally, modified tool paths are used for repair machining, including grinding and polishing. Tip repairing of a rotor turbine blade has been successfully performed to demonstrate the effectiveness of the proposed methodology. The error of repair machined trace between the repaired area and undamaged area is within 0.01 mm which commendably meets the repair machined requirement. And the repaired results have shown that the repairing strategy proposed in this paper is a reliable solution for repairing tip of turbine blades and can guarantee a surface smooth restoration with higher accuracy.

Effects of discharge status in AE-EDM of 8YSZ ceramic

Thermal-barrier-coated superalloys (TBCs) is generally used to make hot-end components such as aero-engine blade, because of its excellent thermal insulation and thermal shock resistance. The film cooling hole technology is applied on blade made of TBCs, which can further improve the service life and performance of aero-engine. However, it is difficult to realise one-step machining with traditional cutting techniques due to the high brittleness of TBCs. Electrical discharge machining (EDM) can not only machine any conductive materials, but also realise the machining of insulating materials. However, the properties of insulating ceramic materials are different with that of conductive materials. Existing discharge status detection mechanisms cannot effectively identify the EDM discharge status of insulating ceramic coating. Hence, in this study, discharge status of 8 mol.% Y2O3-stabilized zirconium (8YSZ) ceramic coating is investigated via assisting electrode method. Experiments with single-factor are carried out to investigate the effects of discharge status on gap erosion characteristics of 8YSZ ceramic with different peak current and pulse duration.The experiments result showed that discharge statuses of 8YSZ ceramic coating were dominated by low resistance discharge rate and high resistance discharge rate, the total discharge rate varied with low resistance discharge rate. Adjusting discharge gap with servo reference voltage, the total discharge rate increased with increasing low resistance discharge rate.

Online detection method for holes co-axiality of aero-engine

In recent years, the requirement for the assembly performance of aero-engine is getting higher in the aviation field. As the key indicator which can affect engine performance, the demand of detection accuracy of rotor bearing holes’ coaxial error is increasing. In the engine’s assembly process, the traditional manual mechanical detection cannot measure the assembled holes’ co-axiality directly, and must be carried out by the fixed tools after the trial assembly. This results in the long assembly time, low productivity, and low detection accuracy. An online detection method which can better ensure the products’ assembly quality must be proposed. Based on the analysis of the related research status of co-axiality detection at home and abroad, combined with the laser alignment technology and the axle hole centering measurement technology, an online measurement method based on the laser alignment is proposed, and a co-axiality detection system of the turbofan engine for specific models is introduced, whose centering error is less than 4μm. Besides, a universal co-axiality detection method of the engine rotor shaft hole is obtained, which could optimize the assembly process and improve the assembly efficiency.

LPV/PI Control for Nonlinear Aeroengine System Based on Guardian Maps Theory

The requirement of fighter’s maneuverability puts forward higher indexes for the control performance of aeroengine. It is generally recognized that the proportion integration (PI) control is the most commonly used control method of aeroengine. However, due to the high nonlinearity and performance requirements of aeroengine, the selection of PI parameters needs more accurate methods to satisfy higher performance requirements. In this paper, the linear parameter varying (LPV) model is established according to a nonlinear mathematical model of a turbofan engine. Then, the LPV/PI control based on guardian maps theory is proposed to solve the highly nonlinear aeroengine control problem which improves the response characteristics of aeroengine without changing the control method in the range of the scheduling parameters. In the process of design, a set of controller parameters satisfying the performance requirements is automatically generated by a given initial controller parameter, so designing the controllers at multiple equilibrium points is avoided. Finally, the simulations are performed by the integral separation of PI control at different points in the flight envelope for the nonlinear model. The results illustrate that the control method based on guardian maps theory can contribute significantly to solving the nonlinear problems of aeroengine control system.

Tool wear investigation in high-pressure jet coolant assisted machining Ti2AlNb intermetallic alloys based on FEM

The excellent mechanical properties of Ti2AlNb intermetallic compounds are beneficial to improve the performance of aero-engine. However, because of their high strength ratio especially at high temperature along with the low thermal conductivity of Ti2AlNb, the machinability of this material is poor. In this paper, high-pressure jet cooling technology is applied for the machining of Ti2AlNb intermetallic alloys to investigate the effects of high pressure jet cooling on the machinability of Ti2AlNb. The performance associated with the cutting force, the cutting temperature, the chip morphology and the tool wear have been discussed. The results showed that the high pressure jet cooling can enhance the heat dissipation by weakening the phenomenon of bubble adsorption in the cutting area based on the FEM simulations. The high pressure jet cooling can break the chip into C-type chip and improve the chip breakage capability. It also demonstrates that the crater wear and adhesive wear near the cutting edge can be significantly reduced with the high pressure jet cooling technology. When the jet pressure reaches 10 MPa, the cutting temperature reduced 22% and the tool life improved by 89%.

The Sliding Wear and Frictional Behavior of M50-10 wt.%(Sn-Ag-Cu) Self-Lubricating Materials at Elevated Temperatures

As the main steel used in the aero-engine main shaft bearings, the tribological properties of M50 can directly affect the performance of aero-engine. The purpose of this study is to design the reasonable composition of Sn-Ag-Cu alloy and investigate the wear mechanisms of M50-10 wt.%(Sn-Ag-Cu) composites (MSACC) prepared by SPS sliding against Si3N4 ball from 25 to 550 °C at 12 N-0.25 m/s. XRD, EPMA, FESEM and EDS mappings are conducted to understand the major mechanisms leading to the improvement in the sliding behavior of MSACC. The results indicate that MSACC with different specifications of Sn-Ag-Cu alloy shows excellent friction and wear properties from 25 to 550 °C compared to M50. M50-10 wt.%(50Sn40Ag10Cu) (MSACC-2) shows the distinguished tribological performance for the lower friction coefficients of 0.22-0.61 and less wear rates of 1.7-4.1 × 10−6 mm3 N−1 m−1, which is attributed to the formed excellent lubricating structure consisting of the lubricating film with massive Sn-Ag-Cu alloy and intermetallic compounds formed during the friction process, as well as the underneath mixed layer who can well support the lubricating film due to the good intersolubility between the designed Sn-Ag-Cu alloy and M50 (Fe).

Distributed collaborative probabilistic design of multi-failure structure with fluid-structure interaction using fuzzy neural network of regression

Abstract To improve the computing efficiency and precision of probabilistic design for multi-failure structure, a distributed collaborative probabilistic design method-based fuzzy neural network of regression (FR) (called as DCFRM) is proposed with the integration of distributed collaborative response surface method and fuzzy neural network regression model. The mathematical model of DCFRM is established and the probabilistic design idea with DCFRM is introduced. The probabilistic analysis of turbine blisk involving multi-failure modes (deformation failure, stress failure and strain failure) was investigated by considering fluid–structure interaction with the proposed method. The distribution characteristics, reliability degree, and sensitivity degree of each failure mode and overall failure mode on turbine blisk are obtained, which provides a useful reference for improving the performance and reliability of aeroengine. Through the comparison of methods shows that the DCFRM reshapes the probability of probabilistic analysis for multi-failure structure and improves the computing efficiency while keeping acceptable computational precision. Moreover, the proposed method offers a useful insight for reliability-based design optimization of multi-failure structure and thereby also enriches the theory and method of mechanical reliability design.