A multi-objective optimization study of the heat transfer and flow resistance characteristics of the miniature slit ribs in a rectangular channel was carried out. Four parameters were selected as the optimization variables: the slit width, the distance between adjacent slits, and the distance between the front and rear ends of the slit and the wall surface, and the Pareto optimal solution was obtained by using the non-dominated sorting genetic algorithm (NSGA-Ⅱ). The flow and heat transfer characteristics of the miniature slit ribs under the four optimization schemes on the Pareto optimal front surface were analyzed. The results showed that the optimized miniature slit ribs provided nearly the same heat transfer as the solid ribs, while the flow resistance was reduced, and the uniform heat transfer of the ribbed wall was significantly improved.

With an aim to develop a prediction model and obtain the key factors influencing the lean blowout limits in concentric staged combustors, experimental and theoretical investigations were conducted based on the flame blowout process inside a gas turbine combustor. The influences on the lean blowout limits of combustor geometry, atomization and conditions were investigated, and a method to optimize the flame stability performance was also proposed. An improved prediction model of the lean blowout limits was developed and validated. It was found that the co-swirl led to the larger recirculation zone, lower recirculated velocity and longer resistance time compared with counter-swirl, resulting in weak turbulent exchange between pilot and main flame. Consequently, the lean blowout performance of co-swirl flame was better than the counter-swirl flame. The maximum error of 20% was validated by comparing the annular and single dome combustor experimental data with the lean blowout model, which can be used in the stage of primary design of combustors.

A cooling structure for nozzle of a wind tunnel was proposed, that is: 24 channels were set on walls of anterior and posterior segments of the nozzle while staggered pin-fin structure was set on wall of nozzle throat area. The numerical simulation method of the conjugated heat transfer-structural thermal analysis was used to calculate and analyze the fluid flow, heat transfer, and stiffness performances of the overall nozzle structure. The calculation results showed that under the cooling water mass flow rate of 1 kg/s, the averaged cooling efficiency of the proposed cooling structure of the conceptual nozzle was 0.68% higher than that of the basic structure, and equivalent elastic strain of throat area of the nozzle was reduced by around 5%. The response surface model approximation method and multi island genetic algorithm were used to perform multi-objective optimization calculation of the conceptual nozzle. The results showed that the maximum wall temperature of the optimized structure was about 1.6 K lower than that of the conceptual one under the cooling water mass flow rate of 2.142 9 kg/s, and equivalent elastic strain of throat area of the nozzle was reduced by around 10%. The cooling structure design of the nozzle and its multi-objective optimization method may provide a reference for an effective thermal protection design of nozzle of wind tunnel.

In order to explore the effects of RP-5 and RP-3 fuels on the atomization performance of dual-orifice pressure-swirl atomizer, the research on the effects of properties such as flow rate characteristics, cone angle, Sauter mean diameter (SMD) and droplet velocity was carried out for the two kinds of fuels under different fuel supply pressures. The results showed that the flow rate of the RP-5 fuel nozzle was larger than that of the RP-3 fuel. The main fuel line flow differed by about 5%, and the primary fuel line flow differed by about 2%. The nozzle atomization cone angles of RP-5 and RP-3 fuels were basically the same. When the primary fuel supply flow rate was less than 8 kg/h, the SMD of RP-5 fuel was greater than that of RP-3 fuel. When the flow rate was greater than 8 kg/h, the SMD of RP-5 and RP-3 fuels were basically the same. With the continuous increase of the main and primary fuel flows, the SMD of RP-5 fuel was larger than that of RP-3 fuel and the difference continued to increase. With the increase of fuel supply pressure, the droplet velocity of RP-5 fuel was significantly higher than that of RP-3 fuel, all showing an “M”-shaped distribution.

In order to clarify the degradation index of the inerting of aircraft fuel tank, some literature of fuel tank ignition test were summarized and analyzed from three aspects: test facilities, test results and the reasons for the differences between different tests. According to the results of literature analysis, the inerting of fuel tank was divided into four grades. It was found that the differences of test facilities and ignition standards were the main reasons for the differences between different test results. The high-energy ignition source test had particularity in the aspects of explosion standard, test effect factors and test results, requiring for higher inerting ability of fuel tank. The inerting capacity of aircraft fuel tank could decrease with the increase of oxygen volume fraction in mixed gas, and the safety of fuel tank varied under different inerting conditions. The degradation of inerting capacity need to consider the effect of ignition source and mixed gas pressure at the same time.

In consideration of the intense aerodynamic heating during the flight of the high speed vehicles, the heat transfer process of a multi-layer thermal protection structure designed in the sequence of “high-temperature thermal protection layer + thermal insulation buffer layer + core thermal insulation layer” was investigated, and a one-dimensional unsteady thermal conductivity-radiation coupled heat transfer model was established inside the thermal protection structure at high temperature environment. The temperature profile of each layer of the thermal protection structure at high-temperature environment was obtained by numerical simulation. Based on the difference of thermal insulation performance of various thermal protection materials, the optimal design scheme with the total mass and thickness of the lightweight multi-layer thermal protection structure as the objective function under certain constraints was proposed, the optimal geometric parameters of the multi-layer structure were obtained, and the anti-insulation performance of the optimized thermal protection structure was verified experimentally. The experimental results showed that the optimized thermal protection structure can withstand 1 473 K for 1 800 s while the back temperature was kept below 370 K.

In the afterburner with high flow rate high, low pressure, oxygen poverty, the direct fuel injection is predominent, and the combustion model usually overestimates the reaction rate of the afterburner. Table-searching method is used in flamelet models with the advantage of fast calculation, but it is difficult to adjust the reaction rate. Based on the steady laminar flamelet model, unsteady chemical kinetic factors were added to adjust the reaction rate. Based on the experimental data, the key geometric parameters were established. The flamelet database was optimized, and the numerical simulation accuracy of this method was improved under high speed, low pressure, oxygen poverty and poor atomization effect. The results showed that the flamelet database formed by this optimization method can better simulate the complex chemical reaction process in afterburner. According to the calculation results, the simulation error of temperature distribution can be controlled within 15%, and the simulation error of average temperature can be controlled within 5%.

Rotating detonation experiments were conducted with various mass flow (i.e., 142.7−493.9 g/s) in a hollow combustor. The propagation velocity of the detonation wave was close to the Chapman-Jouguet (CJ) detonation speed when the mass flow reached 493.9 g/s. With the decrease of mass flow, the velocity and pressure of the detonation waves decreased. When it dropped to 142.7 g/s, the detonation waves evolved into a two-wave mode, accompanied by extinction and re-initiation phenomenon. Moreover, the pressure and velocity of the detonation waves fluctuated periodically, and the average propagation velocity was only 76.8% of CJ detonation velocity. Further, the nonlinear time-series analysis was adopted to reveal the stabilities of detonation waves. Results showed that when the mass flow was greater than 300 g/s, the attractor of the pressure time series in the phase space converged to the limit cycle mode. Decreasing the flow led to the disorder of the attractor. It indicated that the stability of the detonation wave decreased, and the system was prone to disorder. This study proved the effectiveness of nonlinear time-series analysis in studying the stabilities of rotating detonation, providing a methodological reference for the judgment of detonation wave stability under complex working conditions.

Based on model experiment verification, a numerical simulation method was used to study the effect of the structural parameters of an infrared suppressor’s two-dimensional mixing duct on the overall aerodynamic performance and temperature field of the infrared suppressor. Results showed that: within the scope of the parameters, with the increase of the outlet width of the two-dimensional mixing duct, the pumping coefficient of the two-dimensional ejector nozzle increased first and then decreased, and the average temperature of the bow-shaped baffle cold side increased by 24%. As the expansion angle of the two-dimensional mixing duct increased, the pumping coefficient decreased, and the average temperature of the bow-shaped baffle cold side increased by 3%. If properly extending the length of the straight section of the mixing duct, the pumping coefficient first slowly rose and then decreased, and the temperature change at the bow-shaped cold side was small. The key to improve the pumping coefficient is whether the main flow’s momentum can be effectively used and the flow separation of the main flow can be suppressed. In general, the surface temperature of the bow-shaped baffle cold side is affected by the internal eject flow of the bow-shaped baffle, the stagnation vortex downstream the bow-shaped baffle cold side, and the cold backflow at the narrow edge outlet of the two-dimensional mixing duct.

A performance simulation model of dual-bypass combined exhaust VCE was established by means of aerothermodynamics, and the performance simulation program was compiled to simulate the optimal variable geometry scheme in throttling state and maximum state under two configuration modes. The results showed that the specific fuel consumption of dual-bypass mode was lower 0.7%−2.5% and the thrust was lower 3.1%−5.5% than that of single bypass mode when the configuration was only variable. Performance benefit of the combined variable geometry scheme (scheme 4) with main nozzle, mixer and high-pressure turbine guide was the highest when the components geometry was only variable. Compared with the variable geometry scheme (scheme 1) of only variable main nozzle geometry, the specific fuel consumption under throttling condition of scheme 4 was reduced by 2.7%−3.2%, and the maximum thrust at high altitude was increased by 4.2%−5.2%. Performance benefit of the variable cycle scheme with combination of dual-bypass variable configuration and variable geometry scheme 4 can be further improved. Based on the performance of single bypass engine with individually adjustable main nozzle, the specific fuel consumption under throttling condition of the variable cycle scheme was reduced by 4%, and the maximum thrust at high altitude was increased by 5.2%. Based on the performance of dual-bypass engine with individually adjustable main nozzle, the specific fuel consumption under throttling condition of the variable cycle scheme was reduced by 3.2%, and the maximum thrust at high altitude was increased by 13.7%.

Numerical simulation method was used to simulate the aerodynamic characteristics of the entire aircraft with propeller slip flow in the internally blown boundary layer control scheme (inflation flaps), and compare them with the wind tunnel test results. The four propeller regions were divided into meshes separately, and data were transferred between each domain through surface overlapping mesh. Using the quasi-steady method based on multiple reference coordinate systems and the unsteady method of real rotation of the propeller, the lift-drag characteristics were calculated and compared with the wind tunnel test results. The results showed that the quasi-steady method can roughly capture the development trend of the lift characteristic curve, but the calculated specific value of the lift coefficient at a fixed angle of attack was far from the wind tunnel test results, and the stall angle of attack captured by this method was generally smaller than the test results, showing a large gap in resistance characteristics; the unsteady method can more accurately capture the development trend of the lift characteristic curve, and the specific value of the lift coefficient under the stall angle of attack and the fixed angle of attack was also more accurate, and the average drag error was controlled within 15%.

In order to improve the laminar flow area of the nacelle surface to reduce the drag, the parametric method of the profile based on PARSEC (parametric section) curve and genetic algorithm were used to optimize the nacelle, with its goal to push back the transition position of the nacelle. At the same time, the optimization results of nacelle under different Mach numbers were studied; the aerodynamic performance and drag divergence characteristics of the nacelle before and after optimization were compared and analyzed. The results showed that: the drag at the design point of the optimized nacelle was 2.25×10⁻³ lower than original nacelle, but the drag deterioration was more serious at the off design points of high Mach number, which led to the optimized nacelle drag divergence at lower Mach number.

For serial hybrid-electric aircraft (HEA), the flight performance of the whole aircraft was analyzed in combination with the dynamic characteristics within the given mission profile, and the overall parameters were associated with power and energy demand in each flight stage, assisting in design and sizing of each system component. Then, the calculation logic and each work path for the serial hybrid electric propulsion (HEP) system were summarized to explore the potential impact of energy management strategy (EMS) on the sizing method. Based on the established design system, a Dornier Do 228NG aircraft was selected and applied to compare the proposed method with that developed by two European teams from three design aspects. The results showed that the relative error for design point was less than 1.5%, the errors for conventional powertrain design were under 6%, and the evaluation of maximum takeoff mass (MTOM) for serial HEP design was less than 4% error. And it can verify the feasibility and effectiveness of our method. The characteristics, advantages and disadvantages of four EMS were analyzed and discussed. And based on an existing serial HEA, the Panthera Hybrid, the differences of power system working situation and design parameters under distinct strategies were studied and summarized. The results indicated that the MTOM under Light strategy was the smallest, and the benefits lied in that the maximum power demand during the take-off was taken by the fuel and battery power system at the same time, which optimized the power system weight directly.

In order to further explore the drag reduction effect of the turbulent boundary layer by the dielectric barrier discharge （DBD） plasma actuation, an experimental study was performed to reduce the flat plate turbulent boundary layer drag in a low-speed wind tunnel with a freestream velocity of 10.7 m/s. This experiment focused on the drag reduction of different pulsing frequencies on the flat plate turbulent boundary layer. The hot wire anemometer system was used to collect the streamwise velocity signal, and acquire the mean velocity distribution and fluctuation velocity distribution within the turbulent boundary layer. A comparative analysis of the experimental results showed that the plasma significantly reduced the mean velocity in the logarithmic region of the boundary layer, and as the pulsing frequency increased, the local drag reduction showed a trend of first increased and then decreased. When the pulsing frequency of 200 Hz, the maximum local drag reduction rate was 7.4%.

The aerodynamic design and performance simulation of a serpentine inlet with bypass were studied. The influence of alternating the first S-bend length on the inlet was explored. Through the analysis of the flow field and sand particles trajectories, the protype was modified. Then, on the basis of the modified benchmark model, the influences of different scavenge flow ratios and transition section area ratios on flow characteristics and sand separation efficiency in the inlet duct were emphatically studied by means of numerical simulation. The results showed that if the length of the first S-bend was too small, the aerodynamic performance was better but not favorable for sand separation; if the length was too large, the aerodynamic performance was worse but the sand separation effect was better. In the process of decreasing transition area ratio, the aerodynamic performance of inlet decreased slightly. When separation vortices were formed, the total pressure loss increased rapidly, but the outlet total pressure distortion coefficient decreased. And too large or too small area ratio was not conducive to the sand separation of inlet. With the increase of scavenge flow ratio, the performance of sand separation efficiency was improved, the total pressure recovery at the outlet was basically stable and the distortion was increased.

The remaining useful life prediction method based on attention mechanism and residual nested long-short-term memory （NLSTM） neural network was employed to address the shortcomings of traditional long-short-term memory （LSTM） neural network in the recognition and extraction of multi-dimensional data features. Two NLSTM neural network layers were used to replace the main structure of the residual block, and the shortcut connection of the one-dimensional convolutional network in the residual block was retained, which can fully extract the temporal feature and use the jump layer to transfer useful data in the network layer. The method also added the attention mechanism to construct multilayer network, and the important information influencing the result of prediction can be chosen to improve the prediction accuracy by the attention mechanism. The proposed method was verified by experiments in the aero-engines degradation dataset. The results showed that the method can effectively establish the relationship between the monitoring data and the engines health. The prediction error was reduced by 10.8% compared with the method without residual structure and reduced 18.9% compared with the method without attention mechanism, which improved the prediction accuracy effectively.

For the problem that the vibration signal of rolling bearing faults is disturbed by background noise and the fault features are not easily extracted, a combination of non-local mean denoising (NLM) based on the optimization of the gray wolf algorithm (GWO) and fully adaptive noise-enabled ensemble empirical modal decomposition (CEEMDAN) was proposed for bearing fault diagnosis. First, CEEMDAN and the Correlation coefficient-energy ratio-kurtosis criterion were used as preprocessing way, and signal reconstruction was performed; then the grey wolf algorithm was used to optimize the parameters of NLM, and the optimal parameters were used to denoise the reconstructed signal, and secondary denoising of the denoised signal was achieved through SG (Savitzky-Golay) filtering to obtain the final denoised signal, and envelope analysis of the final signal was performed to obtain diagnostic results. For the hybrid feature extraction technique of GWO-NLM denoising, CEEMDAN and envelope analysis, the signal-to-noise ratio was improved by 9.31 dB after denoising as shown by the simulated signal, and the fault characteristic frequency and multiplication frequency of the bearing and the series modulation frequency of the fault characteristic frequency and rotation frequency can be clearly extracted by the experimental signal.

In view of the current situation of low geometric accuracy and unstable quality of film cooling holes at home, experiments with different process parameters of femtosecond laser were carried out. The film cooling holes were analyzed based on the feature segmenting and point cloud fitting from slice image through computed tomography technology. Diameter and geometric features were tested and evaluated. The results showed that the diameter of the inlet of the film holes was slightly larger than that of the outlet with the process parameters of ultrafast laser, where the taper was between 0.005° and 0.020° for the testing detected by cone beam CT (computed tomography). The maximum position error was 0.072 mm. The incident angle of the special-shaped hole was roughly between 60° and 70°. It is reliable to use cone beam CT measurement method to detect and evaluate the geometric features of film cooling holes.

In order to study the prediction method of notch fatigue life of GH4169 electron beam welded joints, the fatigue tests of notched specimens were designed and carried out. Based on the critical distance theory, the fatigue life prediction method for different notch shapes of electron beam welded joints was proposed. The nominal stress-life curves of three notched specimens of GH4169 electron beam welded joints (U type, V-1 type and V-2 type) were obtained through tests. Based on the test results of V-2 notched parts, an inverse method of critical distance was proposed to determine the characteristic dimensions of GH4169 electron beam welding notched joints. The fatigue life of notched joints was predicted by the critical distance point method and the line method, respectively. The results showed that the critical distance point method had better adaptability to the notched joints. Further analysis showed that for different notch shapes, when the theoretical stress concentration coefficients were similar, better life prediction results can be obtained by using the same characteristic size in the double dispersion zone.

Taking the transonic nozzle guide vane of a radial-inflow turbine with expansion ratio of 5.0 for an advanced auxiliary power unit as the research object, the vane profile was optimized and cascade tests were conducted by eliminating the local ultrasonic region in front of the throat and weakening the shock wave intensity at the trailing edge. The research showed that by adopting the design idea of large positive incidence angle and small installation angle, and reducing the curvature of suction side before the throat, reducing the flow area of inlet duct, the load in front of the blade profile was improved, the over expansion area before the throat was eliminated, and the airflow acceleration was more uniform. A local concave structure was constructed behind the throat of the suction surface, which can transform one strong shock wave at the trailing edge of the suction surface into two relatively weak shock waves. The peak Mach number decreased, and the adverse pressure gradient at the trailing edge decreased, weakening the strength of the trailing edge shock wave. The test results indicated that the energy loss coefficient of optimized profile dropped as the cascade exit Mach numbers varied from 0.9 to 1.1, and the energy loss coefficient dropped nearly 20% when the exit Mach number was 1.1.

To overcome three major problems of high-dimensional, time-consuming, and black box in the optimization design of aggressive geared turbofan (GTF) engine booster, a set of accurate, efficient and reliable optimization design methods were developed. Using multi-objective particle swarm optimization combined with descending simplex algorithm, it had the advantages of fewer optimization variables, fast solving speed, and strong optimization ability. After optimized design, the peak efficiency and stall margin of the GTF booster were increased by 0.27% and 1.31% at 100% design rotational speed, respectively. Compared with the prototype of the highly loaded stator using composite sweep and lean, the optimized configuration of the highly loaded stator further changed the blade profile characteristics and three-dimensional stacking rules of the entire span. The flow separation from 20% of the span to the tip of the blade moved downstream, reducing the radial migration from the tip to the hub. It reduced the range of the low-speed recirculation region near the trailing edge of the suction surface, delayed the stall of the GTF booster, and improved the efficiency of the GTF booster.

To investigate the correlation between the tonal noise generated by rotor/stator interaction and the incoming upwash velocity of the stator, the tonal noise of a single-stage, low-speed axial compressor test rig (TA36) in a throttling process was studied by a well-developed inhouse hybrid noise prediction method. In order to accurately capture the source of the tonal noise, i.e., unsteady pressure fluctuation on the surface of the stator blade, the effects of the simulation grid and time-step size on the prediction of the unsteady pressure fluctuation were discussed firstly. Then, the variations of upwash velocity and tonal noise in the throttling process were compared. The result showed that at the third blade passing frequency (BPF) of the design speed, the amplitude variation of the incoming upwash velocity on the 70%, 80%, and 90% span of the stator was consistent with the sound pressure level predicted by the hybrid method, and kept good consistency with the experimental measurements. In addition, the sound radiation in the far field demonstrated significant directivity while the directivity did not change significantly with the mass flow rate.

As a traditional data classification algorithm, C4.5 Decision Tree has the advantages of simple calculation and high accuracy. Due to the fact that aircraft has many parameters and large amount of data, C4.5 Decision Tree requires multiple sequential scanning of continuous attribute values, but the classification time efficiency is low. To solve this problem, an approximate rough set resolution classification algorithm was proposed. Rough set approximation was used to determine the ability of attributes to divide sample data. According to the probability acquired, the attribute with the largest resolution was used as the split character to establish the classification decision tree. The algorithm improved the computational efficiency and reduced the generation of over-fitting problem while ensuring the accuracy of classification decision. Through comparative experimental analysis of multiple sets of data samples on UCI (University of California, Irvine) databases, it proved that the PSRP (rough set and resolving power) algorithm improved the average computational time efficiency by about 10% and reliability by 2% while ensuring the same accuracy.

In order to reduce the sudden change of speed caused by load disturbance arising from air flow and other factors on each propulsion motor in distributed electric propulsion aircraft, which results in sudden change of total thrust or inconsistent thrust on the left and right sides of the fuselage, it is necessary to ensure that each propulsion motor has good anti-interference ability and speed synchronization. To solve this problem, an improved cross coupling control strategy for dual permanent magnet motor system was proposed, and a sliding mode synchronous controller with improved reaching law was adopted. At the same time, a load observer was designed, which took the motor rotor position signal directly measured by the position sensor as the known quantity, and avoided the introduction of differential mutation. Finally, a series of simulations and experiments were carried out to verify the proposed control strategy of dual permanent magnet motor system. Simulation and experimental results showed that compared with traditional cross coupling control strategies, this control strategy reduced speed mutation by about 50% and synchronization error by about 18% in case of torque mutation, which proved that this control strategy had higher synchronization performance and stronger anti-interference ability compared with traditional cross coupling control strategies.

In view of the demand for the use of the motorized spindle of the precision grinder, the basic structure and operating conditions of hydrodynamic bearing were analyzed, and the calculation model of the static and dynamic characteristics of the hybrid bearing was established. The static characteristics included temperature rise, flow rate, load bearing force and power consumption, the dynamic characteristic parameter included a stiffness. The influences of structural parameters, radius clearance, throttle aperture, width-to-diameter ratio, working condition parameters oil supply pressure and rotate speed on the static and dynamic characteristics of hydrodynamic bearing were calculated and analyzed, then the calculated results were compared with the results of the laminar flow model and the test results. Research showed that: radius clearance was a more sensitive variable, which had a significant impact on temperature rise, reducing it by about 77.6%. Compared with throttle aperture and width-to-diameter ratio, radius clearance had the greatest impact on the performance of hydrodynamic bearing; rotating speed had a greater impact on the static and dynamic characteristics of hydrodynamic bearing. Obviously, the impact on temperature rise and power consumption was relatively large, increasing by 17.8 times and 18.1 times of the initial value respectively; the motorized spindle required for better cooling measures under high-speed working conditions.