In view of a shape memory alloy beam seal with elliptical arc groove in the female connector, the elastoplastic finite element thermodynamic coupling model considering the fluid pressure and temperature in the pipe was established by using ABAQUS software. The contact bandwidth and contact stress distribution between the female and male connectors were obtained by numerical simulation. Based on percolation theory and finite element contact analysis of micro rough sealing interface, the critical contact stress with zero leakage probability of shape memory alloy sealing interface was calculated. Combined with the contact stress distribution on the primary seal, S index was used as the evaluation criterion of the sealing performance of shape memory alloy beam seal. The effects of preload, fluid pressure and temperature on the sealing performance of shape memory alloy beam seal were numerically simulated. The results showed that within the range of assembly tightening torque, the sealing performance increased with the increase of preload; the sealing performance increased with the increase of fluid pressure in the pipe, indicating that it had good self-sealing feature; the sealing performance was basically stable within the fluid temperature range of −50— 200 ℃, which could meet the sealing requirements. Numerical analysis showed that shape memory alloy beam seal had better sealing performance than stainless steel and titanium alloy beam seal under the same working conditions.

In view of the lack of mathematical analysis means of dummy balance process for high pressure rotor of high bypass ratio aero-engine and the lack of basis for technical indexes of dummy rotor, a quantitative analysis method of dummy balance process was proposed. The rotor unbalance state was represented by the static and couple unbalance vector passing through the rotor center of gravity. The dummy rotor model including weight deviation, center of gravity position deviation, moment of inertia deviation and end runout deviation was defined. Combined with the dummy balance process of high pressure rotor and the principle of index balance, the mathematical model of rotor correction unbalance and index compensation was established. And, the initial unbalance of high pressure combined rotor was used to evaluate the dummy balance quality. Results showed that, the dummy balance can replace the combined balance, and the two balanced rotors had the characteristics of assembly interchangeability and unrestricted assembly docking angle; in this case, in order to control the dummy balance quality, the dummy rotor weight deviation should be within ±4%, the center of gravity position deviation should be within ±2 mm, the diameter and polar moment of inertia deviation should be within ±5%, and the end runout deviation should be less than 0.008 mm.

A thermal internal pressure test method based on gas-liquid loading was designed for the load-bearing test of aero-engine casing under temperature and internal pressure load. The gas-liquid loading device can decouple temperature and pressure loading. This device used high-temperature oil as the heating medium to heat up aero-engine casing through an electric heater with the same shape as the aero-engine casing. The pressure loading system used a high-pressure air source to pressurize the cavity of the device to achieve internal pressure loading on aero-engine casing. Quantitative control of pressure load was guided by theoretical analysis of pressure model. Tests showed that the method can effectively control the temperature and pressure loading accurately. While avoiding the difficulty of using hydraulic loading method to achieve high temperature loading, this method solved the problem of poor temperature uniformity in the test using air-pressure loading method. This method also effectively avoided the blasting phenomenon if the air-pressure loading method applied to the destruction test. Results showed that the test method based on the gas-liquid loading method can be effectively applied to the thermal internal pressure test of aero-engine casing. The control accuracy of temperature load was better than ±3 K. The pressure loading process can be quantitatively controlled.

In order to research the dynamic similarity problems of rotors with squeeze film damper (SFD), which are common in aero-engines, a similar modeling method was established. Starting from the vibration differential equation of the rotor with damping, the similar relationship between the unbalanced force and the damping force in the rotor vibration process was derived by equation analysis method. Based on the oil film force and oil film equation of the squeeze film damper, the mathematical relationship between the parameters of the squeeze film damper and the similar parameters of the rotor was established, and the corresponding engineering design method was given. Taking a single-rotor system of the rotor as an example, a similar rotor system with a squeeze film damper was established. The dynamic characteristics of the rotor system and its similar systems were analyzed using the finite element method. The analysis results showed that the unbalance response error between the similar system and the original rotor system was lower than 1% when only considering the damping of squeeze film damper in the rotor system.

To address the shortcomings of the current calibration method for fluorescent oil film grey scale and thickness (tiny height device method) with complex acquisition conditions and a long calibration period, an approximate measurement method was proposed, by which only a very small amount of calibration data were required to achieve similar results to the current calibration method. The Elman dynamic neural network was used to extend the range of the small sample data and a one-dimensional interpolation algorithm was introduced to smooth the extended data items. The solved 3D fluorescent oil film thickness data were smoothed twice using a two-dimensional interpolation algorithm to obtain a complete thickness distribution. The simulation results showed that the thickness measurement by this near-efficient method can finally display the fluorescent oil film thickness distribution clearly, accurately and quantitatively, and the effect was similar to that of the currently widely used tiny height device method, with the maximum error not exceeding ±2.5 μm at the pool of fluorescent oil film (thicker area), and not exceeding ±2 μm in the smooth and moderate and thinner area; hence the engineering measurement standard of fluorescent oil film thickness could be met. It provides a calibration idea for the global friction measurement of aircraft, and has certain practical engineering application significance.

The application of composite materials is the main way to reduce aero-engine mass. Adhesive bonded repair was used to repair the damage of composite bypass casing of aero-engine, which was caused by different load cases and environmental conditions. A finite element model based on three-dimensional progressive damage method was constructed by Abaqus for the composite bypass casing of aero-engine of adhesive bonded repair, which simulated the propagation and evolution of composite material damage near holes and flanges, and predicted the static tensile and compression strength of resin-injection repair and scarf repair. Results showed that resin-injection was applied to repair the aerodynamic shape when the damage did not exceed 10% of the thickness while scarf repair was used to regain the static strength when the damage exceeded 10% of the thickness to penetration.

Targeting the phenomenon of non-reacting flow self-excited oscillation in a traditional cavity with a length-to-depth of 10.0 under the isolator entrance condition of Mach number 3.0, a scheme to suppress the oscillation by adding a rib in the cavity was proposed. Through experiments and numerical calculations, the effect of this scheme on suppressing oscillation was verified, and the differences in the flow field structure and combustion performance of the combustor with/without the rib were analyzed. It was found that adding a rib in the cavity can effectively eliminate the self-excited oscillation of 175.8 Hz under the non-reacting flow condition, and the reacting flow field was more stable. The flame stabilization ability of the cavity was reduced after the rib was added, and some kerosene not completely burned in the cavity continued to react after entering the divergent section, so as to extend and enlarge the combustion zone downstream. The combustion efficiency and net thrust of the engine were reduced by 5.4% and 8.9%, respectively, but the thrust was more stable. The peak value of one-dimensional averaged heat flux was also reduced from 2.9 MW/m² to 1.8 MW/m², which optimized the thermal environment of the combustor.

The effects of anti-carbon deposition structure on fuel distribution of aero-engine combustor double-way nozzle were investigated numerically and experimentally. Firstly, optical distributed spray detection system was applied to measure the fuel distribution, and the spray cone angel, circumferential and radial distribution of the section 20 mm downstream the nozzle outlet were obtained; the numerical simulation of the nozzle with different anti-carbon deposition structure was carried out by using VOF simulation method. The results showed that, under the same fuel pressure, the spray cone angel and peak radius of radial distribution decreased, while the proportion of fuel in the small radius increased, considering the effect of anti-carbon deposition structure of nozzle. The numerical calculation results were in good agreement with the experimental results, which can effectively explain the effect of anti-carbon flow on fuel distribution. Under the same fuel pressure and air pressure, when the nozzle was matched with different anti-carbon deposition structures, the spray cone angel was related to the velocity of the center airflow at the nozzle, and the circumferential distribution was mainly related to the gas-liquid ratio.

The frosting and defrosting performance of the microtubule compact precooler was studied under the experimental conditions of the flow velocity, the humidity value and the temperature of the main flow of 10 m/s, 6.4 g/kg and 50 ℃, respectively. Under the defrosting experimental conditions, anhydrous methanol was utilized as the solvent for defrosting, and anhydrous methanol with three different mass ratios (0.75, 1.0 and 1.25) was sprayed into the main flow for defrost the precooler during the defrosting experiments. The frosting and defrosting performance, the pressure loss coefficient, the wall surface temperature of the precooler tube bundles, and the heat transfer rate of the precooler were analyzed in detail. The experimental results revealed that when the cryogenic coolant flowed through the inside of the microtubule bundles of the precooler, the frost later quickly condensed on the outside of the precooler, and the frost layer gradually accumulated with the experimental time. However, once anhydrous methanol of three different mass ratios was sprayed into the main flow, the defrosting effect was obviously improved, the pressure loss coefficient of the main flow was significantly decreased and the heat transfer rate of the precooler was evidently increased. In addition, in the defrosting experiments, the wall surface temperatures of the precooler tube bundles were also significantly increased higher than the freezing point of water, making the spraying anhydrous methanol produce defrosting effect. Among three different mass ratios of the sprayed anhydrous methanol, the best defrosting performance was obtained when the mass ratio of the sprayed anhydrous methanol was 1.0. Moreover, based on analysis of the defrosting experimental results, it can be further inferred that the optimal mass ratio to achieve the best defrosting performance may be between 1.0 and 1.25.

The liquid spray distribution characteristics of a kind of integrated strut flameholder (ISF) with cross injection were studied with water, under the conditions of ambient temperature and pressure, incoming flow Mach number 0.182 and liquid-air momentum ratio range from 10 to 70, using laser sheet/photography. The effect of liquid-air momentum ratio and injection position on the distribution trajectory of liquid spray was discussed. The results showed that the outer trajectory of the liquid spray of ISF was similar to that of the crossflow, and the inner trajectory was bent back to the recirculation zone owing to the entrainments of the recirculation zone, which was more significant for low liquid-air momentum ratio condition. The liquid-air momentum ratio served as an important factor for inner and outer trajectory of the spray; the penetration depth of the liquid spray of ISF increased with the increase of liquid-air momentum ratio. The injection position of ISF had little influence on the outer trajectory of the liquid spray, but had a significant influence on the inner trajectory. It was not good for the entrainments of spray into recirculation zone when the injection distance was too far or too close, which was related to the closely coupling of the liquid injection and the flameholder.

Numerical simulations of the primary atomization in the gas-liquid pintle injector were conducted, using the VOF (volume of fraction) method with the adaptive mesh refinement to capture the gas-liquid interface. The realizable k-ε turbulence model was adopted for the turbulence modelling. The entire breakup process and the gas-liquid interaction at different instants were captured. The numerical results were qualitatively and quantitatively in good agreement with the high-speed photograph measurement results, which verified the accuracy of the numerical method. The breakup process and mechanism of the primary breakup and atomization were studied by analyzing the evolution of the gas-liquid interface, the vortex structure of the flow field and the velocity field in the pintle injector. The results showed that the formation of the liquid bridge was mainly caused by the expansion, stretching and coalescence of the liquid hole, while the droplet was mainly caused by the stretching of the central liquid sheet, the fractures of the liquid ligament and liquid bridge. The fracture and displacement of liquid sheet was mainly attributed to the vortex structure formed in the liquid sheet breaking stage.

Based on a flow-ignition platform, laser ignition experiments were carried out on the propane/air lean premixed gas for different equivalence ratios and velocities of flow. The study found that with the increase of the equivalence ratio and velocity of flow, the flame development speed increased and the flame area increased; the CH* luminous intensity in the flame increased significantly with the increase of the equivalence ratio, and the stage of flame development could be judged by the CH* distribution and luminous intensity changes. The probability of successful breakdown and ignition of the mixed-gas increased with the increase of the equivalence ratio and the velocity of flow, but the change of the equivalence ratio had a greater impact on the probability than the velocity of flow; the changes of the content of each component in the mixed gas could be judged by the H/N peak intensity ratio in the breakdown emission spectrum, and the calibration line could determine the equivalence ratio of the unknown premixed gas.

In order to explore the applicability of slot casing treatment in counter-rotating compressors, the effects of slot casing treatment on the aerodynamic performance and stability margin of a counter-rotating compressor were investigated by numerical simulation. The effect of the slot casing treatment on overall performance of the compressor and tip flow field was analyzed to reveal the stall margin improvement mechanism of the slot casing treatment in the counter-rotating compressor. The study showed that the slot casing treatment can improve the stability margin of the counter-rotating compressor, and the axial position of the casing treatment had a significant impact on the aerodynamic performance and stability margin of the counter-rotating compressor. With the forward movement of the casing treatment, the peak efficiency loss of the counter-rotating compressor gradually decreased, while the stall margin improvement was not much different. The combined effect of bleed and injection of the slots slowed down the degree of blockage in the rotor R2 blade tip passage, and achieved stability improvement by suppressing the development of tip leakage flow and secondary leakage flow. In addition, the slot casing treatment may change the first stall stage of this counter-rotating compressor, demonstrating the effectiveness of slot casing treatment in the expansion of stability under variable operating conditions.

Taking the dynamic outlet pressure of the 800 kW centrifugal compressor during the period of transition from steady state to surge state as the research object, the empirical wavelet transform combined with sample entropy characteristics was used to analyze the complex characteristics of the system under different working conditions. First, on the basis of analyzing the characteristics of the dynamic pressure waveform of the system, the empirical wavelet transform combined with the Pearson correlation coefficient was used to extract the signal. Second, the relationship between the sample entropy of the extracted signal and the change of the system working state was analyzed to discuss the influence of the decomposition layer of the empirical wavelet and the dimension of the sample entropy on the analysis result. Finally, white noise was added to the original signal to verify the anti-interference performance of the method. The research results showed that when the system entered the surge state from the steady state, the sample entropy of the system outlet dynamic pressure showed an obviously sudden change characteristics, and its value changed from 0 to about 0.7. From the perspective of the selection of system parameters, the change of sample entropy dimension had little effect on the analysis of system characteristics. In addition, this method had better anti-interference performance.

A multi-stage axial flow compressor was studied by numerical simulation to determine the effect of tip clearance and damper table on its aerodynamic performance. The influence principle of tip clearance change on tip leakage flow was revealed, and the relative magnitude of the influence of rotor tip clearance change on the performance of multi-stage axial compressor was analyzed. It was found that for the studied multi-stage axial flow compressors, the change of the tip clearance of the fifth stage rotor had the largest impact on the compressor performance. Stage efficiency decreased by 1.72% when the tip clearance increased from 0.390 mm to 1.007 mm. There was a maximum reduction of 0.6% in other stages. Furthermore, the first-stage and fifth-stage rotor blade damper tables were investigated for their effects on compressor performance. The influence of the damper table on the flow field structure and flow capacity was analyzed, and the mechanism of the damper table affecting the performance was revealed. The results showed that when there was the damping table, the peak efficiency, peak pressure ratio and choke flow rate of multi-stage axial flow compressor decreased; as the peak efficiency decreased by 1.6%, the peak pressure ratio decreased by 1.2%, and the choke flow decreased by 1.2%. Especially, the efficiency of the first and fifth staged decreased obviously, the efficiency of the first stage decreased by about 5.2%, and that of the fifth stage decreased by about 1.6%. As a result of the damping table, the pressure loss was caused, the density flow and flow capacity decreased.

To study the tip clearance flow instability of evolution and the physical mechanism of the compressor, a single stage axial compressor experimental rig was taken as the research object. Using the dynamic pressure sensors in the casing wall, the oscillating characteristics of tip flow field were acquired. The unsteady development of flow details was obtained by full channel calculations. It was found that with the decrease of the flow rate, the internal flow of the compressor went through three phases: steady state, rotating instability and rotating stall. The two pivotal activities of the tip clearance vortex were related to the transformation of the instability mode. When the tip clearance vortices propagated to the trailing edge of the neighboring blade, it began to fluctuate under the interference with the neighboring blade, resulting in small scale disturbance propagating along the circumference, that was, rotational instability. In near-stall state, the interface between tip clearance vortices and incoming flow exceeded the inlet of the blade channel, leading to leading edge overflow, which was accompanied by periodic production, circumstantial migration and attenuation of leading edge radial vortices. At this time, the leading edge radial vortices were almost uniformly distributed along the circumferential direction, which constituted the organized propagating disturbance. However, as the flow rate further reduced, the organized propagation of the leading edge radial vortex was destroyed, forming the distribution feature of local aggregation, leading to the stall cells with stronger local blockage and higher entropy.

In order to reveal the difference between the stability enhancement mechanism and the loss of different forms of casing treatment, a two-stage counter-rotating axial flow compressor (CRAC) was taken as the research object, the stability enhancement mechanism of self-recirculating casing treatment (SRCT) and axial slot casing treatment (ASCT) was studied by unsteady numerical simulations. The results showed that both SRCT and ASCT significantly improved the stall margin and total pressure ratio at the near-stall point, and increased the efficiency loss at the peak efficiency point. The casing treatment reduced the dynamic-dynamic interference effect between the two rotors by acting on the tip leakage flow and suppressing the pressure potential flow. The flow in axial slots was related to the relative position of the rotor. The periodic sweeping of the rotor to the casing treatment slots increased the unsteadiness of flow in casing treatment slots, and the mixing of the flow in casing treatment slots was the main reason for the decrease of efficiency.

In order to study the difference and mechanism of the internal flow total pressure loss between the boundary layer ingestion (BLI) inlet and the conventional S-shaped inlet, numerical simulation method was applied and step-by-step comparative analysis of the total pressure loss was carried out. The results showed that, when fan-face Mach number was kept unchanged, the flow loss of BLI inlet was larger than that of the conventional S-shaped inlet under the working conditions of relatively lower and higher Mach number of free-stream (corresponding to below 0.3 or above 0.6), and the maximum difference was 2.4 percent. Under the working condition of medium Mach number of free-stream (corresponding to between 0.3 and 0.6), the flow loss generated by the BLI inlet was slightly smaller than that of the conventional S-shaped inlet, and the maximum difference was 0.3 percent. The combined effect of the fore-wall of the BLI inlet and the low-energy boundary flow changed the flow characteristics in the inlet and developed rapidly in the diffuser of the S-shaped pipeline, leading to the difference in flow loss characteristics.

In order to master the law of aerodynamic interaction between stages of coaxial contra rotating propeller, reduce the intensity of aerodynamic interference between propellers and improve the aerodynamic performance of coaxial contra rotating propeller, the effects of 4 stage spaces between front and rear rows of 6×6 contra rotating propeller on aerodynamic interference were studied based on Reynolds averaged unsteady Navier-Stocks equation method and sliding mesh technique. The results showed that: the average propulsion efficiency of the coaxial contra rotating propeller was the highest when the stage spacing was 0.25 times of the propeller diameter. In addition, the efficiency fluctuation caused by aerodynamic interference was smaller. With the increase of stage spacing, the intensity of aerodynamic interference of front and rear propellers decreased. Compared with the rear propeller, the thrust pulsation of front propeller caused by aerodynamic interference was more sensitive to stage spacing. It can be seen that the stage spacing of coaxial contra rotating propeller had an obvious impact on the aerodynamic interference of propellers. Appropriate stage spacing in the design of coaxial contra rotating propeller is important to improve the aerodynamic performance of contra rotating propeller.

To improve the overall efficiency of automatic variable pitch propeller electric propulsion system, the optimal power control law was introduced: automatic variable pitch propeller electric propulsion system can adjust both the pitch angle and rotation speed simultaneously according to the flight conditions and thrust demand, and finally obtain a pitch angle/rotation speed combination, so that the propulsion system can meet the thrust demand and achieve the minimum power consumption, ultimately achieving the goal of minimum energy consumption control in the whole flight profile. To verify the effectiveness of the method, the same electric propulsion system was used to complete the same mission profile with the optimal power control law and the constant speed control law, then the propeller propulsion efficiency, motor efficiency, total electric propulsion system efficiency and electric propulsion system energy consumption data under the two control laws were obtained. The results proved that the optimal power control law can effectively improve the electric propulsion system efficiency and reduce the energy consumption compared with the constant speed control law, and the energy consumption of the same mission profile was reduced by about 6.3%.

The combined effect of the reverse thrust and weight increase of the thrust reverser on the deceleration performance of a civil aircraft was analyzed. A hypothetical turbofan model based on the CFM56 engine was established by Turbomatch software from Cranfield University, with A320 aircraft taken as the model. The propulsion system weight was estimated using the fan and turbine diameter. After discussion of aircraft deceleration benefit on the dry runway or icy runway, effects of the deflection angle and runway condition on the deceleration distance during conventional landing phase were analyzed. It showed that the thrust reversers were more efficient with small deflection angel. Based on a deflection angle of 55°, 10° reduction resulted in a deceleration benefit of approximately 7%. And the thrust reversers were more beneficial on the wet/icy runway, with the distance and time down by about 41% and 32% compared with the dry runway.

Scramjet free-jet tests were conducted in milliseconds in the high-enthalpy shock wave wind tunnel (FD-14A) of China Aerodynamics Research and Development Center at the conditions of replicating flight Mach number 10 and dynamic pressure of 30 kPa. High-speed schlieren and high-speed photography were employed to record the shock waves at the inlet lip and flame spreading process in the combustor, respectively. The free jet test process was analyzed by the optical measurement, scramjet wall pressures and heat fluxes. The ignition and combustion tests were conducted with different equivalent ratios of hydrogen. Distributions of pressures and heat fluxes along the engine wall indicated that ignition and stable combustion were achieved within a wide range of fuel equivalent ratios from 0.50 to 1.37.

Based on the data of China Airworthiness Directive (CAD) in 1996−2019, the evaluation indexes were constructed with the typical failures obtained by correlation analysis. The boundary conditions of whitening weight function were determined by risk coefficient, and the weight of each index was determined according to the principle of maximization of deviation. A safety risk assessment model based on grey whitening weight clustering was proposed. The grey prediction model was constructed by using the index data of equal time interval, and the prediction accuracy was improved by 2.88% by optimizing the weight value. The predicted number of failures was consistent with the actual occurrence, which proved the accuracy of the prediction model. Accordingly, improvement and prevention measures can be put forward to reduce the occurrence of faults.

Based on dynamics analysis of angular contact ball bearing, the nonlinear differential dynamic equations and the theoretical formula of friction torque for the bearing assembly of control moment gyro with revolution-rotation coupling were established. The influences of cage structure, raceway processing accuracy and preload on friction torque characteristics of the bearing assembly of control moment gyro were studied. The mechanism of abnormal fluctuation in friction torque of a certain bearing assembly of control moment gyro was also analyzed. The analysis results showed that the rub-impact between the outer diameter surface of cage and the guide rib of ring, and that between ball and cage pocket were main factors that triggered the abnormal fluctuation in friction torque of the bearing assembly of control moment gyro. A reasonable original radial clearance of bearing can effectively eliminate the rubbing phenomenon between the outer diameter surface of bearing cage and the guide edge of the ring, and avoid obvious abnormal fluctuation in friction torque of the bearing assembly of control moment gyro.