Based on a turbulence model experimental validation, some numerical simulations were conducted to investigate the effect of plug film cooling on cooling and aerodynamic characteristics for a 2-D plug nozzle. In this study, two cooling schemes namely the half-covering and full-covering film cooling were designed and involved. For each cooling configuration, the effects of perforated percentage (ranged from 0.5% to 2.0%) and non-dimensional inlet total pressure (ranged from 1.02 to 1.20) of coolant on the cooling and aerodynamic performances are discussed separately. The results confirm that an obvious reduction of plug temperature is achieved under both cooling schemes. While the full-covering film cooling configuration performs better, especially at the plug trailing edge where shock waves occurred. Within the scope of the investigation, a small perforated percentage of 0.5% is favorable due to its superior ability to improve the pressure difference between mainstream and coolant; inversely, a big perforated percentage leads to the coolant flow resistance increasing, which may cause the mainstream to flow back at the plug trailing edge. Rising the inlet total pressure of coolant could enhance the cooling performance but also deteriorate the aerodynamic performance of nozzle. Specifically, compared with the case without cooling configuration, the non-dimensional inlet total pressure of coolant ranged from 1.02 to 1.20, the surface temperature of plug decreased by 20% - 45%; the total pressure recovery coefficient decreased by 0.22% - 1.26%.
Aiming at the difficulty of extracting fault features on the aircraft landing gear hydraulic system, traditional feature extraction methods rely heavily on expert knowledge, and the accuracy of fault diagnosis is difficult to guarantee. This paper combined convolutional neural network (CNN) and support vector machine classification algorithm (SVM) to propose a fault diagnosis model suitable for aircraft landing gear hydraulic system. The diagnosis model adopted the one-dimensional multi-channel CNN network structure, took the original pressure signal of multiple nodes as input, adaptively extracts the feature value of the pressure signal through CNN, and built a multi-feature fusion layer to realize the feature fusion of the pressure signal of each node. Finally, input the fused features into the SVM classifier to complete the fault classification. In order to verify the proposed fault diagnosis model, a typical aircraft landing gear hydraulic system simulation model was built based on AMESim, and several typical fault types such as hydraulic pump leakage, actuator leakage, selector valve clogging and accumulator failure were simulated, and corresponding Fault type data set, and use overlapping sample segmentation for data enhancement. Experiments show that the diagnosis accuracy of the proposed fault diagnosis algorithm can reach 99.25%, which can realize the adaptive extraction of the fault features of the aircraft landing gear hydraulic system, and the features after multi-dimensional fusion have better discrimination, compared with traditional feature extraction methods more effective and more accurate.
The inverse method of characteristics (iMoC) is often employed to simulate the axisymmetric flow behind a predefined shock wave shape. Firstly, two marching schemes of iMoC were compared in this work: the intersection of the left- and right-running Mach lines and the intersection of the left-running Mach line and streamline. The intersection of the left-running Mach line and streamline is discovered to be simpler and more stable. Following that, the applicability of iMoC was analyzed by dividing the shock wave shapes into concave and convex curves, respectively. Based on the oblique shock relations, it is proved mathematically that iMoC is capable of computing the flow behind a concave shock wave. However, for the convex shock wave, if the shock wave angle declines too much along the axial coordinate, the clusters of left-running Mach lines may intersect, leading to iMoC failure. Furthermore, a method for enabling the implementation of iMoC is proposed by generating an expansion fan to replace the infeasible segment of the convex shock wave. Finally, computational fluid dynamics techniques were applied to validate the proposed methods and analysis. This study provides theoretical support to promote the application of iMoC in waverider and inward inlet design.
Aiming at the key scientific problems of strengthening cooling and heat dissipation of turbine blades, a new type of corrugated channel cooling structure was proposed in this work. Refined numerical simulation was carried out in six different corrugated channels, and the physical mechanism of flow and heat transfer was analyzed in detail. The results show that the corrugated channel has smaller flow resistance than the ribbed channel. Among the corrugated channels, the heat transfer effects of sinusoidal, triangular, and sawtooth2 corrugated channels are stronger than rib corrugated channel at the high Reynolds number, and these effects are distributed evenly. Within the six kinds of corrugated channels, the sinusoidal corrugated channel has the best comprehensive heat transfer effect. The blades with sinusoidal corrugated channels have better cooling effect due to the significant increase in heat transfer coefficient on the inner channel surface, and the channel contraction area plays a decisive role in the enhancement of the cooling effect. The heat transfer capacity of the sinusoidal corrugated channel is closely related to the shape of the corrugation, and the heat transfer effect reaches for the best near the waveform H/L = 0.115. The physical mechanism of heat transfer enhancement of the corrugated channel is revealed in this paper, which can provide a reference for the design of the cooling structure of aeroengine blades in the future.
The double-wall cooling as one of the most important cooling techniques of the hot-end components of aeroengine, the heat transfer performance of double-wall cooling structure can be significantly enhanced by the combination of jet impingement cooling and pin fins. Therefore, the double-wall cooling structure with jet impingement holes and pin fins has very important engineering application value. For the double-wall cooling structures with jet impingement holes and pin fins, the experimental studies have been carried out based on various of geometrical and flow parameters. Furthermore, the corresponding numerical simulations have also been carried out according to the corresponding experimental study conditions. In order to approximate to the real double-wall enhanced heat transfer structure of the hot-end components of the aero-engine, in present experimental and numerical studies, the double-wall enhanced heat transfer structure with the double-side outflow channel and the advantage of structural symmetry is adopted. Based on the numerical simulation results, the internal flow field structure, the flow resistance characteristics and the interior enhanced heat transfer performance of the double-wall cooling structure with jet impingement holes and pin fins are analyzed in detail. In addition, the main reasons why the pin fins can enhance the heat transfer performance of the double-wall cooling structure that with jet impingement holes and pin fins are further revealed. Actually, the enhanced heat transfer performance of the double-wall cooling structure is the results of the interactions between the internal jet impingement cooling, the internal crossflow and the turbulent flow of pin fins. Moreover, the influences of the jet impingement Reynolds number (Re), the non-dimensional row spacing (X/D) and the nondimensional hole pitch (Y/D) of jet impingement holes, and the dimensionless diameter (Dp/D) of the pin fins on the enhanced heat transfer performance, the internal flow characteristics, the distributions of local Nusselt number Nu and the flow resistance characteristics of the double-wall cooling structure with jet impingement holes and pin fins are further revealed. Importantly, for all numerical simulation conditions, the distribution differences of the enhanced heat transfer performances on the wall surface of the pin fins and on the wall surface of the jet impingement target plate with the variations of the geometrical parameters and the flow parameters are analyzed in detail. The numerical results indicate that the area-averaged Nusselt number N- u on the wall surface of the pin fins is higher than that on the internal wall surface of the jet impingement target plate. With the increase of the pin fins diameter Dp/D, the N- u on the whole internal wall surface of the double-wall cooling structure presents a tendency of firstly decrease and then gradually increase. In addition, the N- u on the entire interior wall surface of the double-wall cooling structure decreases with the increase of row spacing X/D, but it is not sensitive to the variation of hole pitch Y/D. Moreover, for the discharge coefficient of the double-wall cooling structure, it gradually increases with the increase of the jet impingement Reynolds number Re, the row spacing X/D and hole pitch Y/D of jet impingement holes, but it decreases with the increase of the diameter D-p/D of pin fins. Finally, for 3 <= X/D <= 5, 3 <= Y/D <= 5, 1 <= D-p/D <= 2, and 9000 <= Re <= 30,000, a correlation of the areaaveraged Nusselt number N- u is given, which is in good agreement with the experimental results.
