Liu Zhenxia

Pattern and phase selection of peritectic reaction during directional solidification

Based on the growth competition between different pattern and phases, the pattern and phase selection during peritectic solidification is analysed by applying the maximum interface temperature criterion to the interface response functions calculated from a numerical model for single phase solidification. The theoretical results agree very well with the experimental results published in literature.

The design and performance evaluation of axial ventilator with honeycomb in the turbofan engine lubrication system

Numerical simulations have been carried out to investigate the performance of the axial ventilator equipped with honeycomb structure. The oil /air two-way coupling model based on the Realizable k–ɛ turbulence model and the droplet impact model are proposed. Based on verifying the rationality of numerical model, characteristics of flow resistance and oil–gas separation efficiency are calculated and analyzed. The results show that the axial ventilator with honeycomb has favorable separation efficiency, which is estimated as 99.6% for the oil droplet diameter of 5 µm. The honeycomb structure has little effect on flow resistance, but plays a major role in the oil–gas separation of axial ventilator, where the contribution to the oil separation accounts for 80% at least. Besides, the increase of rotation Reynolds number enhances the centrifugal force, resulting in the increase of separation efficiency, while the increase of nondimensional mass flow rate and environmental temperature reduce the residence time of oil droplets in the axial ventilator mainly, resulting in the decreasing of separation efficiency.

Numerical and Experimental Study for Unsteady Oil Film Thickness of the Rotating Cylinder Chamber Wall

The oil film thickness on the bearing chamber wall directly affects the wall heat transfer efficiency, so a fundamental study on the motion of oil film on the rotating cylinder has been conducted to this end. On the one hand, the rotating cylinder test rig was designed, and an ultrasonic measurement system was established to measure the dynamic oil film thickness. On the other hand, the unsteady oil film heat and mass transfer movement model was also established, and the numerical simulation to solve oil film motion by using computational fluid dynamic (CFD) commercial software was carried out. Meanwhile, on the basis of study on the oil film formation process and film thickness verification, the oil film distributions on the chamber wall with rotation speed and oil flow rate were analyzed and studied. Results show that the oil film on the rotating chamber wall experiences a development process from the oil film formation to basic stability, about 1.0 s in this paper. And comparison between the numerical and experimental data shows that the maximum error between experimental data and numerical simulation is 7.76%. Moreover, for the oil film distributions in the stable state, oil film thickness shows a trend of decreasing with the increasing of rotation speed, but increasing with the increasing of oil flow rate. The research here will provide the basis for subsequent study of the interaction between oil film motion and the wall heat transfer.

Numerical Study on the Improvement of Oil Return Structure in Aero-Engine Bearing Chambers

Abstract Numerical study has been carried out to improve the unreasonable oil film accumulation and oil return effect of the bearing chamber. Ramp sump and eccentricity sump offtake structures are designed and improved, and oil-gas two-phase flow calculation model based on CLSVOF (coupled level set and volume of fluid) method is proposed. Based on the grid-independent analysis and verifying the rationality of numerical data, oil-gas movement mechanism and oil return characteristics for different scavenge offtakes are calculated and analyzed. Results show that both the ramp sump and eccentricity sump offtake structures have favorable effects on improving the local oil distribution such as recirculation and stripping, etc. at low rotation speeds and alleviating the rapid decline of scavenge efficiency at high rotation speeds. Meanwhile, the air shear force is the main reason for the rapid decline of scavenge efficiency, while the design of oil return sump makes for the oil discharge from the scavenge offtake, and the deeper the sump depth is, the better.

An Improved CFD-synthesis Method for Predicting Inlet Dynamic Distortion

Abstract This article presents an improved computational fluid dynamics (CFD)-synthesis method to predict dynamic distortion. A steady-state flow field is derived from a CFD solution, through which are acquired total pressure, density, turbulence kinetic energy and others in steady-state at an aerodynamic interface plane (AIP). Back-propagation artificial neural network (BP ANN) is used to find out the relationship between the measured flight turbulence and the CFD-computed turbulence parameters. The dynamic pressure is obtained by incorporating CFD-found total steady-state pressure with fluctuating pressure. Finally, the dynamic distortion is predicted by means of the synthesized dynamic pressure. The fairly good agreement between the computed inlet surface pressure and the flight test data bears out the reliability of CFD solution used in this article. To validate the proposed method, six sets of flight test data are used and the results show that the predicted dynamic distortion is well in line with the distortion displayed in flight tests. An examination of the traditional method is also accomplished and the comparison also shows that the proposed method is superior to the traditional one in higher consistency with flight test data.