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In order to study the complex transient flow characteristics of a high-pressure aero-fuel centrifugal pump within its full working envelope, a certain type of centrifugal pump is numerically simulated, in which the simulation results are compared with the experiment results to verify the effectiveness of the present simulation method. Then, the verified simulation method is selected to analyze the transient flow characteristics, in which the time-frequency characteristic of pressure pulsation at monitored positions is analyzed by using fast fourier transform. In addition, the unsteady flow structures are studied by focusing on the relative speed, turbulent kinetic energy and so on. The results show that the main frequency of pressure pulsation in the impeller and volute is rotation frequency and blade frequency, respectively, where different monitoring points show similar trend. Meanwhile, the flow is relatively stable under design flow rate condition. However, a certain large-scale vortex appears in the impeller channel under small flow rate conditions, which mainly exists at the exit of the impeller channel near the tongue. In addition, turbulent kinetic energy at the exit of the impeller and the tongue has a large distribution range and changes seriously, where a certain hydraulic loss is produced.

Black ice is an ice layer formed by freezing rain or accumulated water on the asphalt pavement surface in cold weather. This ice layer completely shields the texture structure of the pavement and destroys the original microstructure. The direct contact between the automobile tire and the ice surface leads to a sharp decrease in the adhesion coefficient, so the automobile is prone to lateral instability on the icy pavement. In this paper, the simulation model of the icy pavement is established in Matlab/Simulink to verify the control effect of the lateral stability controller based on the Electronic Stability Program under two steering limit conditions. The results show that the vehicle without a lateral stability controller will lose stability and sideslip even when it is steering at low speed on the icy pavement, and the lateral stability controller can effectively control the yaw rate of the vehicle when it is steering, which greatly reduces the offset of the sideslip angle of the centroid and inhibits the lateral acceleration exceeding the ice surface limit, which improves the maneuverability and stability of the vehicle under the freezing limit condition. The application of the controller is of great significance to improve the driving safety of the regional asphalt pavement. Due to the low adhesion coefficient of the icy pavement and the limited braking force and additional yaw moment of the tire provided by the adhesion force, the vehicle with a lateral stability controller is still likely to lose stability under the critical condition of medium or high-speed single shift line., Author(s): Yunsheng Zhu [1]; Huacong Li [1]; Kaifeng Wang (corresponding author) [1]; Yunhan Bao [2]; Peng Zeng [3] 1. Introduction In the cold climate, pavement freezing often occurs in the [...]

A high-speed centrifugal pump is the key facility to deliver oil in an aero-engine. The stable operation is quite important to the safety of the engine. High-speed pump stability is essentially caused by the transient pressure pulsations excited by the complex flow within the pump, which needs to be clarified, especially for the pump under a rotating stall condition. In the current research, unsteady pressure pulsation and the corresponding flow distribution of the high-speed centrifugal pump are analyzed using the delayed detached-eddy simulation (DDES) method. Pressure signals within the pump are extracted by monitoring points. Results show that the dominant components in the pressure spectrum exhibit a significant difference at various flow rates, which locates at the blade passing frequency fBPF under the rated working condition and deviates to five times the shaft frequency (5fn) at the stalled condition. Such phenomenon is not observed in the normal centrifugal pump with low speed when using numerical and experiment methods, and usually the amplitude at fBPF reaches the maximum. Under the stalled condition, the component at 0.2fn is generated and considered as the rotating stall frequency, which is the same at different stalled flow rates. From velocity distribution, it is found that several blade channels are stalled as characterized by the large-scale separation bubbles, which are induced and triggered by the volute tongue. [ABSTRACT FROM AUTHOR]

In this paper, a model reference adaptive sliding mode control method is proposed for a variable cycle engine (VCE) which is a MIMO system with uncertainties and external disturbances. The reference model is designed based on optimal LQR method to provide ideal reference states. An adaptive sliding mode controller (ASMC) is designed for model reference adaptive control structure, which the adaptive law is derived based on Lyapunov function to estimate the unknown upper bound of uncertainties and external disturbances. Simulation results for VCE demonstrate the performance and fidelity of the proposed method. [ABSTRACT FROM AUTHOR]