The present work is dedicated to the modeling and simulation of the radar signature of raindrops within wake vortices. This is achieved through the computation of the equation of raindrop motion within the wake vortex flow. Based on the inhomogeneous distribution of raindrops within wake vortices, the radar echo model is computed for raindrops in a given resolution cell. Simulated Doppler radar signatures of raindrops within wake vortices are shown to be a potential criterion for identifying wake vortex hazards in air traffic control. The dependence of the radar signature on various parameters, including the radial resolution and antenna elevation angle, is also analyzed.

Served as a core component, the performance of the hydraulic transformer (HT) directly affects the energy-saving performance of the Common Pressure Rail (CPR) system. The pressure reduction process of HT is accompanied by an expansion of the plunger cavity, which can result in steeply pressure drop and lead to cavitation under certain working parameters. In order to enhance the performance, a double rotor hydraulic transformer (DRHT) is proposed, and a systematic analysis of the pressure reduction process in DRHT is provided by CFD simulation and experimental test. The CFD model is based on the dynamic mesh method considering both cavitation and turbulence. The experiment is carried on with a special designed prototype and four kinds of valve plates. The results show that the transient pressure decreases sharply with increasing rotating speed, and a minimum transient pressure is reached at the control angle of -30 degrees. The damping groove can deter the volume expansion effect and thus enlarging the working range, but the volume loss will be incurred. The results of the parameter study show that the damping groove with the length 4 mm and the depth 3 mm can avoid the excessively low transient pressure occur while maintaining low volume loss. The simulation curves have good consistency with the test results, which credit the numerical method feasible and effective. The current work is also significant for further design and the application of the DRHT.

The hydraulic transformer is the core component when it works with the common pressure rail system, which integrates the functions of the pump and the motor, and thus possesses sensitive pressure characteristics. The rotating speed has significant influence on the pressure characteristics of a hydraulic transformer while it has not been considered previously. In this study, aimed at improving the working performance, a novel double rotor hydraulic transformer is proposed and a comprehensive mathematical model considering the dynamic characteristics of the cylinder block is established. At the same time, a prototype is made and the experiment is conducted. The test results show that the robust rotor structure enables a larger pressure range, and the numerical results exhibit a good match with the test results. The parameter sensitivity study shows that the delivery pressure is mainly subject to the valve plate control angle δ and, under the effects of the resistance torques, pressure loss will occur especially under a large control angle and a high rotating speed. The magnitude of the instantaneous angular velocity fluctuation increases sharply when the speed is lower than 400 r/min, which is the main reason for the serious pressure pulsation at a low speed. As a result of the improved low-speed stability and output flow uniformity, the pressure pulsation rate of the double rotor hydraulic transformer is greatly reduced. However, the pulsation rate is still high at an extremely low speed. In addition, when the rotating speed exceeds the capability of the damping grooves, the pressure undershoot becomes serious at the A-T transition region around the control angle of −30°. Consequently, from the perspective of pressure characteristics, the limitation on the rotating speed under small control angles is suggested for the design of the double rotor hydraulic transformer controller.

Serving as a core component, the performance of the hydraulic transformer (HT) directly affects the energy-saving performance of the common pressure rail (CPR) system. The HT is capable of both amplifying and reducing pressure without throttle loss, in which the pressure ratio is a critical parameter controlled through adjusting the torques acting on the rotors. However, our understanding of it relies on simplified models due to the complicated operation mechanism. This study focuses on the pressure ratio characteristics of the novel double rotor hydraulic transformer (DRHT). Firstly, the key influencing factors of the DRHT are acquired through theoretical analysis. Secondly, a dynamic model of the DRHT is established allowing for mechanical and fluid properties. Thirdly, a specially designed DRHT prototype is manufactured and the test bench is built up to verify the model. The experimental and numerical results show that the pressure ratio varies nonlinearly with the control angle especially when the control angle is greater than 10 degrees, while it changes almost linearly with the increasing rotating speed. The test results are consistent with the simulation results, which credit the mathematical model feasible and effective. The parametric study show that the augment of the A slot wrap angle on the valve plate could enhance the driving torque, as a result larger pressure ratio can be acquired. The enlargement of the B slot on the valve plate could make the variation of the pressure ratio more linearly. The current work is also significant for further design and the application of the DRHT.

With the development of human society, the concept of “carbon neutrality” has gradually attracted people’s attention. However, due to the existence of throttling loss, the efficiency of the hydraulic systems widely used is usually lower than 30%. In order to improve the energy conversion rate of the inefficient hydraulic system, a new type of multi-pump and multi-motor (MPMM) driving system is proposed, which can meet the flow and pressure requirements of different working conditions by switching the operation modes. In this paper, a functional symbol representation method of MPMM is specified and a systematic method of how to determine the operation mode of MPMM driving system is presented, which lays the foundation for the design of a new MPMM driving system. The test bench is built up and the correctness of the MPMM principle is verified. In addition, the comparative study of the conventional and the novel system is conducted. The results show that the input power of the hydraulic system adopting MPMM can be significantly reduced.