Hydraulic torque converters are prone to cavitation due to their high impeller rotational speeds and their complex three-dimensional flow characteristics. Since the blades are the core components of torque converters, the shapes of the blades are important to the hydraulic performance and cavitation characteristics. Different cavitation computational fluid dynamics (CFD) models for a torque converter were developed to simulate the internal cavitation flow for different pump and turbine blade exit angles, and the influence of the blade angles on the cavitation characteristics and cavitation flow field in the torque converter was investigated. Experimental prototypes were produced and tested for verification. The results indicate that the pump and turbine blade exit angles had significant effects on the cavitation number of the torque converter. Increasing the pump and turbine blade exit angles promotes the generation and intensification of cavitation, resulting in severe changes in the shapes and locations of the cavitation bubbles due to changes in the fluid impact angles. Additionally, cavitation is quickly suppressed and the performance is improved when the blade exit angles are reduced within an appropriate range, in particular, that of the turbine blade. These research results can provide guidance for the design of a high-performance hydraulic torque converter cascade system and the suppression of cavitation for practical engineering applications.

Cavitation is a transient phase transition between liquid and vapor, and it often occurs in fluid machinery, especially in a hydraulic torque converter that uses oil as the working medium to transmit speed and torque. The complex and strongly coupled fluid flow in the torque converter is prone to cavitation due to high rotating speed and high-temperature working conditions. Cavitation seriously affects the working performance, transmission smoothness, and service life of the torque converter. The flow pressure in the stator of a torque converter under various charging conditions and high rotating speeds was measured. The pressure data on the stator blade were analyzed in the time domain and frequency domain to identify and evaluate the cavitation characteristic. The transient cavitation flow inside the torque converter was also simulated with the computational fluid dynamics model. The results show that the shedding of cavitation seriously reduced the hydraulic performance, hindered the fluid flow, and destroyed the stability of the flow field. Moreover, cavitation aggravates the complexity and nonlinearity of the pressure frequency and hydraulic performance oscillation of the torque converter, and seriously affected the shaft/blade interaction frequency between the pump and stator. Meanwhile, the occurrence and degree of cavitation in the torque converter can be evaluated by A_PS.shaft/A_PS.blade (the amplitude ratio of the shaft interaction frequency and blade interaction frequency between pump and stator) with spectrum analysis of the dynamic pressure, and the critical value was 1.6 for the test torque converter. The research revealed the influence of cavitation on the internal flow field of the torque converter and provided a novel practical cavitation evaluation technique.

Hydraulic torque converter is widely used in transmission units as it is able to provide variable speed and torque ratio, isolate vibration, and absorb shock. The pursuit of a highly packed power unit requires a high capacity/speed torque converter, consequently resulting in a higher risk for cavitation and severe performance degradation, noise, vibration, and even failure. Existing cavitation models generally focus on water, and the empirical parameters are not suitable for the cavitation prediction of torque converter which utilizes high viscosity oil as its working medium. This paper focused on the influence of parameters on the performance and cavitation characteristics of torque converter. A full flow passage geometry and different computational fluid dynamics (CFD) models with cavitation were developed to predict torque converter fluid behavior by resolving Reynolds-averaged Navier–Stokes equations using finite volume method (FVM). The numerical results indicated that nuclei volume fraction, vaporization coefficient, mean nucleation site radius, and maximum density ratio have great influences on the cavitation behavior. These parameters altered the degree of cavitation and the pressure distribution on the surface of stator blades, and affected the stall performance such as stall capacity factor and torque ratio. The cavitation model was then modified to improve calculation accuracy. The test results showed that the prediction error under stall operating condition was decreased from 6.7% to 2%. This study provides insight on the influences of the empirical parameters on both internal cavitation behavior as well as overall hydrodynamic performance.

The integrated ducted structure significantly enhances the aerodynamic performance of the duct–rotor system, reducing noise and enhancing rotor safety. However, in the duct–rotor system, the coupled parameters of the rotor and the duct are crucial to its aerodynamic characteristics. This study employs a Computational Fluid Dynamics numerical analysis to investigate the aerodynamic performance of the duct–rotor, focusing on coupled parameters related to the rotor blade’s relative position and tip gap. Additionally, our research delves into the fundamental mechanisms of key coupled parameters, such as the blade tip gap, elucidating their role in optimizing the duct–rotor’s aerodynamics. The results emphasize the critical role of the tip gap in influencing the aerodynamic performance of the duct–rotor. Notably, when the tip gap exceeds 3.0% of the duct’s radius, the aerodynamic advantage provided by the duct is insufficient to offset the loss in the rotor’s performance. As the tip gap exceeds 7.0% of the duct’s radius, the aerodynamic deterioration caused by the duct gradually stabilizes. Furthermore, the influence of rotor blade position on aerodynamic performance is relatively minor. However, placing the rotor at the duct exit position proves advantageous for improving the aerodynamic distribution characteristics of the system.

The precise regulation of the hinge moment and pitch angle driven by the pitch-regulated mechanism is crucial for modulating thrust requirements and ensuring stable attitude control in Martian coaxial rotorcraft. Nonetheless, the aerodynamic hinge moment in rotorcraft presents time-dependent dynamic properties, posing significant challenges for accurate measurement and assessment for such characteristics. In this study, we delve into the detailed aerodynamic hinge moment characteristics associated with the pitch-regulated mechanism of Mars rotorcraft under a spectrum of control strategies. A robust computational fluid dynamics model was developed to simulate the rotor’s aerodynamic loads, accompanied by a quantitative hinge moment characterization that takes into account the effects of varying rotor speeds and pitch angles. Our investigation yielded a thorough understanding of the interplay between aerodynamic load behavior and rotor surface pressure distributions, leading to the creation of an empirical mapping model for hinge moments. To validate our findings, we engineered a specialized test apparatus capable of measuring the hinge moments of the pitch-regulated mechanism, facilitating empirical assessments under replicated atmospheric conditions of both Earth and Mars. The result indicates aerodynamic hinge moments depend nonlinearly on rotational speed, peaking at a 0° pitch angle and showing minimal sensitivity to pitch under 0°. Above 0°, hinge moments decrease, reaching a minimum at 15° before rising again. Simulation and experimental comparisons demonstrate that under Earth conditions, the aerodynamic performance and hinge moment errors are within 8.54% and 24.90%, respectively. For Mars conditions, errors remain below 11.62%, proving the CFD model’s reliability. This supports its application in the design and optimization of Mars rotorcraft systems, enhancing their flight control through the accurate prediction of aerodynamic hinge moments across various pitch angles and speeds.