Qingdong Yan

Study on reconstruction and prediction methods of pressure field on blade surfaces for oil-filling process in a hydrodynamic retarder

Purpose – Traditional three-dimensional numerical methods require a long time for transient computational fluid dynamics simulation on oil-filling process of hydrodynamic braking. The purpose of this paper is to investigate reconstruction and prediction methods for the pressure field on blade surfaces to explore an accurate and rapid numerical method to solve transient internal flow in a hydrodynamic retarder. Design/methodology/approach – Dynamic braking performance for the oil-filling process was simulated and validated using experimental results. With the proper orthogonal decomposition (POD) method, the dominant modes of transient pressure distribution on blades were extracted using their spatio-temporal structural features from the knowledge of computed flow data. Pressure field on blades was reconstructed. Based on the approximate model (AM), transient pressure field on blades was predicted in combination with POD. The causes of reconstruction and prediction error were, respectively, analyzed. Findi...

Study on influence of inlet and outlet flow rates on oil pressures and braking torque in a hydrodynamic retarder

Purpose Traditional prediction of braking characteristics of vehicular hydrodynamic retarders is commonly conducted based on braking characteristics model of closed working chamber, namely, closed working chamber model (CWCM). In CWCM, inlet and outlet oil pressures and braking torque are considered to be independent of inlet and outlet flow rates. However, inlet and outlet flow rates can affect internal and external braking characteristics under actual working conditions. This study aims to establish a more accurate braking characteristics model of a hydrodynamic retarder under full oil-charging condition, and then the influence of varying inlet and outlet flow rates on oil pressures and braking torque is investigated in this paper. Design/methodology/approach A full flow passage of working chamber in a hydrodynamic retarder with inlet and outlets was established, and the reliability of numerical model was analyzed and validated. Pressure rise was introduced to describe the variation of inlet and outlet oil pressures. Then, on the basis of the validation, the CWCM was proposed at different rotor rotational speeds. The inlet and outlet oil pressures and braking torque were numerically computed at different inlet and outlet flow rates with Full Factorial Design experimental method. The results obtained were involved into establishing the braking characteristics model of open working chamber, namely, open working chamber model (OWCM), combined with Radial basis function approximation model. The OWCM with different inlet and outlet flow rates was analyzed and compared with CWCM. Findings The results show that inlet and outlet flow rates have obvious influence on the variation of inlet and outlet oil pressures in OWCM compared with CWCM. The outlet A pressure rise significantly changes with the inlet and outlet A flow rates, while the pressure rise of outlet B is mainly affected by the outlet B flow rate. Originality/value This paper presents an OWCM of hydrodynamic retarders under full oil-charging condition. The model takes into account the impact of oil inflowing and outflowing from the working chamber, which can provide a more accurate prediction of braking characteristics of hydrodynamic retarders.

Numerical Sensitivity Analysis of the Effect of Pump Outlet Radius on the Performance of Torque Converter

In order to study the influence of torque converter inlet and outlet radius, especially pump outlet radius, the traditional one-dimensional streamline theory and DOE were combined to analyze the parameter sensitivity. And the three-dimensional flow field simulation was adopted to validate the results of one-dimensional approach. The results showed that the pump outlet radius had a significant effect on stall torque ratio and pump torque coefficient. The pump torque coefficient increased and the stall torque ratio decreased with an increasing pump outlet radius. The sensitivity analysis results showed that the pump inlet radius had a great influence on the efficiency of torque converter. The results of both methods agreed well with each other and showed that the two methods were both effective. Decreasing pump outlet radius could reduce the pump load and increase stall torque ratio, and moreover, solve the problem of pump overload without much efficiency sacrifice.

Braking characteristics integrating open working chamber model and hydraulic control system model in a hydrodynamic retarder

Hydraulic control system has important influence on the steady and transient braking performance of a hydrodynamic retarder. The braking characteristics of hydrodynamic retarder regulated by hydraulic control system should be investigated first, before designing and making the braking strategy and control method. The accurate and detailed braking characteristics models of open working chamber and hydraulic control system are established, integrated, and validated by steady and dynamic experimental data. Based on full factorial design experimental method, the influence of control parameters on braking performance achieving steady state is analyzed with parameter sensitivity, and the effect of control parameters on braking response characteristics is conducted. Then the influence of different tube lengths between working chamber and hydraulic control system on braking performance is discussed and analyzed. The results show the control pressure and rotor rotational speed both have significant impact on braking characteristics with obvious nonlinear, coupling, and interaction effect. The longer response time of hydraulic control system will be for the larger braking torque. Shortening the tube lengths as much as possible is needed to improve the braking torque, cooling flow rate, and system integration.

Unsteady Simulation of a Synthetic Jet Actuator with Cylindrical Cavity Using a 3-D Lattice Boltzmann Method

A synthetic jet actuator is a zero-net mass-flux device that imparts momentum to its surroundings and has proved to be a useful active flow control device. Using the lattice Boltzmann method (LBM) with the Bhatnagar-Gross-Krook (BGK) collision models, a 3-D simulation of a synthetic jet with cylindrical cavity employing a sinusoidal velocity inlet boundary condition was conducted. The velocity distributions are illustrated and discussed, and the numerical results are validated against previous experimental data. The computed results show the ingestion and expulsion flow over one working cycle as well as the evolution of vortices important to the control of the separated shear layer. Zero-net mass-flux behavior is confirmed.

Numerical investigations of the flow induced oscillation of a torque converter

The flow induced oscillation of a three-element torque converter was investigated numerically under various operational conditions. A two-way coupling fluid–structure interaction simulation was performed using ANSYS-Fluent along with the ANSYS Transient Structural module. The fluid pressure excitation and the dynamic structure response were investigated at various turbine/pump rotation speed ratios . The maximum pressure blade load and structural deflections were observed in the stall condition, corresponding to the highest torque transmission ratio. The pressure pulsations and structure oscillations were monitored at locations selected on the basis of time-averaged distributions. The turbine oscillations were dominated by the frequency of pump blade passing at . The stator always oscillated under impact from the upstream flow with the dominating pump shaft frequency. Both the time-averaged and instantaneous features revealed that the pump oscillations were almost independent of SR.

Design of experiments to investigate blade geometric effects on the hydrodynamic performance of torque converters

Torque converters are key components in automatic and hydrodynamic transmissions. Power is transmitted through the reaction force of fluid on cascades; thus, the geometry of the blade is essential to torque converter performance. The traditional one-dimensional blade design approach becomes inefficient for modern torque converter design because torque converters are highly coupled turbomachines and the flow is three-dimensional. In the present research, a novel six-parameter blade camberline design was developed to describe the overall shape of the blade. A full two-level factorial design was conducted with computational fluid dynamics (CFD) simulations on each component to determine the sensitivity of design variables and investigate the relationship between design parameters and hydrodynamic performance. The design variables were reduced from 18 to nine after the screening design. A quarter-fractional factorial design was performed on the selected primary design variables to explore the first-order interaction effects between different wheels. Then a response surface was generated for each component to provide a substitution model for further optimization. A series of torque converters with various design parameters were fabricated and tested to validate the important effects determined in the design of experiments (DOE) process. It is found that CFD in combination with DOE is able to precisely capture the correlation between design variables and hydrodynamic performance. A base torque converter was optimized based on the DOE studies and the result was tested. Pronounced improvement in powertrain performance and fuel economy were observed.

Parametric Analysis and Optimization of Inlet Inflection Angle in Torque Converters

Torque converters are widely used in all means of transportations, such as cars, buses, trucks, and the list can go on. Since power is transmitted via fluid, the blade geometry which forms the flow passages is crucial to torque converter performance. The inlet deflection angle is an important blade design parameter with respect to both performance and manufacturability of torque converters. In the conventional design procedure, inlet deflection angle is often given by the designer’s experience or is selected based on experimental data if available. This study presents a method of optimizing the inlet deflection angle for torque converters and provides a series of non-inferior solutions for the decision maker to select from. The advantages of the method proposed consist of improved design quality and significantly shorter design cycle. A combination of computational analysis and global optimization algorithm was used in this study. A torque converter base model was evaluated using computational fluid dynamics for predicting its performance. The proper grid density and turbulence model were selected through correlation to the experimental data available. The following tasks were automated and integrated to form a parameterized design loop: 1) torque converter flow field CAD modeling, 2) meshing, and 3) CFD simulations and results post-processing. Selecting peak efficiency, stall torque ratio and stall pump capacity factor as objective functions, a multi-objective genetic algorithm was included in the design loop to optimize the torque converter performance.The CFD results proved to be in good agreement with the experimental data over the range of operating conditions considered in this study. The influence of inlet deflection angle on the performance of torque converter was determined through a parametric analysis and a series of Pareto-optimal solutions were determined by the optimization procedure, which proved to improve the performance of the base model torque converter.Copyright