Development and validation of a CFD based optimization procedure for the design of torque converter cascade

Proceedings of the Institution of Mechanical Engineers, Part D:

Yang

et al. 2020

Hydraulic torque converter is of lower efficiency in the powertrain, particularly at low speed ratio, which is crucial for vehicles due to its ability of torque multiplication. Therefore, torque converters should be taken into account with both higher start-up acceleration and transmission efficiency. Inspired by the fact that the multi-airfoils of the aircraft can improve the lift, a new design of segmented turbine blade in torque converter is presented to improve the transmission efficiency and start-up acceleration. To ensure reproducibility and popularization, the camber line and shape of blades are extracted to obtain the expression in the Cartesian coordinate system. A scale-resolving simulation setting, large eddy simulation with kinetic energy transport, and refined hexahedron meshes, which were verified by our studies, are applied to simulate the three-dimensional transient flow numerically. According to the results of computational fluid dynamics analysis, the new design eliminated the ultra-high vorticity of the near-wall boundary layer to reduce the flow loss, which further improves fuel economy. The pressure difference in the segmented turbine blade is significantly higher than that of the original model, causing the improvement of powertrain performance. As a result, the torque ratio and nominal torque increase by 6.7% and 7.7%, respectively, at stalling speed ratio; meanwhile, the maximum efficiency increases by 1.1%. This research, using a new design of segmented blades, has many advantages, such as high starting torque ratio, large adjusting range, and greater fuel economy, and shows great potential to apply in the manufacturing process.

Section: Introductionmentioning

confidence: 99%

Performance improvement and flow field investigation in hydraulic torque converter based on a new design of segmented blades

Proceedings of the Institution of Mechanical Engineers, Part D:

Yang

et al. 2020

“…The flow structure demonstrated that the instantaneous flow status of each blade was not identical, indicating that a simulation-based on periodic boundaries of a single passage has certain limitations for these devices. An important component of automatic transmissions (Liu et al, 2018b), HTC is comprised of three elements:…”

Section: Numerical Simulationmentioning

confidence: 99%

“…The HTC is crucial for whole vehicles due to its ability of torque multiplication, automatic adaptability and shock absorption (Li et al, 2019;You et al, 2018). Nonetheless, the fluid in the working chamber of HTC is driven by the rotating rotor and restricted by the blade wall, which leads to the rotation effect of the flow, and further complicates the development of turbulence (Liu et al, 2019(Liu et al, , 2018b. The prediction of dynamic performance and economics performance remains as a major challenge for the design.…”

Section: Introductionmentioning

confidence: 99%

Calculation and analysis of thermal flow field in hydrodynamic torque converter with a new developed stress-blended eddy simulation

Yang

et al. 2021

HFF

Purpose The flow phenomenon of particle image velocimetry has revealed the transition process of the complex multi-scale vortex between the boundary layer and mainstream region. Nonetheless, present computational fluid dynamics methods inadequately distinguish the discernable flows in detail. A multi-physical field coupling model, which was applied in rotor-stator fluid machinery (Umavathi, 2015; Syawitri et al., 2020), was put forward to ensure the identification of multi-scale vortexes and the improvement of performance prediction in torque converter. Design/methodology/approach A newly-developed multi-physical field simulation framework that coupled the scale-resolving simulation method with a dynamic modified viscosity coefficient was proposed to comparatively investigate the influence of energy exchange on thermal and flow characteristics and the description of the flow field in detail. Findings Regardless of whether quantitative or qualitative, its description ability on turbulence statistics, pressure-streamline, vortex structure and eddy viscosity ratio were visually experimentally and numerically analyzed. The results revealed that the modification of transmission medium viscous can identify flows more exactly between the viscous sublayer and outer boundary layer. Compared with RANS and large eddy simulation, a stress-blended eddy simulation model with a dynamic modified viscosity coefficient, which was further used to achieve blending on the stress level, can effectively solve the calculating problem of the transition region between the near-wall boundary layer and mainstream region. Research limitations/implications This indeed provides an excellent description of the transient flow field and vortex structure in different physical flow states. Furthermore, the experimental data has proven that the maximum error of the external performance prediction was less than 4%. Originality/value An improved model was applied to simulate and analyze the flow mechanism through the evolution of vortex structures in a working chamber, to deepen the designer with a fundamental understanding on how to reduce flow losses and flow non-uniformity in manufacturing.

“…This approach adopts the sample points selected by the orthogonal array design (OAD), and its spatial filling and equalization are not as good as the optimal Latin hypercube design (Opt LHD), so the error of prediction calculation is larger. 15 Liu et al 16,17 proposed a multi-objective optimization problem with the stall pump capacity factor λ B 0 and the K 0 as the objective function and 19 blade shape parameters as the independent variables. The Kriging method has great advantages in terms of accuracy and efficiency compared to the response surface methodology (RSM).…”

Section: Introductionmentioning

confidence: 99%

Multi-objective optimization of the cascade parameters of a torque converter based on CFD and a genetic algorithm

Ran

Proceedings of the Institution of Mechanical Engineers, Part D:

et al. 2021

It is hard to simultaneously improve the peak efficiency (η *) and the width of the high-efficiency region ( Gη) for a hydrodynamic torque converter. A combination of comprehensive CFD simulation and multi-objective optimization was pretested. The elaborate CFD simulation calculation included a reasonable mesh layout, a robust algorithm and a correct turbulence model, whose results were also experimentally verified. In our study, the Kriging surrogate model was first used to construct a nonlinear relationship between the inlet and outlet angle and the economic performance index of the hydrodynamic torque converter. To ensure that the accuracy of the surrogate model meet the requirements, we also used 10 sets of sample points to verify the accuracy of our surrogate model. The accuracy is found to meet the requirements, which shows that the accuracy of the constructed surrogate model is relatively high. We choose to apply the second-generation non-dominant sorting genetic algorithm (NSGA-II) to solve our problem. After solving the Pareto frontier solution set, we obtain a set of global optimal solutions on the Pareto frontier solution set. The optimization results show that the η * is increased by 2.49% and that the Gη is increased by 14.23%. We extracted the flow field structure near the turbine region, characterized the difference between original and optimal model from the flow field perspective, and demonstrated the accuracy of our optimization results. Finally, we used CFD to verify our optimization results, further illustrating the accuracy of the optimization results prediction. Literature research indicates that a large amount of experiments to optimize the η * and the Gη of the hydrodynamic torque converter will bring huge trial cost and time cost. We conclude from our research that the proposed calculation method can solve such problems well.