In this work, a combined numerical/experimental analysis is performed for an automotive tyre. A preliminary experimental activity is realized on examined tyre to measure the temperatures of its layers under various operating conditions. In a second stage, a 3D CFD model of tyre is developed in a commercial code and steady RANS simulations are performed in the full range of angular velocity with the aim to refine the prediction of convective thermal power and heat transfer coefficient. CFD simulation results are passed to a user-defined 3D thermodynamic model to furnish a detailed and reliable tyre thermal output with the advantage of a low computational time. Tyre thermodynamic model, enhanced by CFD-related thermal characteristics, demonstrates the capability to properly forecast the measured temperature of tyre layers in a wide range of investigated operating conditions. The proposed numerical approach represents a valuable tool supporting the optimization of tyre behavior and the development of advanced control rules for optimal tyre management.

RANS 3D CFD simulations to enhance the thermal prediction of tyre thermodynamic model: A hierarchical approach

Some general observations relating to tyre shear forces and road surfaces are followed by more specific considerations from circuit racing. The discussion then focuses on the mechanics of rubber friction. The classical experiments of Grosch are outlined and the interpretations that can be put on them are discussed. The interpretations involve rubber viscoelasticity, so that the vibration properties of rubber need to be considered. Adhesion and deformation mechanisms for energy dissipation at the interface between rubber and road and in the rubber itself are highlighted. The enquiry is concentrated on energy loss by deformation or hysteresis subsequently. Perssonrs deformation theory is outlined and the material properties necessary to apply the theory to Groschrs experiments are discussed. Predictions of the friction coefficient relating to one particular rubber compound and a rough surface are made using the theory and these are compared with the appropriate results from Grosch. The extent of the agreement between theory and experiment is discussed. It is concluded that there is value in the theory but that it is far from complete. There is considerable scope for further research on the mechanics of rubber friction.

Circuit racing, track texture, temperature and rubber friction

In order to improve the aerodynamic performance and optimization efficiency while wheel lightweight designing, a multi-objective optimization design method of wheel lightweight based on entropy weighted grey relational analysis (EGRA) was proposed in this article. The aerodynamic analysis finite element model of the assembled wheel was established, and the simulation accuracy was verified by experiments. Study the distribution law of performance parameters such as pressure and turbulent kinetic energy in flow field of the car, analyze the variation law of flow field velocity and turbulent intensity in front and rear wheel cavities of the assembled wheel, and analyze the cloud diagram distribution of temperature and surface convective heat transfer coefficient of the brake disc (<inline-formula> <tex-math notation="LaTeX">$h_{c}$ </tex-math></inline-formula>). Research on the influence of wheels with different disc structures on the aerodynamic drag coefficient of the car (<inline-formula> <tex-math notation="LaTeX">$C_{d}$ </tex-math></inline-formula>) and the <inline-formula> <tex-math notation="LaTeX">$h_{c}$ </tex-math></inline-formula>. Combined with grey relational analysis (GRA) and EGRA, the objective evaluation of the comprehensive aerodynamic performance of wheels with different disc structures was given. With the design of experiments (DOEs), 12 important design variables were screened out by contribution analysis method. Using the approximate model method, combined with the RBF surrogate model, a hybrid method combining EGRA and Non-Dominated Sorting Genetic Algorithm-II (NSGA- II) was proposed to lightweight and multi-objective optimize the assembled wheel. Comparing and analyzing the optimization platform recommending scheme, the technique for ordering preferences by similarity to ideal solution (TOPSIS) method preferring scheme and the EGRA method optimum scheme, it was found that the optimal compromise scheme was obtained by the EGRA method, the reduction of the <inline-formula> <tex-math notation="LaTeX">$C_{d}$ </tex-math></inline-formula> was more obvious, and the improvement rates of performance were also more balanced. After multi-objective optimization, the mass of the assembled wheel was reduced by 10.83%, the <inline-formula> <tex-math notation="LaTeX">$C_{d}$ </tex-math></inline-formula> was reduced by 5.02%, and the average convective heat transfer coefficient of brake disc (<inline-formula> <tex-math notation="LaTeX">$h_{a}$ </tex-math></inline-formula>) was reduced by 8.02%. The optimized assembled wheel has a weight reduction of 32.74% compared with the same type of cast aluminum alloy wheel, which has a remarkable lightweight effect and significant reduction on the <inline-formula> <tex-math notation="LaTeX">$C_{d}$ </tex-math></inline-formula>.

https://ieeexplore.ieee.org/ielx7/6287639/6514899/09870790.pdf

Study on Aerodynamic Performance and Lightweight Multiobjective Optimization Design of Wheel With Entropy Weighted Grey Relational Analysis Methods

Virtual 7-Post Rig: A 7 DoF Vehicle Model for Suspensions Parameters Optimization

Abstract To address the problems of severe heat generation and poor stability of traditional electromagnetic friction brakes, combined electromagnetic friction and shape memory alloy (SMA) braking method is proposed. This novel brake solves the traditional electric brake thermal decay problem based on the temperature sensing ability of SMA, which improves its working stability in a high-temperature environment. Based on Ampere’s law of magnetic field, the relationship between current and electromagnetic force was established, and the equation of electromagnetic force braking torque was derived. Based on the thermodynamic model of a SMA, the relationship between the frictional torque of SMA and parameters such as temperature, squeezing pressure, and structure size was established. The magnetic and thermal fields of this brake were analyzed by the finite element method to obtain the magnetic field distribution and the magnitude of electromagnetic force at different currents and to derive the temperature distribution of the brake at different currents. The brake was analyzed by the SMA squeezing pressure test platform and the braking performance test platform. The results show that the electromagnetic torque grows non-linearly with temperature, and the squeezing force generated by the SMA spring increases with temperature. When the current is 0.7 A, the braking torque generated by electromagnetism is 170.3 N m, while the maximum braking torque generated by the combination of electromagnetism and SMA is 212.6 N m, which is 20.4% higher than that of the traditional electromagnetic friction brake. This novel brake improves braking performance and ensures stable braking performance under temperature rise. 

Analysis of electromagnetic-thermal coupling braking properties of combined electromagnetic friction and shape memory alloy brake

The characterization and reproduction of tyre behaviour for vehicle modelling is a topic of particular interest both for real-time driver in the loop simulations and for offline performance optimization algorithms. Since the accuracy of the tyre forces and moments can be achieved by the accurate physical modelling of all the phenomena concerning the tyre-road interaction, the link between the tyre thermal state and the tyre frictional performance turns into a crucial factor. An integrated numerical methodology, allowing to couple the full 3D CFD (Computational Fluid Dynamics) flux within the internal chamber of the tyre with an equivalent discrete 3D structure model, is proposed with the aim to completely represent the tyre thermodynamic convective behaviour in the steady-state operating conditions. 3D CFD model enables the evaluation of the internal distribution of the gas temperature and of the thermal powers exchanged at each sub-wall in detail. This allows to increase the reliability of the tyre thermodynamic modelling with a particular reference to the proper managing of the aero-thermal flow of the brake disc impact on the rim temperature and therefore on the internal gas dynamics in terms of temperature and pressure, being able to optimize the tyre overall dynamic performance in both warm-up and stabilized thermal conditions. The steady RANS (Reynolds Averaged Navier–Stokes) simulations have been performed employing the 3D CFD model in a wide range of angular velocities with the aim to calculate the convective thermal flux distributions upon rim and inner liner surfaces. The simulation results have been then exploited to derive the convective heat transfer coefficients per each sub domain to be employed within the real-time tyre physical thermal model, with the peculiar advantage of an enhanced model reliability for thermal characteristics. To validate the proposed methodology, the tyre thermal model outputs, in terms of temperatures of internal and external layers, have been validated towards the acquired ones within the specific routine performed on tyre force and moment test bench, confirming an excellent agreement with the experimental data in the entire range of operating conditions explored.

/pdf/a-numerical-methodology-for-thermo-fluid-dynamic-modelling-52ik7i1tks.pdf

Giuseppe Alferi

Papers

A numerical methodology for thermo-fluid dynamic modelling of tyre inner chamber: towards real time applications