A Simplified Computational Fluid Dynamics Approach for Optimizing a Continuously Variable Transmission Casing

The Continuously Variable Transmission (CVT) is a popular form of automotive transmission that uses friction between a belt and pulley to transmit power. Due to the sliding and other losses associated with the belt, power is lost in the form of heat, which must be dissipated to enhance the belt’s life. The task of heat dissipation is, however, complicated by the use of a CVT casing, which serves to protect the transmission from mud, debris, etc. Consequently, the design of an optimum CVT casing for efficient cooling is a challenging task. Experimental approaches or 3D numerical simulation approaches to tackling such problems are either involved or time-consuming or both. This article discusses a novel and simplified strategy for optimizing a CVT casing for maximum heat removal, using computational fluid dynamics (CFD). The rotating pulleys are approximated as heated, rotating cylinders inside a two-dimensional flow domain of the casing. Transient CFD calculations are carried out on a practical CVT configuration in Ansys® Fluent, using the Shear Stress Transport k-ω turbulence model, for a total of nine different geometrical configurations. The effectiveness of a configuration is judged based on the surface heat flux from the pulleys. The practicality of the proposed approach is verified by a systematic comparison with three-dimensional simulations. It is observed that the simplified two-dimensional methodology can effectively supplant extensive three-dimensional simulations for determining the best CVT casing configuration. The novelty of this study is an emphasis on CVT casing optimization and in the reductionist nature of the simulations which allows for time-efficient transient simulations and simulating the boundary layers effectively. Transient boundary-layer simulations are computationally intensive for 3D simulations and have been neglected in the existing literature. The methodology proposed in this article also aims to provide grounds for further fluid flow research specific to the domain of cooling of continuously variable transmissions.