Undertray Design and Development Procedure with CFD : An Optimization Study of Different UndertrayDesigns with CFD Computations

Sammanfattning: Race car aerodynamics has played a vital part to improve lap times over the years of motor racing. Having good road adhesion with slick tires and aerodynamic downforce will increase the vehicles maximum lateral force and thus higher cornering speeds can be achieved. The undertray and diffuser is the most efficient aerodynamic component on most racing vehicles and is capable of producing six times more downforce than its contribution to drag plus, if optimized correctly, able to significantly reduce the vehicle's drag coefficient. The intent of this project is to optimize a completely unique undertray design for the KTH Formula Student teams racing vehicle DeV17. The undertray is inspired by the Aston Martin Valkyrie venturi tunnel design and is optimized by iterative change in CAD design parameters for three different chassis designs. The results are obtained with CFD RANS simulations using the k-ω (SST) turbulence model with the Siemens Star-CCM+software. The optimum design gave 530 N and 90 N of downforce and drag respectively at a velocity of 80km/h. The venturi tunnel design is proven to give a 29% downforce improvement over a conventional flat plate design with stronger longitudainal vortices and lower, more widespread, minimum pressure distribution. The most important aspects that affect downforce in undertray design is concluded to be a diffuser outlet height, upsweep and vehicle ground clearance. No specific aerodynamic advantages in having a convergent tapering of the tunnel cross-section is observed, meaning the undertray can be represented as only consisting of an expanding diffuser. The tunnel design is considered to give promising track testing results and be a spark for further innovative ideas with aerodynamic design for both the automotive and racing industry.