Abstract
Keywords - Lap time optimisation, go-kart, driving line, gas dynamic engine simulation, aerodynamic CFD
Abstract - Competition go-karts must satisfy the philosophy of extreme simplicity, but their design can be even more complex than the one of standard vehicles. Karts until today have been developed mainly on the basis of experimental tests and personal experience of skilled technicians. However, the increasing technological content of these vehicles nowadays requires design and analysis criteria that are peculiar to modern engineering. Even if experimental tests are still the most common and extensively used approach, the numerical simulations has been developed so much in the latest years to become rapid and reliable. On one hand, this allows to support the experimentation, reducing the number of experimental test to be done; on the other, it produces a complete description of the physical quantities involved, permitting a deep understanding of real phenomena and behaviour. The success of a competition vehicle depends on several factors including vehicle dynamics, engine performances, and aerodynamic effects.
In this paper an integrated tool, addressed to lap time simulation of a competition go-kart, is presented. All the mentioned components of vehicle dynamics are taken into account. The aerodynamic performance of a go-kart is predicted by means of a CFD software that solves indirectly the equations for the continuum (Navier-Stokes) by reproducing the fluid dynamics at the molecular level. It has to be noted that aerodynamics effects act not only on the drag and lift forces but also on the engine heat transfer capability and on the dynamic load transfer. Subsequently the engine performance can be evaluated using a mono-dimensional fluid dynamic code that is able to simulate the whole engine, from air box to exhaust system, taking in account the most important engine parameters. Vehicle longitudinal and lateral dynamics was computed by means of a solver dedicated to competition go-kart dynamic analysis that is able to foresee the vehicle behaviour responding to driver commands. The numerical model was tuned in order to match a series of acquired track results.
A general purpose track model was then developed suitable for the representation of testing track or race circuits and able to manage an arbitrary path lying within its boundaries. It is then possible to simulate an arbitrary manoeuvre, collecting aerodynamic, engine and vehicle models results into the main simulation program, and taking advantage of the track model. Special manoeuvres like steering pad, double change of line and spiral trajectory and whole circuit lap have been considered. The entire tool is sensitive to aerodynamic, handling, engine and tires parameters and then is useful to find optimised design and set-up solutions. A practical application is presented about the global tuning of a go kart to minimise the lap time in an actual race track.