Numerical investigation of road simulation in model scale wind tunnel

Abstract

The legislature is imposing ever stricter limits on emissions for the automotive industry. Added to this are the new test cycles RDE and WLTC, which exert even more pressure to reach the provisions and force the manufacturer to optimize every component on the vehicle. This also includes, in particular, the aerodynamics of the vehicles. If the proportion of aerodynamics in total consumption was already significant in the NEDC, it gained further weight in the new cycles due to the higher average speeds. This leads to the fact that the engineers have to be able to rely on development tools which are of high precision.

The wind tunnel has always been the development tool of aerodynamic engineers. Its structure and its effects have already been studied in several studies [1]. However, the studies were often limited given by the measuring technology. For some years now, another tool has been added, the CFD [2, 3]. It allows the user to carry out investigations under the most demanding conditions. Also, the CFD makes it possible to carry out the numerous optimizations that have become necessary in today’s development. In addition, a further possibility of flow testing has recently been added with the PIV measurement technology.

In this work, it is now possible to combine the advantages of all these development tools and thus to make detailed comparisons. The aim is to take a closer look at the impact of road simulation in the wind tunnel. For this purpose, the first test is to determine whether the simulation achieves a sufficient accuracy in order to be able to represent the flow phenomena. This includes the pressure profile in the measuring section as a general boundary condition and in the compartment the flow around the wheels. Subsequently, the individual elements of the road simulations will be discussed. In particular, the influence of the gaps on the wheel rotation units are the focus.

The preliminary examinations were successfully completed and the interesting phenomena were presented. For this, the pressure profile of the wind tunnel without a vehicle was compared to the measurement. After that the flow topology around the wheels and in the wake of the vehicle was opposed to a PIV measurement. Subsequently, three different road simulations were compared in the wind tunnel using the CFD. Once the road simulation was presented in detail with all gaps and measuring instruments, the 5- band two-dimensional without a column and a single-band system. The comparison showed a great influence on the lower vortex of the wheels and then the inflow of the rear wheels and the wake of the vehicle. In summary, it can be said that with higher resolution of the road simulation the vehicle resistance increases.