Evaluating Aerodynamic Performance and Particle Dynamics in a New Climatic Wind Tunnel using CFD

Sammanfattning

Contaminants such as dirt, mud, snow and rain can impair driver visibility and sensor functionality making driving in adverse weather conditions a safety concern. This study focuses on rain contamination of a passenger vehicle in three different wind tunnels at Volvo Cars: an aerodynamic wind tunnel with slotted walls, an old climatic wind tunnel, and a new climatic wind tunnel, both with open jet layouts. The research aims to investigate their airflow and particle transport properties to understand the unique characteristics of each tunnel and their suitability for specific applications. The investigation is conducted through CFD simulations of the wind tunnels, examining the airflow and particle dynamics in the empty test sections first, and then with a test vehicle. The findings highlight a different sensitivity of each tunnel to boundary interference, such as blockage effects and horizontal buoyancy. The more sensitive a wind tunnel is to such effects, the more the flow field will differ from open road driving and consequently the way the particles are transported. The results indicate that the aerodynamic wind tunnel closely replicates open road conditions, providing reliable drag measurements and acts as a baseline for soiling pattern. The old climatic wind tunnel shows significant flow acceleration and over-expansion due to its smaller nozzle and the vehicle being very close to it, which makes it too sensitive to blockage effects leading to inaccurate force measurements and peculiar soiling patterns due to the shear layer influence. The new climatic wind tunnel demonstrates a more moderate sensitivity to boundary interference effects, with a wider nozzle and increased distance to the vehicle, offering a balanced approach for both aerodynamic and contamination testing. In summary each wind tunnel provides different vehicle soiling patterns that could be more or less realistic to the driving scenarios of the customers. This research provides valuable insights into the design and optimization of wind tunnels for automotive testing. It emphasizes the importance of considering boundary interference effects in different wind tunnel layouts and underlines how fundamental it is to clearly outline the specific goals of different tests as their relevance could be questioned. The findings contribute to the development of safer vehicles by proposing multiple testing conditions.