<p>LIDAR sensors are a critical component of autonomous vehicles; however, their performance can be negatively affected during wet weather conditions. When rain droplets impact the LIDAR cover, the droplets can either stay attached or become separated from the cover depending on air-liquid flow conditions. Droplet shedding due to adjacent air shear stress occurs when the shear force on the droplet overcomes the droplet adhesion forces, which is a function of surface wettability, liquid droplet volume, and liquid surface tension. Although the impact of adverse weather conditions on these sensors has been studied extensively in recent years, there has been little advancement in developing a dewetting mechanism to keep the LIDAR cover dry. Droplets may coalesce and form a liquid film on the LIDAR cover in heavy rain conditions, driven by gravitational force, drag, and shear stress due to the airflow interaction. The LIDAR cover has been modified aerodynamically to enhance droplet detachment from the cover surface in this study. Five different aerodynamics cover designs have been proposed. For all the cover models, the front side of the cover is a cylindrical geometry with a radius of 25mm and 100 mm height with a wedge-shaped back section with angles 15º, 30º, 45º, and 90º, respectively. A wind tunnel with a 15.24 cm x 15.4 cm cross-section with a station for mist formation was used to simulate the wet weather conditions on the LIDAR cover. The wind tunnel is a blow-down type with a fan located upstream of both the mist and test sections to ensure water droplets will not damage the fan's blades. Two wind speeds were used, 12.7 and 22.8 m/s, and the mist station flow rate was selected to be 8x10<sup>-3</sup> kg/s. The test specimens were located at a 15 cm distance from the mist station nozzle inside the wind tunnel. The proposed front cover design can affect the air momentum at the solid-air interface, strengthening both liquid film inertia and instabilities before reaching the expanding corner at the rear surface. The force imbalance on liquid film can result in liquid detachment from the liquid film surface. Image analysis was used to evaluate the liquid impingement on the wall surfaces. Additionally, a numerical simulation shows the contour pressure, streamlines,&nbsp; shear stress on the cover at the different airspeeds.&nbsp; The numerical data display the effect of the separation flow of the proposed design on the LIDAR sensor. The experimental results revealed that the airspeed and cover geometry could influence the liquid film displacement on the LiDAR surface.</p>

Aerodynamic Design of Lidar Sensor Covers to Improve Its Performance Under Adverse Weather Conditions

Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2021/volume/85543

ASME 2021 International Mechanical Engineering Congress and Exposition (IMECE2021)

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