Looking "backwards" will soon become increasingly necessary for aerodynamics’ engineers and simulation specialists. In this case, it's about the industry's interest in abandoning exterior rearview mirrors in favor of small cameras, partly to reduce the vehicle's coefficient of drag (Cd) for improved fuel efficiency and also to enhance safety systems to provide a wide-angle view around and behind a vehicle.
A key element of that is ensuring the clearest vision possible in a wide span of road conditions, including those that would create camera lens soiling. Visualization and simulation software specialist Exa Corp.’s teams are now focusing on this vital and sometimes overlooked aspect of ADAS (advanced driver assistance systems) development and integration. After all, users are hardly likely to carry a chamois cloth to wipe mirror glass or onboard sensors clean.
Exa’s Executive Vice President, Ales Alajbegovic, explains the alternatives: “Design iterations with various underbody components, aerodynamic devices and shape factors can be used to find the best balance between aerodynamics and [sensor] soiling performance. They can dramatically alter the wake location and motion, and influence the trajectory, of rain particles which could interfere with cameras.”
Simulating the lifecycle of raindrops
Cameras have been seen as obvious replacements for hefty fender or door-mounted mirrors for many years, but their development and acceptance (for safety reasons) path has been extremely difficult. The ultra-low-volume (250 units) Volkswagen XL1 demonstrated that rear-view cameras could meet requirements. In testing an XL1 during its 2014 debut the author found them surprisingly acceptable in both city traffic and high speed motorway scenarios in Europe.
At Exa, where extensive vehicle anti-soiling work (snow, water and dirt) is underway using its PowerFLOW software to help keep the vehicle's greenhouse clear for maximum visibility, the likelihood of conventional exterior mirrors becoming obsolete is being taken seriously.
Said Alajbegovic: “Firstly, cameras should be placed in areas that are not exposed directly to large raindrops and rivulets on the surface of their surface. PowerFLOW simulates the lifecycle of raindrops as they approach the vehicle, break up due to the aerodynamic flow field, splash on the surface, are entrained into the vehicle wake, and are deposited on the vehicle’s surfaces.”
Cut lines and other features could be added to a vehicle’s surface to control water film motion. “We see this a lot today on mirror housings,” he explained.
Already some solutions exist for keeping exterior rearview cameras clean, including using a jet of water followed by a puff of air. But this type can be avoided, Alajbegovic noted through earlier design improvements "using more simulation and concurrent evaluation of aerodynamics and soiling at each design stage of a vehicle.”
As for the application of PowerFLOW to assess hydrophobic and hydrophilic coatings on cameras and sensors to assess their ability to keep a camera lens clean, Alajbegovic confirms: “This capability is still under development.”
Gaining more accuracy
Digital anti-soiling simulation work will be particularly significant in the upcoming world of sensor-controlled fully autonomous vehicles. The prospect of exponential test requirements are costly and time consuming. But it is not just futuristic vision systems to which Exa is applying PowerFLOW’s capability. It is also used to achieve better management of contaminants on the surface and in the air, on and around a whole vehicle.
As previously reported by Automotive Engineering (http://articles.sae.org/15034/), Land Rover used it during development of the 2017 Discovery. Engineers ran over 1000 simulations to better manage dirt and water management, obviating the need to use sometimes limited capability climatic wind tunnels. Exa’s highly repeatable particle simulations can be combined with real world predictions by including realistic wind conditions in simulations including turbulence caused by traffic, states the company.
The work generates a more accurate prediction of the level of soiling and spray patterns experienced in a vehicle’s daily use.
Exa has just launched its new PowerFLOW 5.4 software, designed to further improve real-world accuracy and the digital simulation process. The robust release "will enable engineers to predict even more accurately how new vehicle designs will perform and interact with their environments," said Senior Vice President and marketing boss Suresh Sundaram. It will also help keep vehicle sensors clean for safe, autonomous driving "and understanding the effects of variable road conditions on vehicle performance, fuel efficiency and range.”
Simulating sprayer coverage
During an initial assessment, and cross-correlation exercises between simulation and experiment, BMW was able to verify the potential and robustness of the Exa PowerFLOW water management capabilities in relation to windscreen sprayer modules, reveals the company. The sprayer modules are provided by suppliers to BMW and functional targets are set for the installation configuration on the series vehicle. The targets for the sprayer operation are subject to numerous vehicle aerodynamic considerations.
BMW simulation specialist Holger Gau, noted: “We have worked with the Exa PowerFLOW water management application to assess its potential in the BMW engineering cycles, and to develop a process where, given the sprayer properties, simulation can predict the sprayer coverage over the entire operating range of the vehicle. We see growing requirements for water management simulation applications."
Gau said BMW expects that future simulation may address topics such as side window soiling, backlight visibility and others.