EAGER: CFD-based Adjoint Methods for Design Applications with Unsteady Separated Flows

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A computational method called adjoint based optimization is used in vehicle design to find optimal shapes for desired performance, such enhanced lift or reduced drag of aerodynamic shapes. Historically, this method has been used on streamlined shapes in simple flow fields, but more recently it has been applied to more complex shapes such as automobiles in complex, turbulent flow fields. However, the accuracy of the flow simulations and the effectiveness of the design process are unclear. An application where the accuracy of aerodynamic optimization is critical is the Winter Olympic sport of Luge. History has shown that Olympic medals have been determined by time differences of only a few thousandths of a second. The aerodynamics are complicated because the geometry itself is complex and the flow behind the rider/sled involves large scale unsteady turbulent motion (similar to a vehicle). Traditionally luge equipment has been developed by former athletes and was hand shaped based on hunches, feel, and experience. The flow conditions, and historic lack of science based design optimization, make luge sleds an ideal choice for investigation of the effectiveness of adjoint based optimization to perform aerodynamic optimization The successful design, build, and experimentally validating adjoint designs for unsteady flows in this project can potentially have a significant benefit to future designs of cars/trucks, boat/ships, and advanced air vehicles for drag minimization, increased performance during turns/maneuvering, or the prevention of flow separation while accelerating/decelerating.The goal of this work is to investigate the effectiveness of adjoint methods to reach an optimal shape in turbulent, unsteady, separated flows using experimental validation. An adjoint based method will be developed and applied to a luge sled/rider model that targets modification of the sled shape to minimize drag. Experimental testing will be performed to provide performance data of the intermediate shapes throughout the process to ascertain if the adjoint process is accurately predicting the actual performance and converging towards an optimal solution. The experimental validation will be accomplished by a combination of surface pressure measurement, drag measurement and measurement of the flow fields around the model. Beyond these technical goals is the high-level goal of transferring scientifically optimized race technology to the US Luge Association for use in Olympic competition.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.