External aerodynamic optimization of ground vehicles using the adjoint method
Typ
Examensarbete för masterexamen
Program
Publicerad
2021
Författare
Lange, Gustau Lundegaard
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
The adjoint optimisation method within the field of ground vehicle aerodynamics has been a topic of continuous discussion in regards to advancing vehicle performance and decreasing development time. Conversely, the adjoint method has been limited by assumptions, stability issues, and increased computational cost. This thesis aimed to objectively demonstrate the capabilities of the newly implemented adjoint solver in OpenFOAM v2006, and its applicability to current development methods of Koenigsegg Automotive AB. First, a primal solver setup was validated on the DrivAer model by comparison of well-studied experimental force coefficients, pressure coefficients, as well as velocity and wall shear stress fields. The adjoint solver was investigated further on the DrivAer model by a parametric study of various mesh and solver settings, along with their impact on the sensitivity maps, which inform the engineer of potential areas of optimisation. Significant importance of the mesh quality and rotational boundary conditions have been observed on the sensitivity maps. Stability issues were encountered but mitigated, while retaining certain accuracy. Use was extended to a development CAD model of the Koenigsegg Regera to investigate stability and capability of the simulation at Re>20E6, and when adding porous zones. Steady optimisation with the Spalart-Allmaras turbulence model was validated by running three independent simulations with different two-equation turbulence models and notable drag minimisation was achieved within four cycles for the DrivAer model. Unfortunately, the steady optimisation proved to be unstable when morphing the finer mesh of the Regera and in areas of separated and highly rotational flow. Implementation of the adjoint method in external aerodynamic development of ground vehicles at Koenigsegg is possible under supervision of engineers. However, the adjoint method remains partially hindered by choice of adjoint turbulence modelling, mesh sensitivity, modelling accuracy, and compromised in regions of separated and highly rotational flow.
Beskrivning
Ämne/nyckelord
Adjoint method , aerodynamics , ground vehicles , DrivAer , Koenigsegg , optimisation , sensitivity maps