ABSTRACT A 3D hybrid mesh generation method was developed, which bases on an automatic 3D surface mesh generation method to form the body fitted mesh around the wall. The piecewise linear Morse theory was used to extract geometry features from 3D point clouds data, which includes feature points and feature lines of the geometric surfaces. The surface was then transformed from 3D physical space to 2D parametric space based on Least-Squares Conformal Mapping[1]. Combined with Cross-field [2][3] theory, the 2D geometry was partitioned in the 2D parametric space, and then maps back to the 3D physical space, thus achieving the automation of dividing the surface into multi-block structured meshes. Multi-block Structured body fitted mesh are then generated by extruding the surface meshes outward, followed by filling the far-field with unstructured meshes to achieve 3D meshes generation. The proposed algorithm is validated via spherical and ONERA-M6 wing models. Block partitioning results show smooth transitions at geometric joints, excellent orthogonality of each block, and high-quality structured meshes. These meshes are applied to simulate viscous flows over supersonic spheres and ONERA-M6 wings, post-processing results clearly capture shock waves, thus verifying mesh reliability. The proposed quadrilateral structural block generation algorithm enables efficient, rapid partitioning of bounded surface blocks with excellent orthogonality. Meanwhile, the body fitted meshes generated by this algorithm feature high automation and superior quality, providing an efficient mesh generation solution for subsequent numerical simulations. REFERENCES [1] Lévy B., Petitjean S., Ray N., et al., Least Squares Conformal Maps for Automatic Texture Atlas Generation, ACM Transactions on Graphics (TOG), 21(3)., 362-371., 2002. [2]Deng S. Q., Wang Y. B., Cross-Field Structured Adaptive Mesh Using Medial Axis Flow Feature Extraction, American Institute of Aeronautics and Astronautics Inc,62(1)., 247-262., 2024. [3] Fogg H.J., Armstrong C.G., Robinson T.T., Automatic generation of multiblock decompositions of surfaces. International Journal for Numerical Methods in Engineering, 101(13)., 965- 991., 2015.