Subject to present investigations is the numerical simulation of hypersonic flow in the flap region of the NASA/ESA/DLR X-38 reentry demonstrator, with respect to the heat loads downstream the reattachment line. With the DLR CFD code CEVCATS-N extensive calculations for flow conditions M=6 and Re=2.1 Mio to Re=8.8 Mio under 40° angle of attack and 20° flap deflection have been carried out with different mesh densities. Grid studies of the complete X-38 reentry configuration including wake and local refined grids in the flap region confirm good mesh convergence. Comparisons with wind tunnel testings at the Ludwieg-Tube wind tunnel in Göttingen show good agreement in the separation region for laminar and turbulent cases. Especially in the separation region in front of the hinge line satisfactory reliability of the algebraic turbulence model has been shown. Additional vortices are visible in the flowfield in laminar simulations with high grid resolution. Similar effects occur in the experimental cp distributions for laminar cases at Re=2.1 Mio and Re=3.1 Mio, as well as for turbulent cases at Re=4.2 Mio and Re=8.8 Mio, respectively. Surface temperature visualisations with liquid crystal technique for indication of the heat flux distribution and measurements by thin layer thermography complete the wind tunnel tests.