Under the CLEANSKY 2 framework SONACA and Von Karman Institute of Fluid Dynamics, establish the Research and Innovation Action MOTHIF (MOdel Testing of HIgh lIFt model) consortium with Piaggio Aerospace as Topic Leader. Funded by the European Commission under the Horizon 2020 program, it was in charge to validate with wind tunnel testing a selected high lift device system for Small Air Transport aircraft (SAT). The wind tunnel tests have been performed in the open-jet test section of the Von Karman Institute of Fluid Dynamics low-speed wind tunnel L1-A. The wing model, representing a blown flap airfoil in which an air jet from the main trailing edge skims the flap upper side, was very large due to the accommodation of the pneumatic feeding into the trailing edge main airfoil. The ratio between the test chamber diameter and the test model large dimension necessarily led to blockage effect. The Digital Twin approach based on CFD (Computational Fluid Dynamic) computation helped the identification of the aerodynamic interference between wind tunnel and the airfoil model and significantly contributed to the test success.