In the present study, a hybrid RANS/LES model and a correlation-based transition model were coupled for simulating flow involving massive flow separation and laminar-turbulent transition including crossflow direction. For this purpose, blending of IDDES model and the gamma- Re-theta t - CF+ transition model was accomplished in a tightly coupled manner. For validations, numerical simulations around a circular cylinder involving laminar flow separation without turbulent reattachment were conducted. Numerical simulations were also conducted for flows around an Aerospatiale A-airfoil at a larger Reynolds number accompanying turbulent flow reattachment. As an application of the present blended model for flows involving crossflow transition, calculations were performed for flows around a 6:1 prolate spheroid, and the results were compared with experiment and those without considering flow transition induced by the crossflow instability. Additional application was also made for flows around an ONERA M6 wing at a relatively high angle of attack, and the results were compared with those of the baseline models and experiment. It was founded that the results by the present blended model are in good agreements with experiment, and show improvements over other models by considering flow transition and unsteady flow feature simultaneously. It was concluded that the present blended model is useful for predicting flows involving massive flow separation and crossflow transition. (C) 2021 Elsevier Ltd. All rights reserved.