Recently, the evaluation of the thermal environment of an engine compartment has become more difficult because of the increased employment and installation of turbochargers. This paper proposes a new prediction model of the momentum source for the turbine of a turbocharger, which is applicable to three-dimensional thermal fluid analyses of vehicle exhaust systems during the actual vehicle development phase. Taking the computational cost into account, the fluid force given by the turbine blades is imitated by adding an external source term to the Navier-Stokes equations corresponding to the optional domain without the computational grids of the actual blades. The mass flow rate through the turbine, blade angle, and number of blade revolutions are used as input data, and then the source is calculated to satisfy the law of the conservation of angular momentum.On the other hand, the energy loss of the fluid through the blades should become lower than the actual value because the friction loss on the blade surface is not considered. Therefore, corrective coefficient α is employed to adjust the total enthalpy to the actual value. Concretely, the value of α is determined by comparing the total enthalpy difference before and after the turbine calculated thermodynamically using the expansion ratio of the actual turbine and the value calculated from the computational fluid dynamics based on the proposed model. Altogether, the total enthalpy corresponding to the amount of friction loss is corrected by coefficient α, and the fluid force corresponding to the enthalpy is also corrected.