Abstract <p>The paper analyzes results of straight-through gas-dynamic calculation of a small-size turbojet engine from the point of view of using different turbulence models and taking into account internal cavities. A satisfactory convergence was found when comparing the calculation data with the engine test results. It is shown that for determination of engine parameters and characteristics of units, the modeling without taking into account the internal cavities, which reduces the design problem amount, is sufficient. Taking into account the internal cavities at the stage of numerical simulation allows solving the additional design problems, namely, the definition of leakage from the flow part and the rotor axial force.</p>