In the present work, a low-fidelity three-dimensional approach has been developed for the prediction of the flow around shrouded rotors. This method is to be used in the initial steps of design, for a wide exploration of the design space, including disruptive geometries, at minimal cost. The present approach is based on the vortex lattice method. First, the formulation on rotating geometries is validated by comparison with experiments. The Prandtl-Glauert correction is introduced to account for mild compressibility effects. A discretized approach is proposed to model the casing and simulate the tip-leakage flow. The results are discussed for different tip-gap sizes. A periodic boundary condition is also proposed and validated. This condition, together with programming techniques, decreases the computational and memory costs of the method. On average, a computation takes approximately one second to execute in real time. Finally, the method is applied to a shrouded fan configuration and the influence of the tip-gap size is analyzed.