In this study, an efficient numerical method for predicting the wake interference of multiple turbines is presented. The actuator line (AL) model instead of the geometry-resolved method is adopted to represent the rotor. The Large-eddy simulation (LES) is performed to predict wakes of multiple turbines operated in turbulent flows. An efficient immersed boundary (IB) method with moving least square reconstruction (MLS) is developed to model the nacelle and support structure of the tidal turbine. A simple wall function based on the MLS-IB method and boundary-layer equations is employed to compute the instantaneous wall shear stress. Laminar flow simulations of unsteady flows past a cylinder illustrate the accuracy of the wall function IB method. Finally, the proposed method is extended to study turbulent flow past tandem tidal rotors, in which the wake profile behind rotors is analyzed. The results are found to be in reasonable agreement with published data.