Water tank experiments have been carried out to investigate the influence of a double mountain obstacle on rotors beneath trapped lee waves. To trigger trapped lee waves a density jump was created by using saline. By towing the obstacle along the bottom of the tank a constant initial velocity was imitated. For the visualization of the flow, particles of different density have been added that float at different heights. Moveable and fixed cameras were used to take pictures of the flow during the experiment. Using Particle Image Velocimetry (PIV) instantaneous velocity fields were obtained. Analysis of the data showed a dependency of rotors on non-dimensional mountain distance, mountain height ratios and type of interference. A comparison of composite pictures showed that coinciding downslopes of the wave and the second mountain are needed to obtain rotors. This was observed for the ridge separation distance being a bit shorter than a multiple of the single mountain lee wave wavelength. In these cases, all experiments that were investigated featured constructive interference and mountain height ratios of H2/H1 = 1. Rotors as well occurred when the ridge separation distance was a bit longer than a multiple of the single mountain lee wave wavelength. The strongest rotors in this case were obtained for constructive interference and mountain height ratios of H2/H1 = 2/3 which leads to a coincidence of the downslopes as well.