The actuator line model is used to study the vertically staggered wind turbine cluster composed of horizontal- and vertical-axis wind turbines (HAWTs and VAWTs) in a tandem layout. We consider three simple configurations, including VAWT upwind of HAWT (V + H), VAWT downwind of HAWT (H + V), and VAWT between the two HAWTs (H + V + H). A VAWT installed upwind of the HAWT can not only generate power by itself but can also enhance the power generation of the HAWT, and the total power increases by about 100 kW. When installed downstream the HAWT, the presence of the VAWT slightly reduces the power generation efficiency of the HAWT. However, the VAWT utilizes the increased wind speed between the HAWT and the ground and generates more power. The total power increases by about 60 kW. When installed between the two HAWTs, the beneficial effects of the VAWT on the downstream HAWT are not manifested. Nevertheless, the wind turbine cluster still generates 50 kW more power than that without the VAWT. Overall, even in the tandem layout where the wake effects are most pronounced, the collocation of VAWTs can still utilize the otherwise wasted wind resources, thus increasing the power generation density of wind farms.