This study examined blade tip loss to understand flow separation around H-Rotor Vertical-Axis Wind Turbines (VAWTs). Vortex development around the blade tip requires flow separation. Near the blade tip, separation creates concentrated vorticity and vortices. Blade tip vortices affect Vertical Axis Wind Turbine (VAWT) efficiency. Understanding flow separation and vortex dynamics improves VAWT performance. This study uses 3D CFD using the Improved Delayed Detached Eddy Simulation (IDDES) turbulence model. Simulation accuracy can be studied using several test cases with different grid densities and time step durations. Comparisons include instantaneous, overall blade torque coefficient, and span-wise torque coefficient. The mid-span of the blade has the maximum torque coefficient, which drops towards the tip, reducing performance owing to tip loss. This shows that IDDES can capture blade tip vortices' creation and behaviour. Comparing IDDES simulation results with experimental data shows that it can simulate sophisticated H-Rotor VAWT vortex dynamics. Blade tip vortices affected H-Rotor VAWT torque in this investigation. The IDDES turbulence model, mesh, and time step selection demonstrate the importance of correct simulation in VAWT performance optimisation. Energy efficiency is improved by more precisely designing and operating complicated wind energy systems.