Experimental investigation on the vortex-induced vibration of a three-riser group coupling interference effect

•An experiment on VIV coupling interference of a three-riser group at varying angles.•Frequency interference ratio, displacement interference efficiency are introduced.•Shadowing effect and mode transition have great impacts on 0°- and 45°-riser groups.•At 60°, the St numbers peak, and the traveling wave characteristic maximize.•Interference effect on the riser group at low velocities should not negligible.