to inflate and deflate the elements 9 with air fig7 shows a fourth embodiment of the strake 2 the strake 2 comprises a triangular shape in a crosscut perpendicular to the longitudinal axis of the strake 2 the triangular shape of the strake 2 is achieved by combining cylindrical elements 9 c whereby the elements 9 c all comprise the same diameter to achieve a triangular shape three six or ten elements 9 c can be combined the elements 9 c are arranged in parallel to each other each of the elements 9 c comprises a sealable opening or a valve to inflate or to deflate the strake element thus the strake 2 comprises a triangular shape when the elements 9 c are inflated with a fluid the strake 2 can be deflated by opening the valve 15 to reduce the overall volume of the strake and to facilitate the storage of the strakes 2 the elements 9 c can be tubes of a plastic of rubber material for example thus the elements 9 c of the strake 2 are elastically flexible and can be rolled up on a wheel when the elements 9 c are deflated fig8 shows an arrangement to install the strakes on the outer wall of a wind turbine tower the arrangement comprises a mounting bracket 10 to mount the arrangement to the upper end of a wind turbine tower the upper end of the wind turbine tower in fig8 comprises a flange and the mounting bracket 10 is screwed to the holes in the flange of the wind turbine.