Patent ID: 8784046

Claim:
A turbine for converting energy of a fluid to rotational energy, the turbine comprising: a blade; a structure body which has a space between the structure body and the leading end of the blade and rotates relatively with respect to the blade; a stepped part which is installed at the leading end of the blade and comprising a step surface to project toward the structure body; a seal fin which is installed at the structure body to extend toward the stepped part; a partition wall which faces the seal fin at the upstream side of the flow of the fluid in a direction parallel to the blade or a rotating shaft of the structure body; and a cavity which is formed between the leading end of the blade and the structure body and also between the partition wall and the seal fin; wherein when a small space formed between the seal fin and the stepped part is given as H, a distance between the partition wall and the seal fin which form the cavity is given as a cavity width W, and a distance between the seal fin and the end edge of the stepped part on the upstream side is given as L, at least one of the distances L satisfies the following formula (1). 0.7H≦L≦0.3W (1).