Coherent Structures within the Laminar Separation Bubble on a NACA 0015 Hydrofoil

Abstract

Experiments were carried out in the cavitation tunnel CEIMM at INSEAN (Rome) on the suction side of a NACA 0015 hydrofoil model by means of Temperature Sensitive Paint (TSP). The investigations were conducted at angles of attack from 3° to 10° and at a chord Reynolds number of 180,000. A region of recirculating flow was identified confined between laminar separation and turbulent reattachment points; this region is commonly referred to as laminar separation bubble. The non-intrusive TSP approach enabled a description of the flow interaction with the body surface exactly at the wall avoiding appreciable flow perturbations or wall property modifications. In this work the focus is placed on the topology of the coherent structures that appear in the reverse flow inside the recirculating region at different angles of attack. A spatial frequency decomposition in low and high spatial frequency terms was used to separate the scales inside the separation bubble from the embedding environment.