The Development of a Large-Scale Particle Tracking Velocimery System for Wake Analysis of Wind-Loaded Structures

Abstract

The current study examines the capabilities of large-scale particle tracking velocimet.ry (LS-PTV) in fully resolving the wake behind a wind-loaded structure. LS-PTV measurements within a 16m3 volume were acquired behind a 0.75m diameter sphere. The study uses a spherical obstruction as a base case to prove the feasibility of measuring wind- turbine wakes. The Reynolds number of the flow was approximately Re =1 x 105. The temporal longevity of paths increased at a rate of 0.0073D/Uo per sphere diameter, indicating that the seeding particles have the ability to withstand the shear forces present in the wake. Furthermore, the mean freest.ream-velocity deficit, profiles, the st.reamwise Reynolds stress profile, and the wake-deficit, decay obtained using the LS-PTV system agreed with studies performed by Amoura et. al. [1] and Eames et. al. [2], thereby demonstrating the system's ability to accurately quantify the mean flow. Finally, st.eady-flow, ramp-up and ramp-down events were identified within the data from the time trace of the freest.ream flow. The corresponding wake structures behind the sphere during the three events were characterized using the realtime spatial measurements achievable by the LS-PTV system. During steady-flow conditions, pat.hlines exhibited high mixing and high curvature within one diameter downstream of the sphere, whereas pat.hlines further downstream were comparatively straight. In contrast., the straightening of pathlines occurred further upstream during ramp-up and ramp-down events, indicating that, high freest.ream-velocity events such as gusts have an organizing effect, on the wake, which attenuates shedding structures.