Tomographic Particle Tracking Velocimetry of Flow Around Buoyancy-Driven Transparent Solids

Refractive-index matching enables undistorted volumetric flow measurements close to transparent solids, but the same matching makes the moving body itself invisible. We present a tomographic particle tracking framework that locates a freely rising acrylic sphere directly from the flow it generates, combining three signatures: the tracer void left by the solid volume, the nearbody upward-velocity pattern set by no-slip, and the vortical wake structure. The recovered trajectory then drives pressure and force reconstruction. Experiments on three sphere diameters in a sodium iodide solution distinguish the straight two-ring wake of the smaller spheres from the asymmetric four-ring wake of the largest. A moving-boundary reconstruction that enforces no-slip at the detected surface further improves near-surface velocity and pressure consistency. The approach extends refractive-index-matched tomographic particle tracking from a flow-only measurement to a coupled body-wake diagnostic for transparent moving solids.