Abstract

An experimental study has been performed on a 1-m base diameter buoyant helium plume. Velocity fields were measured by particle image velocimetry (PIV). Helium concentration was determined by seeding the helium with 1.7-volume percent acetone vapor and measuring planar laser-induced fluorescence (PLIF) of the acetone. PIV and PLIF were performed simultaneously using a 200 Hz XeCl excimer laser and 35-mm motion picture cameras. The film images were digitized and post-processed to obtain velocity and concentration data for a region approximately 0.8 m high by 1 m wide centered on the plume centerline and extending from the surface of the plume inlet to include the pure helium core, near-field mixing zones, and surrounding air. The data cover 7 puff cycles of the plume. Instantaneous and time-averaged two-dimensional velocity fields were obtained for each of 900 time planes (129 time-planes per puff cycle) spaced 5 ms apart. Each vector represents a statistical estimate of the velocity in a 2.1 cm by 2.1 cm by 0.8 cm volume, which are overlapped by 50% in the vector plots. Time-averaged turbulent statistics (u′2¯, v′2¯, u′v′¯, and k) are also presented. The joint velocity and concentration data are used to calculate Favre-averaged statistics. Boundary conditions were carefully measured as the data are intended for development and validation of numerical simulations of buoyant turbulence using RANS and LES techniques. The results clearly show the dominant effect of puffing, measured at 1.55 cycles/sec for this plume, on the temporal and spatial development of the velocity field.

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