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PARTICLE-LADEN FLOW - ERCOFTAC SERIES Phần 7

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Tham khảo tài liệu 'particle-laden flow - ercoftac series phần 7', ngoại ngữ, anh ngữ phổ thông phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 250 M. Bourgoin P. Gervais A. Cartellier Y. Gagne C. Baudet Time s Fig. 4. Time-frequency representation. Two bubble signals are visible. D N Ls Lk T. Tt 58 3552 8.1 1.48 80 9584 5.7 1.22 93 7444 5.0 1.20 111 1358 4.2 1.02 Table 1. Experimental parameters at different distances D from the nozzle and the center of the measurement volume. D is measured in multiples of the nozzle diameter. N is the number of velocity segments. continuity exists between velocity segments they all correspond to different bubbles. Such a procedure leads to a large set of independent realizations of Lagrangian velocities. The j-th point time of the i-th segment realization will be denoted by Vj j . 4 Results 4.1 Data set As already discussed in order to resolve not only the small-scale dynamics but also the large-scale dynamics of the particles we need the measurement volume dimensions to be comparable to the integral scale of the flow. Therefore we carried the experiments in an air jet with a small nozzle 2.25 cm in diameter compared to the transducers diameter. As a consequence only moderate Reynolds number up to R 320 were achievable. Series of recordings were made at four distances D from the nozzle. Every measurement corresponds to the same Reynolds number as it is constant along the jet but to different integral length scales 9 8 10 . The measurement volume was centered on the jet axis to preserve cylindrical symmetry as much as possible. Table 1 lists the main parameters of the different measurements. The number of velocity segments exceeds 1000 for all measurements ensuring good statistical convergence. Measurement volume length is always several times larger than the Eulerian integral length scale Ls LE and the ratio of the average time-of-flight to the Lagrangian integral time scale Ts TL is everywhere above one. 3D acoustic Lagrangian velocimetry 251 4.2 Velocity probability density function The normalized velocity probability density functions PDF for the longitudinal velocity