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Influence of wall roughness on boundary layer transition position of the sonic nozzles

2019; Elsevier BV; Volume: 139; Linguagem: Inglês

10.1016/j.measurement.2019.01.091

1873-412X

Chao Wang, Peijuan Cao, Chunhui Li, Hongbing Ding, Lishui Cui,

Advanced Sensor Technologies Research

The discharge coefficient of sonic nozzle is mainly dependent on the viscous boundary layer which is affected by the Reynolds number, wall roughness and turbulence intensity. Six sonic nozzles with various throat diameter of (1.921–9.086) mm and the average roughness of 0.6 μm in NIM were designed and calibrated to experimentally analyze the influences of wall roughness on the discharge coefficient and boundary layer transition by two pVTt gas flow standard facilities. Furthermore, a series of numerical simulations through the transition SST model for the axisymmetric nozzles were established to research the discharge coefficients of the sonic nozzles with the throat diameter of 3.808 mm, 5.350 mm and 7.453 mm when the Reynolds numbers ranges from 2.5 × 104 to 4.4 × 107 and the relative equivalent sand roughness Ks/d from 1.3 × 10−5 to 1.3 × 10−3. The calculating results of the simulation model were validated by the ISO 9300 empirical equation and the experimental data of NIM, PTB and UK. Finally, the relationships between the displacement thickness of boundary layer, namely the discharge coefficient and the relative roughness of the wall were obtained in detail. The starting positions of boundary layer transition with different Reynolds number and relative roughness were also analyzed.