Resumo

CRUZ-MAYA, J. A.; SANCHEZ-SILVA, F.; QUINTO-DIEZ, P.  e  TOLEDO-VELAZQUEZ, M.. J. appl. res. technol [online]. 2005, vol.3, n.2, pp.104-117. ISSN 2448-6736.

This paper identifies and determines the main parameters used to calculate the discharge coefficient of a toroidal Venturi nozzle according to the ISO Standard 9300, operating at the critical flow regime (sonic). This study was conducted to investigate the effects of the viscous stresses in the turbulent boundary layer, the wall thermal boundary condition, and the flow field curvature at the nucleus of the nozzle on the discharge coefficient by means of a theoretical and numerical approach. Characterization of the discharge coefficient in the Venturi sonic nozzle was performed considering the viscous and multidimensional effects of the fluid flow as uncoupled phenomenon. As a result, each non-ideal mechanism can be analyzed independently from the influence of the other mechanism. We present a numerical procedure to characterize the discharge coefficient in the inviscid region of the flow, by using the numerical simulation of the inviscid main flow by means of the commercial CFD code. In the region of the viscous stresses, the characterization of this coefficient is based on the analytical theory of the turbulent boundary layer. This characterization allowed obtaining a correlation of the discharge coefficient that was validated by direct comparison between the experimental correlations of the discharge coefficient in turbulent boundary layer proposed by ISO-9300 and the Korea Research Institute of Standards and Science (KRISS). This validation was carried out for throat Reynolds numbers from 1.4 to 2.6x10⁶. The agreement of the theoretical and measured discharge coefficients by these correlations was better than 0.2%.

Palavras-chave : Critical Nozzle; Discharge Coefficient; Critical Flow.

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