Experiment on flow dynamics and cavitation structure in an axisymmetric venturi tube based on x-t diagrams and proper orthogonal decomposition

Abstract

The shedding mechanisms of unsteady cavitation flow in venturi tubes are key problems in the study of cavitation flow, and cavitation dynamics in different venturi tubes differs owing to the difference of operating conditions and geometric parameters, so different results still exist among academics. In this paper, the flow dynamics and cavitation structure induced by shedding of sheet/cloud cavitation in an axisymmetric venturi tube under different flow conditions were investigated experimentally by combining x-t diagrams and the proper orthogonal decomposition (POD) method. The cavitation dynamic shows that the combination of shock waves and re-entrant flow resulted in the shedding and collapse of the sheet/cloud cavitation in the tested venturi tube. Furthermore, the characteristic cavity length, shedding frequency are analyzed under different operating conditions. The relationships for predicting two typical cavity lengths Lt* and Lc* was proposed, and the transition cavitation number for Lt* and Lc* was constant (σc = 0.54). Finally, the feature information of the sheet/cloud cavitation flow and POD modes were extracted through proper orthogonal decomposition (POD) analysis, reducing the dimensionality of the complex process. The coherent structure of sheet cavitation, transition region and cloud cavitation and the characteristics of these structures with displacement versus period time were illustrated, and the irregular perturbation process of the microstructure induced by the periodic shedding of cavitation clouds was demonstrated. In summary, the shedding mechanisms of sheet/cloud cavitation and coherent cavitation structure in venturi are greatly clarified through this research, and the findings provide theoretical guidance for the application of venturi tubes from the perspective of cavitation prevention and utilization.