Study Of Hydrodynamic Characteristics And Gas-Liquid Two-phase Flow In Inner Flow Of Tandem Cascade

Complex gas-liquid two-phase flows in rotary impeller have always been focused by engineers and scholars. Bubble dynamics and cavitation mechanism are kept expected from today's view. Tandem cascade is originally applied in military affairs fields and blades with different lengths in pump and turbine can also be deemed as tandem cascade. Researches of hydrodynamics characteristics in tandem cascade and gas-liquid two-phase flow characteristics will serve for the base of cavitation behavior in relevant impeller.Theoretical analysis of cavitation phenomena around two-dimensional hydrofoils is conducted firstly and cavitation zone profile around NACA 4412 hydrofoil is iteratively solved. Centrifugal blade is cutted along its blade height and several flow sections are obtained. Cavitation characteristics near leading edge of each flow section are deduced with potential flow theory. To discover complex flow mechanism from fundamental flow parameters' distributions, closed circular water tunnel is adopted as a platform for experimental study of NACA 4412 tandem cascade and Hydrofoil 915 tandem cascade. Pressure distributions on foils' surfaces in tandem cascade are measured and pressure distributions under different Reynolds number (Re) and attack angles are acquired for the first time. In terms of interactions among bubbles, flow and boundary, gas-liquid flow patterns in tandem cascade are observed with high speed photography for the first time and provide significant information for analysis of inner flows of tandem cascade and definition of gas-liquid two-phase flow pattern as well. Evolution characteristics of local variation of bubbles and bubble agglomerates near the trailing edge are described for the first time and influence of flow on bubble characteristics is deduced. These results provide references for further study of inner flow of cascade and bubble dynamics, and drive further the interface behavior study in complex gas-liquid two-phase flows.Another research is devoted to cavitation in rotary impeller with tandem cascade and different foil chord lengths. Based on Reynolds averaged Navier-Stokes equation (RANS), three-dimensional cavitation model is built combined with interface tracking model and constitutive equation; With flow field of non-cavitating flow as the initial field, cavitation simulation is performed. Three-dimensional cavitation zone is depicted and position and profile of the cavitation are presented. These researches further enrich the flow mechanism in fluid machinery and knowledge about cavitation flow.