Abstract:In this study, unsteady numerical simulations of centrifugal compressors with and without volute were carried out. The unsteady two-phase region evolution in the centrifugal compressor is obtained. Large coherent perturbations were revealed by the decomposition of the transient flow data using the dynamic mode decomposition (DMD) approach. The results imply that because of the low static pressure strip LP1, the two-phase region presents a triangular distribution at the blade leading edge (LE) of the pressure s… Show more
“…Structured multiblock grids were used to discretize the computational domain using the commercial code IGG. 44 To ensure sufficient solution accuracy in the boundary-layer region, the y + values of the blade surfaces and endwalls were below 1, so that the viscous sublayer could be resolved with no near-wall modeling.Figure 3.Scheme of the computational domain and grids on the wall.…”
Section: Physical Model and Numerical Configurationsmentioning
To provide deep dives about aerodynamic loss mechanisms in Wells turbines for wave energy conversion, a loss audit analysis was performed by numerical experiments in a monoplane Wells turbine with guide vanes. The interactions between the tip-leakage and leading-edge vortices during the stall process were captured by an improved vortex identification method, which revealed the relationship between vortex interactions and stall mechanisms by identifying coherent structures and tracking the vortex core trajectory. Finally, the influence of vortex interactions on exergy transfer was quantified. The results indicate that the lost kinetic energy and mixing losses dominate the loss generation in the Wells turbine stage under stall conditions. Under the beneficial effect of tip leakage flow, leading-edge separation first begins at the equilibrium region between the tip-leakage and leading-edge vortices. As the leading-edge vortices expand toward the blade tip, the intensified leading-edge vortex interacts with the casing suction-side corner vortex and accelerates the dissipation of the tip-leakage vortices. Consequently, the contributions of viscous irreversibilities outweigh those of shaft work, being the dominant factor in the decrease in flow exergy, leading to a decrease in exergy utilization by 38.46% from the pre-stall condition to the stall condition.
“…Structured multiblock grids were used to discretize the computational domain using the commercial code IGG. 44 To ensure sufficient solution accuracy in the boundary-layer region, the y + values of the blade surfaces and endwalls were below 1, so that the viscous sublayer could be resolved with no near-wall modeling.Figure 3.Scheme of the computational domain and grids on the wall.…”
Section: Physical Model and Numerical Configurationsmentioning
To provide deep dives about aerodynamic loss mechanisms in Wells turbines for wave energy conversion, a loss audit analysis was performed by numerical experiments in a monoplane Wells turbine with guide vanes. The interactions between the tip-leakage and leading-edge vortices during the stall process were captured by an improved vortex identification method, which revealed the relationship between vortex interactions and stall mechanisms by identifying coherent structures and tracking the vortex core trajectory. Finally, the influence of vortex interactions on exergy transfer was quantified. The results indicate that the lost kinetic energy and mixing losses dominate the loss generation in the Wells turbine stage under stall conditions. Under the beneficial effect of tip leakage flow, leading-edge separation first begins at the equilibrium region between the tip-leakage and leading-edge vortices. As the leading-edge vortices expand toward the blade tip, the intensified leading-edge vortex interacts with the casing suction-side corner vortex and accelerates the dissipation of the tip-leakage vortices. Consequently, the contributions of viscous irreversibilities outweigh those of shaft work, being the dominant factor in the decrease in flow exergy, leading to a decrease in exergy utilization by 38.46% from the pre-stall condition to the stall condition.
“…This configuration of the computation domain can ensure the full development of the inlet and outlet flows. 34 Hexahedral structured mesh generated by IGG v8.9 software 35 was employed to discretize the computation domain. As depicted in Figure 4(b), the grids near the endwall and blade wall were refined to meet the requirement that y + is close to 1 for the two-equation turbulent closure model.…”
Section: Numerical Configuration and Validationmentioning
Monitoring of aerodynamic parameters of the blade helps to enhance the operating capabilities of the Wells turbine. In this study, a few discrete pressure points were used to estimate the pressure patterns by fitting the exact potential-flow solution for flow over a parabola. The sectional aerodynamics was assessed by the leading-edge flow sensing (LEFS) algorithm. A characteristic parameter was employed to deduce leading-edge flow status. Moreover, the influence of rotor speeds and tip gaps on the vortex boundary was discussed in terms of the Lagrangian frame. For the rotor speed larger than 1000 rpm at the incipient stall point, there is no boundary layer separation at the suction side of the blade tip leading edge. At the same rotor speed, a large tip gap reduces the axial shear of the suction flows and the axial stretching of the tip leakage vortex, which helps to enhance the interaction time and strength of the leakage vortex and the suction flows. For the Wells turbine with attached flows, the LEFS algorithm can accurately evaluate the pressure distribution and suction parameters near the leading edge. The LEFS-derived dimensionless parameter can act as an equivalent angle of attack under different tip gaps, providing the possibility for stall warning of Wells turbines.
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