“…Moreover, the endwall loss starts to increase from the stall point ( φ 2 = 0.175), which may be caused by enhanced secondary flow. 39 Figure 11.Loss audit and entropy generation rate of (a) the rotor with guide vanes and (b) without guide vanes under typical conditions.…”
Section: Resultsmentioning
confidence: 99%
“…Moreover, the endwall loss starts to increase from the stall point (φ 2 = 0.175), which may be caused by enhanced secondary flow. 39 Consequently, the loss generation and underlying flow patterns in the Wells turbine are significantly affected by the TLV, especially under the stall condition with the interaction of the LEV. Therefore, in the following sections, a detailed analysis is performed based on the rotor with guide vanes, providing a deep insight into the interaction of the TLV and LEV and the effect on the exergy transfer.…”
Section: Loss Audit Analysis Based On Numerical Testsmentioning
confidence: 99%
“…Although tremendous success has been achieved in the loss evaluation of Wells turbines by twodimensional 33,34 and three-dimensional numerical calculation of entropy generation [35][36][37] or total pressure coefficient, 38 detailed knowledge of the loss sources in Wells turbines remains limited. Recently, we performed a loss audit based on entropy generation, 39 where some of the loss quantifications, such as profile losses, are limited to two dimensions. In addition, the tip leakage and mixing losses caused by the interaction between the TLV and tip suction flow were not further distinguished.…”
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.
“…Moreover, the endwall loss starts to increase from the stall point ( φ 2 = 0.175), which may be caused by enhanced secondary flow. 39 Figure 11.Loss audit and entropy generation rate of (a) the rotor with guide vanes and (b) without guide vanes under typical conditions.…”
Section: Resultsmentioning
confidence: 99%
“…Moreover, the endwall loss starts to increase from the stall point (φ 2 = 0.175), which may be caused by enhanced secondary flow. 39 Consequently, the loss generation and underlying flow patterns in the Wells turbine are significantly affected by the TLV, especially under the stall condition with the interaction of the LEV. Therefore, in the following sections, a detailed analysis is performed based on the rotor with guide vanes, providing a deep insight into the interaction of the TLV and LEV and the effect on the exergy transfer.…”
Section: Loss Audit Analysis Based On Numerical Testsmentioning
confidence: 99%
“…Although tremendous success has been achieved in the loss evaluation of Wells turbines by twodimensional 33,34 and three-dimensional numerical calculation of entropy generation [35][36][37] or total pressure coefficient, 38 detailed knowledge of the loss sources in Wells turbines remains limited. Recently, we performed a loss audit based on entropy generation, 39 where some of the loss quantifications, such as profile losses, are limited to two dimensions. In addition, the tip leakage and mixing losses caused by the interaction between the TLV and tip suction flow were not further distinguished.…”
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.
“…The blade load decreases gradually along the blade chord. 50 With the increase in flow rates, the blade load near the leading edge increases significantly, and the threedimensional characteristics of the field are enhanced. For example, the load at the medium span is higher than that near the blade tip.…”
Section: Determination Of Sectional Aerodynamic Parametersmentioning
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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