“…With the increase of flow rate coefficients, the lost efficiency of the rotor decreases while the lost efficiency of the LKE increases. The similar phenomenon can be discovered in the experimental study carried out by Licheri et al 55 Figure 10.Lost efficiency of various components in the Wells turbine stage.…”
Section: Resultssupporting
confidence: 81%
“…With the increase of flow rate coefficients, the lost efficiency of the rotor decreases while the lost efficiency of the LKE increases. The similar phenomenon can be discovered in the experimental study carried out by Licheri et al55 Similarly, the loss audit analysis of rotors without guide vanes and with guide vanes was performed under the same conditions. The lost efficiency caused by the profile, endwall, tip gap leakage, and mixing losses under different flow coefficients is depicted in Figure11, where the color contours of the total entropy generation rate ( _ s t ¼ _ s vis þ _ s tur ) under three typical flow coefficients are also shown.…”
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.
“…With the increase of flow rate coefficients, the lost efficiency of the rotor decreases while the lost efficiency of the LKE increases. The similar phenomenon can be discovered in the experimental study carried out by Licheri et al 55 Figure 10.Lost efficiency of various components in the Wells turbine stage.…”
Section: Resultssupporting
confidence: 81%
“…With the increase of flow rate coefficients, the lost efficiency of the rotor decreases while the lost efficiency of the LKE increases. The similar phenomenon can be discovered in the experimental study carried out by Licheri et al55 Similarly, the loss audit analysis of rotors without guide vanes and with guide vanes was performed under the same conditions. The lost efficiency caused by the profile, endwall, tip gap leakage, and mixing losses under different flow coefficients is depicted in Figure11, where the color contours of the total entropy generation rate ( _ s t ¼ _ s vis þ _ s tur ) under three typical flow coefficients are also shown.…”
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.
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.
“…A sinusoidal piston motion is typically set to simulate a regular wave, as done in Refs. [9,12], while a triangular motion is set in this study to obtain a constant flow speed for a finite time interval. Both the amplitude and the period of the piston motion can be adjusted through the settings of the hydraulic unit.…”
Section: Experimental Facilitymentioning
confidence: 99%
“…Nevertheless, the flow field in a Wells rotor has not yet been completely explained, and only few detailed experimental analyses have been presented. More recently, Licheri et al [9] presented a local reconstruction of the flow field in a Wells turbine by means of an aerodynamic pressure probe, assuming the flow is two-dimensional, i.e., neglecting the radial velocity component. With a similar probe, Alves et al [10] conducted an analogous investigation for a biplane Wells turbine.…”
An experimental investigation of the local flow field in a Wells turbine has been conducted, in order to produce a detailed analysis of the aerodynamic characteristics of the rotor and support the search for optimized solutions. The measurements were conducted with a hot-wire anemometer (HWA) probe, reconstructing the local three-dimensional flow field both upstream and downstream of a small-scale Wells turbine. The multi-rotation technique has been applied to measure the three velocity components of the flow field for a fixed operating condition. The results of the investigation show the local flow structures along a blade pitch, highlighting the location and radial extension of the vortices which interact with the clean flow, thus degrading the turbine’s overall performance. Some peculiarities of this turbine have also been shown, and need to be considered in order to propose modified solutions to improve its performance.
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