while observing graph between flow coefficient and torque coefficient why torque coefficient suddenly drops?
At higher flow coefficient values, stall occurs due to flow separation and it is the reason for the rapid drop of torque.
With increased flow rates of liquid (or gas), the flow regime around the turbine blades changes. A stall occurs and the torque decreases.
The torque coefficient of a Wells turbine drops after a certain value of flow coefficient because of the effect of cavitation. Cavitation is the formation of bubbles in a liquid caused by a decrease in pressure. As the flow coefficient increases, the pressure in the turbine decreases and these bubbles form, reducing the efficiency of the turbine. When the flow coefficient reaches a certain level, the torque coefficient drops due to the decrease in efficiency.
To improve the performance of the Wells turbine with fixed guides, end plate designs and a rotating turbine head ring are proposed as a treatment for sharp blade tip. In this study, statistical analysis was performed using ANSYS-based fluid-based computational fluid dynamics (CFD) software and validated the corresponding test data. Flow fields are analyzed and non-dimensional CA, CT, and η coefficients are calculated under stabilization conditions. Numerical results show that the material in the Wells ring-type turbine occurs at a flow coefficient of ϕ = 0.36, and its maximum efficiency can reach 0.54, which is 16% higher than that of the unchanged turbine and higher by 9 % than- endplate-type turbine case. Additionally, quasi-steady analysis is used to calculate the optimal efficiency and output of the wave cycle under sinusoidal flow conditions. As a result, it has been found that the ring-type turbine is higher than other Wells turbines.
Article Numerical study on Wells turbine with penetrating blade tip ...
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