Computational Method for Designing a Nozzle Shape to Improve the Performance of Pico-Hydro Crossflow Turbines

Abstract

The nozzle in a crossflow turbine is important because it accelerates the flow of the inlet and directs it to the runner at an angle relative to entrance angle (β1), which is used to obtain the maximum efficiency value. The β1 value must match the angle of the runner's outer blade considering the transfer of water from stationary to the rotating coordinates. To obtain the desired β1 value, the design of the nozzle is essential. In this study, 6-DoF simulations were conducted to find the best nozzle geometry. The incoming flow angles (λ) of the nozzle ranged from 50° to 90°. A study without a proper nozzle design was also conducted to compare the results. The results showed that a nozzle geometry of λ = 50° yielded the highest efficiency (60.6%). This study shows that the design of the nozzle in a crossflow turbine significantly affects its performance.

Performance Comparison of Crossflow Turbine Configuration Upper Blade Convex and Curvature by Computational Method

“…In Figure 6-a, we can see that the curved blade has a better performance (76.94%) than the convex blade (76.84%). Compared to a previous study [10], the CFT upper blade geometry (convex and curvature) changes went further to improve its performance, from a 61% [10] improvement to 76.84% (convex blade) or 76.94% (curved blade). Yet, the relationship of η with n is similar to in the previous study [18,23], which verifies the simulation results.…”

“…Figure 2 presents the CFT's design; the lower blade design follows [22], and the nozzle design follows [18] enhanced by [10]. We employed analytical calculations using the study concept from [22] (validated by Adhikari and Wood [23]), with an optimum angle of attack (α1) of 22°, blade angle at the inlet (β1) of 40°, and blade angle at the outlet (β2) of 90°.…”

“…There are three options for operating a CFT at a low head: design an inlet similar to a volute for parallel velocity vectors so that the momentum of the water to be transferred to each blade is proportional; increase the lift force, for instance, through the design of the CFT's upper blade; or optimize the ratio between the active and inactive blades. When we consider the first option, the nozzle geometry (incoming jet angle) is important to increase the discharge and the vector of the jet velocity [10]. An incoming jet angle (λ) of 50° was suggested in one study to indicate more profitable hydraulic behaviour than 60° to 90° [10].…”

“…When we consider the first option, the nozzle geometry (incoming jet angle) is important to increase the discharge and the vector of the jet velocity [10]. An incoming jet angle (λ) of 50° was suggested in one study to indicate more profitable hydraulic behaviour than 60° to 90° [10]. Then, other studies recommended an λ of 60° after exploring a study range from 60° to 80° [11,12].…”

“…Then, other studies recommended an λ of 60° after exploring a study range from 60° to 80° [11,12]. All three studies cited [10][11][12] showed that the λ significantly affects the CFT performance and indicated the possibility that lower λ angles produce a better performance. In contrast, Anand et al [13] hypothesized that a 90° λ should be used for the optimum efficiency; however, the authors failed to comprehensively explain the performance of each case in their report (which included a variation λ) [13].…”