Abstract
Cavitation is a common flow phenomena in most hydraulic turbines and has the potential to cause vibration, blade surface damage and performance loss. Despite the fact that crossflow turbines have been used in small-scale hydropower systems for a long time, cavitation has not been studied in these turbines. In this paper, we present the findings of a computational study on cavitation inception in crossflow turbines. Cavitation inception was assessed using three-dimensional (3D) Reynolds-Averaged Navier–Stokes (RANS) computations. A homogeneous, free-surface two-phase flow model was used. Pressure distributions on the blades were examined for different flow rates, heads and impeller speeds to assess cavitation inception. The results showed that cavitation occurs in the second stage of the turbine and was observed on the suction side near the inner edge of the blades. For the particular turbine studied, cavitation always occurred at shaft speeds greater than that, giving the maximum efficiency for each combination of flow rate and head. The implication is that the useful operating range of crossflow turbines is up to and including the maximum efficiency point.
Highlights
This paper reports the results of a computational study on cavitation in crossflow turbines using three-dimensional (3D) Reynolds Averaged Navier–Stokes (RANS) simulations
Before examining the main flow features to analyze the inception of cavitation, the predictive capability of the computational fluid dynamics (CFD) model for the turbine power output was assessed by comparing the CFD results against experimental results
It is assumed here that the two-phase steady Reynolds-Averaged Navier–Stokes (RANS) solutions are adequate to predict the onset of cavitation and, for brevity, we omit a detailed description of the URANS model
Summary
This paper reports the results of a computational study on cavitation in crossflow turbines using three-dimensional (3D) Reynolds Averaged Navier–Stokes (RANS) simulations. Crossflow turbines are the most commonly used turbines in low-to-medium head small-scale systems, usually in the range of 5–300 kW. These turbines have a number of desirable characteristics, such as simplicity of design and low cost to manufacture, sturdy construction and a relatively flat and good efficiency curve over a wide range of operating parameters. The flow passes radially through the impeller blades twice (Figure 1), the turbine is commonly known as crossflow turbine. The flow in a crossflow turbine is either a two-phase mixture of water and air or a three-phase mixture of water, water-vapor and air (if cavitation is present).
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