Abstract
Evaluations of potential blade-strike on an axial-flow marine hydrokinetic (MHK) turbine were conducted using a method that integrates the following components into a computational fluid dynamics (CFD) model: (i) advanced eddy-resolving flow simulations, (ii) inflow turbulence based on field data, (iii) moving turbine blades in a transient flow, and (iv) Lagrangian particles to represent fish. The sensitivity of blade-strike probability to the following conditions was also evaluated: (i) turbulent environment, (ii) fish particle size and (iii) mean stream flow velocity. A limitation of the method is that fish are represented as particles that simply move with the fluid and can exhibit no behavioral response such as avoidance of the MHK turbine. This limitation causes a tendency for the model to overestimate strikes since it is likely that some fraction of an approaching population of fish would actively avoid the turbine.
The CFD-based blade strike simulations provide not only the frequency of collisions, but also insights into the causal relationships between the flow environment and resulting particle strikes on rotating blades. The results were compared against the outcomes of a conventional method that only considers the kinematic aspects of the fish passage event without any regard for the flow dynamics. Overall, the conventional method, while simple to apply, largely overestimates the probability of strike, and lacks the ability to produce potential fish and aquatic biota trajectories as they interact with the rotating turbine. In contrast the CFD-based Lagrangian method utilizes a set of experimental correlations of exposure-response of live fish colliding on moving blades, frequency of occurrence, intensity of the particle collisions to calculate the estimated survival rate of fish encountering the MHK turbine. Estimated survival rates were greater than 96%, which are comparable to or better than many conventional hydropower turbines. Although the proposed CFD framework is computationally more expensive, it provides the advantage of evaluating multiple mechanisms of stress and injury of hydrokinetic turbine devices on fish and relating those to specific design features of the MHK turbine.