A key the connection of computational fluid dynamics (CFD) and renewable energy engineering is modern water turbine design. Although hydropower systems can reach amazing efficiency rates above 90%, increasing turbine performance through modern CFD simulation—especially with sliding mesh techniques—has become crucial in extending these limits. From micro-hydropower plants to massive facilities, detailed fluid-structure interactions within water turbines necessitate advanced analysis techniques to capture events including cavitation, vortex shedding, and pressure changes. Particularly considering the complex interaction between rotating and stationary components, these dynamic systems provide special difficulties in numerical modeling. Sliding mesh CFD simulation has become a very effective method for examining rotor-stator interactions, wake dynamics, and turbulent flow patterns, therefore allowing engineers to predict and improve turbine performance throughout a range of operational settings. Note that, this is SESSION 13 of ANSYS Fluent Course For BEGINNERS.

Figure 1: Crossflow Water Turbine CFD Simulation Using Sliding Mesh – ANSYS Fluent Tutorial

Simulation process

The simulation has been carefully set up using the sliding mesh (Mesh Motion) method. This involves dividing the area being studied into two parts: one part includes the rotating crossflow turbine blades, and the other part represents the still fluid around them. The Volume of Fluid (VOF) multiphase module has been used to effectively show how water and air interact, and a Transient analysis method has been used to model how the fluid system changes over time. The computational domain has been discretized using 49,879 quadrilateral cells, with particular attention being paid to the implementation of a boundary layer mesh configuration around the crossflow turbine blades to ensure improved resolution of critical flow characteristics.

Figure 2: Mesh with boundary layer on crossflow water turbine blades

Post-processing

With important velocity gradients near the blade paths, the streamline visualization and velocity contours expose difficult flow patterns around the turbine at t. Especially in the areas between blade passages where flow acceleration results from area reduction, the maximum velocity magnitude reaches about 3.22 m/s. indicative of velocity deficits and recirculation zones, the wake region downstream of the turbine shows unique vertical structures and flow separation patterns. Understanding the performance aspects of the crossflow turbine and the momentum exchange between the fluid and the rotating components depends on these flow parameters.

Figure 3: Velocity & streamlines distribution in Crossflow Water Turbine CFD Simulation Using Sliding Mesh

With evident interface deformation close to the turbine area, the Volume of Fraction (VOF) contour shows the different interface between the water and air phases. Complex secondary flows and turbulent mixing in the wake area result from areas of high-velocity fluid interaction with the blade surfaces indicated by the stationary frame velocity distribution. These multiphase interactions together with the spinning turbine shape produce notable interfacial instabilities and wave generation patterns that affect the general system hydrodynamics. Analysis of the operational efficiency of the turbine and its effects on the surrounding flow field depends especially on these events.

Figure 4: Volume fraction of air  in Crossflow Water Turbine CFD Simulation Using Sliding Mesh