Challenges in assessing the grid sensitivity of hydro-turbine CFD simulations

Despite the great progress made over the last 20 years, making reliable predictions with CM is still a challenge. In fact the hydraulic machinery community rarely relies entirely on numerical simulations to provide final designs. The core of the problem lies with the estimation of the solution accuracy. Grid convergence studies are a useful way to check for grid independence and can provide some insight into the actual solution accuracy. However, conducting such studies for complex, detached flows involves many challenges among which: creating progressively refined grids and comparing with measurement results. This paper investigates this problem through the practical example of the BulbT experimental setup for which multiple CM runs were conducted.