Numerical optimization techniques in flow design are often used to find optimal shape solutions, regarding, for instance, performance, flow behaviour, construction considerations and economical aspects. The present paper investigates the possibilities of using these techniques in the design process of a hydropower plant. This is realized by optimizing the shape of an existing sharp heel draft tube and validating the result with previously performed experiments. The actual shape optimization is carried out with the response surface methodology, by maximizing the average pressure recovery factor and minimizing the energy loss factor. The result from the optimization shows that it is possible to find an optimal solution on rather coarse grids. The location of the optimum is similar to the experiments, but the improvements are unexpectedly small. This surprising result indicates that the simulated flow field does not completely act as the real flow, which may be a result of the applied inlet boundary conditions, insufficient turbulence models and/or the steady flow assumption.