International Centre for Numerical Methods in Engineering
The shock wave appearance is one the most typical problems in the design of spillways. Their origin is any perturbation of a supercritical flow, i.e. any change from the uniform chute flow, such as chute curves, changes of chute slope, abrupt contractions and expansions, chute junctions, etc. They are characteristics of the supercritical flow, highly turbulent, that is produced in this type of structures. Currently, a preliminary design is proposed following experience-based criteria, which is later tested in laboratory before construction. Due to the high cost of laboratory testing of several solutions, this procedure often leads to the adoption of a design that probably is far from being optimum.
The ability of PFEM to simulate the movement of fluids, and specially to determine the location of the free surface, makes it especially suitable for the analysis of this phenomenon. The purpose of this research line is the validation of the method by the analysis of real cases, or using results obtained in laboratory tests.
PFEM has been applied to the analysis of shock waves in Itoiz Dam spillway shute. In this particular case, the spillway is a non-conventional one because of its converging walls. A physical model was developed during construction, to check the behavior of the chute. There was a great concern regarding the possible appearance of shock waves due to the mentioned geometry of the chute walls. Some modifications were made to the original design, so that, even though the shock waves could not be suppressed, the distribution of the flow in the entrance to the energy dissipator was regular for the design discharge.
The spillway was modeled using PFEM, and the behavior of the chute, both in its original and final designs was reproduced. Figure 1 shows videos of both cases.
Figure 1. Results given by PFEM with the original (left) and final (right) designs.