![]() There is, however, an average configuration and that is what is reported in the experiments.įor all practical purposes the flow is two-dimensional, that is, it does not have any significant variation in the direction normal to the illustration in Fig. Strictly speaking, the flow conditions in the pool region are not steady because turbulent mixing is generated in the pool by the impinging fluid. At the bottom of the overflow a pool has formed between the overflow and the face of the step, while downstream, liquid is flowing to the right with a flat, steady surface. The overflow (sheet of liquid or nappe) leaving the top of the step has both an upper and lower free surface. Prototype Hydraulic Flow with Free Surfacesįigure 1a shows the flow problem after it has reached a steady-state condition. This flow has conceptual simplicity and good experimental data available for validation (see N. The example selected is of flow over a step. The goal of this discussion is to show why the VOF approach offers a natural way to capture free surfaces and their evolution with great efficiency.Ī good recommendation for the VOF method is to demonstrate its capabilities on a simple hydraulic flow problem, one that is far from trivial. This technique has many unique properties that make it especially applicable to flows having free surfaces. The technique is based on the Volume-of-Fluid (VOF) technique. In this note a computational modeling technique for fluid flows with arbitrary free surfaces is discussed. Changes in the solution region include not only changes in size and shape, but in some cases, may also include the coalescence and break up of regions (i.e., the loss and gain of free surfaces). A free boundary poses the difficulty that on the one hand the solution region changes when its surface moves, and on the other hand, the motion of the surface is in turn determined by the solution. The difficulty is a classical mathematical one often referred to as the free-boundary problem. Not many programs are capable of including free surfaces in their simulations. Many computer programs can solve the partial differential equations describing the dynamics of fluids. To be useful, simulations should be much faster and less expensive than using physical models. A capability to computationally model these types of flows is attractive if such computations can be done accurately and with reasonable computational resources. Examples in hydraulics are flows over spillways, in rivers, around bridge pilings, flood overflows, flows in sluices, locks, and a host of other structures. Fluid flow problems often involve free surfaces in complex geometry and in many cases are highly transient. ![]()
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