Hello!

I am about to start a theoretical study of flow around a circular bridge pier with a circular collar. The pier is placed on an erodible sandy bed and there is, obviously, bed scour. The purpose of the collar is to achieve a reduction in the maximum depth of scour. I would like to use a k-epsilon model but in view of the fact that the flow has swirls and vortices, the computational results may not be very good. Any suggestions?

Regards,

Amartya

(1). It depends on the goal of this theoretical study. (2). From practical point of view, a 3-D laminar flow calculation should provide some useful flow field information about the problem and the design solution. (3). A two-equation k-epsison turbulence model should be an improvement, if you know how to handle the boundary condition for separated flow cases. (4). The study of turbulence modeling with strong swirl effect could be an interesting subject of research. (5). Most 3-D CFD results are not very good because of inadequate mesh resolution. So, if you plan to get good results, make sure that you have a computer with large enough memory .(or you may have to use parallel processing on several computers).

Most of the commercial software does not include swirl terms. If I were in your situation then I would consider of searching for the universities that are working on swirl, vorticity dynamics etc. I think that is agood start.

Hi There,

This sounds like a very interesting problem involving a lot of complicated processes.

With a fully 3D model you might expect the collar to induce in the flow streamwise vortices (which themselves might be responsible for turbulence) downstream. So that looks pretty complex and attracting. You will need to resolve the streamwise vortices and the turbulence. Since the transition to turbulence here is sub-critical (non-linear), there is a regime in which the flow is laminar and another one in which it transits (locally) to turbulence (for example if the stream if slow the flow is laminar, and when the stream is fast the flow is turbulent downstream).

You could try as a first stage, just a pier without a collar and assuming a shallow water approximation for the flow, so that as a first step you look at a simple 2D problem. This might be able to represent the surface flow pretty well.

Good luck, and keep us inform of your results. Patrick.