4 Replies Latest reply on Jun 13, 2014 3:48 AM by Mark Keown

    I-L relationship with k and e

    David Fredriksson

      Is there any documentation that describes how Flow Simulation relates I and L to k and epsilon?

        • Re: I-L relationship with k and e
          Jared Conway

          technical reference

          also the implementation is standard for flow simulation

           

          what type of problem are you running into that you need this info?

            • Re: I-L relationship with k and e
              David Fredriksson

              Hi Jared,

               

              This is not really my area of expertise, but it is my understanding is that k and epsilon are used to describe turbulent viscosity and are primary inputs to the "standard" model along with the Lauder and Sharma coefficients (which are embedded).  Flow Simulation also allows for the input in the form of turbulent intensity (I) and length scale (L).  This nomenclature is somewhat confusing with what some call a "zero-equation" mixing model, as opposed to the "two-equation" k-e modeling approach that Flow Simulation does.  But I am ok with that.    Now I have looked through the technical reference....and I can't seem to find the relationship between I/L and k/epsilon.  It would seem to me (this is where I really need the help), that if you specify I and L, it needs to be related to k and epsilon for use in the model - like in the discussion below.

               

              http://aerojet.engr.ucdavis.edu/fluenthelp/html/ug/node217.htm

               

              I hope this makes sense....

               

              Thanks,

               

              Dave F

            • Re: I-L relationship with k and e
              Mark Keown

              This may help - the "modified" and "two-equation" is the good stuff...

              It's turbulence capabilities have been validated against some classic industrial CFD cases. It utilizes a modified k-ε two-equation turbulence model designed to simulate accurately a wide range of turbulence scenarios in association with its pioneering immersed boundary Cartesian meshing techniques that allow accurate flow field resolution with low cell mesh densities. 

              The classical two-equation k-ε empirical model for simulating turbulence effects in fluid flow CFD simulation is widely used and considered reliable for most industrial CFD simulations and it requires the minimum amount of additional information to calculate the flow field. In FloEFD the k-ε model is used with a range of additional empirical enhancements added to cover a wide range of industrial turbulent flow scenarios (such as shear flows, rotational flows etc.). For instance, damping functions proposed by Lam and Bremhorst for better boundary layer profile fit when resolving boundary layers with computational meshes have been added. This is coupled to a unique Two-Scale Wall Function (2SWF) treatment. This two-scale approach allows FloEFD to overcome the traditional CFD code restriction of having to employ a very fine mesh density near the walls in the calculation domain.