turbulence in turbulence
hi .. i am a novice inCFD.. i am modelling flow using ke model for turbulence. in the standard ke model equations( 2D), how can one integrate the rate of production of k or e terms over the control volume. i am integrating FVintegration over 2D space? 2) what can one take the relation for mixing length for flow over variable xarea with many internal obstructions? 3)we have two different ke model equations for low Re and high Re. how high or low should be this Re value for the use of respective equations?

Re: turbulence in turbulence
(1). The volume is always 3D, so, make the thickness equal to unit thickness. (2). If you are using mixing length, you need to know the distribution of it in the flow field. You can specify the mixing length distribution or you can use a model to calculate it. (that is your job) (3). As long as the universal loglaw portion of the velocity profile exists, you can always use the high Reynolds number model.(sublayer region excluded) (4). You can always use the low Reynolds number model for the whole flow field, any Reynolds number. So, you can not use the high Reynolds number model for the laminar and the transitional flow range. (it is the flow behavior associated with the Reynolds number, not the value of the Reynolds number itself.)

Re: turbulence in turbulence
Hi,
lowRe and highRe turbulence models could be a bit confusing a first. This Reynolds number is not related to the bulk Reynolds number, but rather a local Reynolds number. Generally a lowRe turbulence model needs to resolve the flowfield even in the viscous sublayer, while a highRe turbulence model is satisfied with placing the first interior calculation node in the logarithmic layer. The different regions are normally distinguished using a normalised wall distance, y^+=yu_{\tau}/\nu, where u_{\tau} is the friction velocity (u_{\tau}=\sqrt(\tau_w/\rho), \tau_w is the wall friction), y is the wall normal distance, and \nu being the kinematic viscosity. The viscous sublayer is below y^+=5, and using a lowRe turbulence model you need a number of nodes in this region, with the first below y^+=1. The logarithmic region starts at around y^+=30. Regards Jonas 
All times are GMT 4. The time now is 22:05. 