Initial conditions k and epsilon

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 April 9, 2016, 05:59 Initial conditions k and epsilon #1 New Member   Join Date: Oct 2015 Location: Oviedo, Asturias, Espaņa Posts: 17 Rep Power: 10 Hello all! I have been simulating the effects of the Atmospheric Boundary Layer (ABL) on a 3D high rise building with different Steady RANS turbulence models such as Standard kE, kOmega, kOmegaSST, realizable kE and RNG kE. I have taken the Cd on the building and the Cp at 2/3H as 2 of my reference values in order to establish a comparation between my simulations with those 5 models and previous similar studies. However, the Cp obtained in all of my calculations is quite larger than those obtained by the mentioned previous studies. Apart from the mesh, which i have already checked and it is not the problem at all, i think that maybe I have used wrong values as the initial conditions of k, omega or epsilon. My current values are: turbulent kE: 0.7 turbulent epsilon: 2.0 turbulent omega: 3.0 My inlet U profile is based on a logaritmic law, and reachs 14.5 m/s at the roof. Uy and Uz are zero in the initial conditions. By the way, I have read about a estimation based on the turbulent intensity. However, since I only use steady RANS models, I cannot estimate that intensity. Are my initial values good? How should I change them if not? Do you know any way of estimate them? Thank you all Any advise will be absolutely helpful.

 April 15, 2016, 02:04 #2 Senior Member   david Join Date: Oct 2012 Posts: 142 Rep Power: 13 if you are using the log-law for velocity, then k and epsilon have to follow the formulations of the loglaw. Note that the loglaw is the balance between production of k and epsilon. in other words, uv du/dy = epsilon . Epsilon here has a y dependence which means you cannot assign it a fixed value. epsilon in the log-law ( local equilibrium) equals (friction velocity)^3/(kappa*y). and k in the log law is (friction-velocity )^2/(sqrt C_mu). Also, i would not use the standard k-epsilon for these type of flows because of the so-called stagnation point anomaly ( spurious production of k at stagnation region)

 Tags initial conditions, k epsilon, omega, rans, steady