ANSYS

** Turbulent viscosity limited to viscosity ratio of 1e+05 *** reason The possible *causes* for large turbulent viscosity ratio include: - Bad initial conditions for the turbulence quantities (k and e) - Improper turbulent boundary conditions - Skewed cells *** solution If the problem is not caused by *bad mesh*, then *the beginning of the phenomena* can usually be avoided by: -Turn off solving *turbulence equations* for the first 100-200 iterations -Turn on turbulence and continue iterations If the problem occurs *in the middle of the iteration process*, then use the following procedure: - Stop the iteration - Turn *off* all equations except the *turbulence equations* - Increase turbulence under relaxation factors (URFs) (k and e) to 1 and iterate for 20-50 iterations - *Turn back all equations* and reduce the turbulence URFs to 0.5-0.8 and then continue iterations - Repeat the above steps for several times For *faster convergence*, it might be useful to obtain an initial solution wit

‎ Table of Contents 1. Reverse flow    reversed_flow 1.1. reasons 1.2. solutions 1 Reverse flow    reversed_flow It is common to encounter the regions of reversed flow at the initial stages of the simulation – This is normal. However, if the “reversed flow” warnings do not disappear as the simulation progresses, then one needs to address the issue and move the outlet boundaries to a location where the inflow is no longer encountered. Normally, it has to do with the outlet boundary condition. if you were to use the "pressure outlet" boundary condition at the outlet, your outlet must be set far away from the object of interest. In Fluent, I normally use the " outflow" boundary condition at the outlet and it does not give me reverse flow. 1.1 reasons It is virtually impossible to prescribe correct values for varying turbulence characteristics, temperature and species concentrations in those cells

Calculate Cp history using Matlab input data : unscaled time history of moment/thrust example of input data, "moment.out" 4283 6.983 -0.1910873139538953 4284 6.984 -0.191019809738711 4285 6.985 -0.1909838904131738 4286 6.986 -0.190943968230172 4287 6.987 -0.1908886443401208 4288 6.988 -0.1908541205872921 1. To load input data: > load moment.out 2.  extract *time* and *unscaled moment* and assign it to a variable named "m" > m=moment(:, 3);    # assign the 3rd column data of "moment.out" to variable "m" > time = moment(:,2); 3. calculating power coefficient, Cp cp=coeff(m);  # "coeff " is a function to calculate the Cp of 3 rotor  based on input moment (one rotor ) 4. assign "time" and "cp" variables to a new variable "cp_his" > cp_his = [time cp]; 5. export/save the workspace variable, "cp_his", to a txt file > save -ascii cp_his.txt cp_his ## syntax: save