2-d flow over buildings
 

hello,
I have a project for school that i have to use fluent for. I am trying to find the best place to put a chimney on a building. the situation is, there are two 40m tall buildings 50m apart. 15 meters from the left building there is a 20 meter tall building. it is 15 m wide so that there is 20 meters between the middle building and the building to the left. a chimney somewhere on the top emits water vapor.

my goal is to minimize vapor concentration against the two tall buildings. i am trying to run this simulation in fluent. i have to run a full scale model and a small scall model(140meters=.03meters). i am able to get the small scale model to converge perfectly, however, the full scale model just keeps saying turbulant viscosity limited to 10e5 in xxx cells. the number of cells varies but the residuals just follow a sinusoidal wave form and never go down enough to converge.

my question is, how can I fix this. i have tried many different mesh combinations is gambit and dont have any wornings about the mesh.
thanks,
chris