vortex shedding is strong on one side and weak on the other one
 

Hi,
I am a beginner of fluent user. Now I am observing the vortex shedding on the flow past bluff body with slit. I use the rng k-e model. The reynold number range is 2400 - 6e4, and turbulent intensity is 5%. The boundary condition is velocity inlet and outflow.
Now I'm facing with some problems. The vortex shedding is strong on one side and weak on the other one ( the contours of velocity magnitude is attached )
http://www.dumpt.com/img/files/7bqmt...ttax_thumb.jpg
So, I want to know how to solve it and what I do wrong. Any suggestion will be appreciated. Thanks in advance!!