"LOCK-ON phenomenon" of circular cylinders with different diameter ratios
 

Hi
I am trying to do a simulation that research the wake flow behind Two side-by-side circular cylinders with different diameter ratios and at various net gaps.For this case,Re=2000,main cylinder(Diamter=2cm)/small cylinder(Diamter=1cm)=2, the net gap(the distance of net gap/the diameter of main cylinder)=0.75 and in the water tunnel.In experimental result that show the ratio of the characteristic frequencies of the narrow and the wide wakes equal 3.3.Therefore I define this phenomenon to "LOCK-ON"
Recently,I am using "Fluent" to simulate this phenomenon.Use same experimental conditions and assume 2-D turbulence model(I have try to use standard k-omega and 2-D LES model),but the simulated results alway appear to the ratio of the characteristic frequencies of the narrow and the wide wakes equal 2.
How can I improve some settings to match the experimental results?

Thank you in advance