Y+ Calculation for flow through variable area duct
 

I could find materials related to y+ calculation for flow through duct which is of constant cross-sectional area. I want to know if there is a different method for finding the first cell height for a converging diverging nozzle. What reference length should be considered in such a case? Since the y+ value varies throughout the length of the nozzle, what value of y+ should be considered for calculation?
Please direct me to any threads if available already.
Thanks in advance!!

As a first, rough, method, you could use as input velocity the average one in the given section, using the continuity to determine it for each section (given it for, say, the inlet section). But there is actually not much more you can do, besides trial and error