Can I Use Transition SST turbulence model for turbine or rotor in Ansys Fluent ?

 Yes, you can likely use the Transition SST model for your Darrieus turbine simulation in ANSYS FLUENT given the y+ wall value of approximately 1. Here's why:

 * Transition SST Applicability: The limitations mentioned in the FLUENT manual you quoted are mostly relevant if you're dealing with:

   * Free shear flows (no walls)

   * Moving walls relative to the simulation domain

   * Fully developed pipe/channel flows (no freestream)

   * Buoyancy-driven flows or multiphase flows (e.g., water-air mixtures)

Since your Darrieus turbine is a wall-bounded flow with a well-defined freestream velocity (the water flow in the pipe), the Transition SST model is generally applicable.

 * y+ Wall Value: A y+ value around 1 indicates that your mesh is sufficiently refined near the wall to capture the boundary layer effects, which is crucial for transition modeling.

Therefore, using the Transition SST model for your Darrieus turbine simulation seems appropriate based on the information provided.

Cautions and Recommendations:

 * While the Transition SST model is a good choice, it's always advisable to consult the ANSYS FLUENT documentation for best practices and potential limitations specific to your turbine geometry and flow conditions.

 * Consider running simulations with both the Transition SST model and a simpler model (e.g., Spalart-Allmaras) to compare the results and assess the impact of transition modeling on your specific case.