The geometry was modeled using spaceclaim as 20cm diameter sphere inside 3m length*1m height*1m depth(0.5M symmetry was applied) fluid tunnel with the sphere center placed 1m away from the inlet

sphere radius was used as geometrical variable input 

Mesh was generated as a tetrahedral mesh with 100 mm mesh size, Body of influence around the sphere of 10 mm ,Face sizing on sphere walls of 1 mm and inflation around the sphere wall to catch the boundary layer effect the inflation type is first layer thickness with 20 layer and 0.1mm as first layer thickness

Mesh Quality of average 0.79395and standard deviation of 0.20589 shows that the elements are good shaped in almost all the elements 8'701'276 elements is sufficient elements number for this case study

the physical model settings are 

transient simulation with gravitational acceleration of 9.81 in the -ve Z direction

the turbulence model was set to SST K-Omega with Water as the single phase fluid

and inlet water speed of 1m/s

Different Turbulence Models were tested such as LES, DES, Reynolds stress, K-Omega and K-Epsilon but K-Omega was selected for the purpose of reducing computational resources specifically that the Domain Contains around 8.7 Million element

in solution all the residuals convergence criteria was 0.001"1e-3" that in all time step convergence occurred successfully for X Y Z velocities around 1e-7 for omega around 5e-5 for K around 5e-4 and continuity 1e-3

Wall Y+

maximum value of Y+ of 4.172 is extremely efficient and satisfactory

pressure Distribution 

pressure with centerline plane and on wall pressure

Streamlines

Turbulence

Normal Speed

Slow Motion

change of sphere diameter and velocity inlet was good to test the ANSYS optimization capabilities one of the design points faced an error and the last one was teriminated b4 reaching convergence for computational resources saving