Our customer is a diversified industrial group with interest in renewable energy technologies. The customer has identified many sites for generation of hydroelectric energy where the available head is much lesser than that required conventional turbines. Design of new turbine is being done to specifically cater to the low head areas that would generate several kilowatts of power. Basic design of the turbine has been done using first principles and the same has to be tested using CFD. To increase the efficiency, draft tube is also designed and was part of the simulation.
Turbine geometry along with rotor, stator, flow guides and entire ducting was cleaned and surface mesh was generated. Hybrid mesh with prism layer was generated with 2.9 million cells. More than half the cells had orthogonality above 0.95 and 98percentage having it greater than 0.66 with 1 as ideal value. Incompressible pressure based solver was used. k-ε turbulence model with standard wall function was used for modeling the viscosity. Moving frame of reference technique was used to model the rotor. The mesh was divided in three compartment with the stator and the inlet duct being one part, rotor portion being the second and guide vanes with draft tube (not shown in figure) being the third. Care was taken to increase the density of points at leading edges of rotor and stator, junction of main shaft and rotor/stator, near the guide vanes etc. Prism layer thickness was as per Y+ requirement of turbulence model.
Customer was given the curves of performance for Efficiency, Torque and Power vs. Mass flow rate. Efficiencies of individual sub-systems like draft tube were also reported. Physical explanation was given to the results that were found to be near to the experiments done. Separating streamline was also located and reported. The results helped in redesign of the turbine at places indicated and led to more experiments.